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Alternator Paralleler Circuit


chris w

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OK I agree... the quench diode on the diagram will be needed to quench the SW180 as only the cube relay will be connected to the field connection on the reg. I could connect both to the field wire but I can't be bothered to re-route the SW180's coil -ve as I'm too lazy.

 

Chris

 

:lol:

 

And if you connected them both to the reg you'd still have to put another diode across the relay coils :lol:

 

Gibbo

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Update: I have now tried the layout with the negative of the relay connected to the field of the lower voltage regulator. The unit switches ON OK and when the domestic regulator voltage exceeds the start alternator voltage the circuit switches OFF....................... in a fashion...............

 

BUT............what happens next is as I suspected and articulated above. At the instant the circuit switches OFF, there is not enough actual time for the relay to physically open before the start regulator field (which is now separated from the domestic regulator) commences its normal high frequency switching to regulate its voltage.

 

The result is that the relay and also the contactor start chattering at high speed (and the LED of course). Even if the circuit is switched off manually, before reaching the set reg voltage (14.2v), the same thing happens. So I have, for the moment, reconnected the negative of the relay back to ground and the circuit works superbly, albeit with no auto-switch off for the time being. Both the relay and the contactor have quench diodes across them.

 

With deeply discharged batteries after a night's mooring and deliberate heavy use of the batteries, I am getting over 60A at idle and around 90A at cruising revs. I have shunt ammeters in both legs and can see that the load sharing between the 2 alternators is perfectly balanced at 50% current each. I swapped out one of the 80A alternators for a spare 70A alternator I carry and the current developed remained exactly the same.

 

I shall probably end up comparing the 2 regulators with an op-amp and use the output of that to switch the relay supply.

 

Chris

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Update: I have now tried the layout with the negative of the relay connected to the field of the lower voltage regulator. The unit switches ON OK and when the domestic regulator voltage exceeds the start alternator voltage the circuit switches OFF....................... in a fashion...............

 

BUT............what happens next is as I suspected and articulated above. At the instant the circuit switches OFF, there is not enough actual time for the relay to physically open before the start regulator field (which is now separated from the domestic regulator) commences its normal high frequency switching to regulate its voltage.

 

The result is that the relay and also the contactor start chattering at high speed (and the LED of course). Even if the circuit is switched off manually, before reaching the set reg voltage (14.2v), the same thing happens. So I have, for the moment, reconnected the negative of the relay back to ground and the circuit works superbly, albeit with no auto-switch off for the time being. Both the relay and the contactor have quench diodes across them.

 

With deeply discharged batteries after a night's mooring and deliberate heavy use of the batteries, I am getting over 60A at idle and around 90A at cruising revs. I have shunt ammeters in both legs and can see that the load sharing between the 2 alternators is perfectly balanced at 50% current each. I swapped out one of the 80A alternators for a spare 70A alternator I carry and the current developed remained exactly the same.

 

I shall probably end up comparing the 2 regulators with an op-amp and use the output of that to switch the relay supply.

 

Chris

 

Right.... the quench diodes will slow down the opening time of the relays by a substantial length of time. Keep the one on the paralleling relay as it is. In fact, if you can change it to a schottky it will delay the opening of that relay even longer. That gives you a bit more time to deal with the other relay. Now add a low value resistor series with the diode on the small switching relay. That will reduce the amount of time the relay remains closed for after the power is cut off. You need to make sure the resistor isn't such a high value that you end up with high voltage spikes everywhere. The higher the value, the faster the relay will open. You may just be able to balance the two.

 

If you still can't find a balance there is another trick you can do with diodes to still quench the voltage spike but not increase the relay opening time.

 

To give you an idea of the difference, an SW180 with no quench diode opens about 15mS after the power is cut. With a quench diode this increases to about 60mS.

 

Gibbo

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I'm in the camp of "if I could find my cashcard I would've ordered the relay by now!" but have suddenly become concerned... What's the quench diode there for?

 

edit... I don't need my cashcard, they've got Paypal... How sensible!

Edited by Smelly
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When the current through a relay coil is switched off, a high reverse voltage spike is generated (as with all coils when the current is switched off). The magnitude of this voltage is proportional to how fast the current is switched off.

 

By putting a reversed diode across the relay, the voltage across the relay is clamped to ground (well, approx 0.6v to be a purist) and the high voltage spike is suppressed (or "quenched"). It's standard practice with any relay to slap a reversed diode across it.

 

The paralleling circuit works beautifully..... it's only the auto shut off idea that needs a bit of tweaking. Manually switching the paralleler on and off has no issues.

 

Chris

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When the current through a relay coil is switched off, a high reverse voltage spike is generated (as with all coils when the current is switched off). The magnitude of this voltage is proportional to how fast the current is switched off.

 

By putting a reversed diode across the relay, the voltage across the relay is clamped to ground (well, approx 0.6v to be a purist) and the high voltage spike is suppressed (or "quenched"). It's standard practice with any relay to slap a reversed diode across it.

 

The paralleling circuit works beautifully..... it's only the auto shut off idea that needs a bit of tweaking. Manually switching the paralleler on and off has no issues.

 

Chris

 

thank you... More questions

 

You were getting 26A on the alt with the PDAR which went up to about 60 at idle, so why is the engine alt seemingly stimulating an increase over and above doubling the domestic alt?

 

How long did it take for the voltage to rise to the extent where you felt it wise to switch the switch? I know this will vary depending on SOC of the batteries, however as I've no visible volt meter from the steering position, (and won't have even when I've fitted the ammeter which I plan to do as part of this whole escapade; there's no space in the dash panel to fit it) then it'd be handy to know.

 

Would the engine battery have any effect on the charge cycle at all? With one decently charged battery connected to my 4 domestics might this reduce the DAR's equalizing cycle?

 

Finally, have you got the Maplins order codes for the diodes you used, or a spec that I can look up?

 

Ta

 

edit. What's an op amp and would it be easily fitted by someone such as myself who can crimp and measure but all electronics knowledge gained on the forum, i.e. not much?

Edited by Smelly
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thank you... More questions

 

You were getting 26A on the alt with the PDAR which went up to about 60 at idle, so why is the engine alt seemingly stimulating an increase over and above doubling the domestic alt?

The PDAR (or any other alternator controller) has no effect whatsoever until the battery terminal voltage rises to more than the alternator's own regulator voltage. So, on my set up, the alternator would normally regulate the maximum voltage to 14.2v but the PDAR allows this to increase to 14.8v. So the 26A at idle is nothing to do with the PDAR. I would get that anyway. The paralleler doubles the current available during the bulk stage so the difference between 26A the other day and 30A (doubled to 60A today) was just very slightly more revs at idle.

 

The PDAR increases the current into the batteries, over that which would be available once the batteries reach the alternator regulator's voltage (normally around 14.2v). Without the PDAR, I would normally get about 27A or thereabouts into the batteries once the batteries reach 14.2v. With the PDAR's increase to 14.8v, that current doubles to around 52A (this doubling is due to the PDAR not the paralleler). At this point, the paralleler is not needed as the current into the batteries is being limited by the batteries and not by the alternator's speed. With my "80A" alternator on the domestics, it can provide the 52A on its own and so I can switch off the paralleler if I wish.

 

The paralleler overcomes the fact that the current into the batteries during the bulk stage is usually limited by the alternator's running too slowly (ie: NB engines run at slower revs than car engines and the common 2:1 pulley ratio). Basically, a single alternator which is rev limited cannot supply all the current that the batteries can take during the bulk stage. So 2 alternators in parallel are better than one. Once the acceptance stage is reached, any alternator greater than about 70A nominal can cope on its own.

 

How long did it take for the voltage to rise to the extent where you felt it wise to switch the switch? I know this will vary depending on SOC of the batteries, however as I've no visible volt meter from the steering position, (and won't have even when I've fitted the ammeter which I plan to do as part of this whole escapade; there's no space in the dash panel to fit it) then it'd be handy to know.

 

I go by the voltmeter - when it reaches 14.3v I switch off the paralleler. In fact it's not critical as the only possible reason for switching off the paralleler anyway is to preclude the starter battery's being charged all day long at 14.8v (ie: if you have a PDAR or the like). Without a voltmeter, run the paralleler for an hour and a half and that will be fine whatever the SOC and will do no harm to the start battery.

 

 

Would the engine battery have any effect on the charge cycle at all? With one decently charged battery connected to my 4 domestics might this reduce the DAR's equalizing cycle?

 

That's actually a very astute question. The faster the domestic batteries reach 14.8v, the shorter is the acceptance cycle on the PDAR. The fact that the starter battery is connected in parallel won't make any significant difference but the 2 alternators in parallel will make a difference to the speed at which the PDAR detects that the domestics are at 14.2v. ie: the bulk stage will be shorter.

 

If the batteries have been charged faster by using the paralleler then the PDAR's calculated acceptance cycle will be shorter. But remember you have stuffed a lot more charge into the batteries in the first place because of the paralleler. So the paralleler will not adversely affect the overall charge cycle in any way.

 

Finally, have you got the Maplins order codes for the diodes you used, or a spec that I can look up?

 

Ta

Diodes are 1N4007 @ 14 pence each from maplin, code QL79L clicky

 

What's an op amp and would it be easily fitted by someone such as myself who can crimp and measure but all electronics knowledge gained on the forum, i.e. not much?

It's not something you could do yourself without reasonable electronics knowledge. If I decide to go down that route, I could build you the circuit ready for fitting for a nominal fee.

 

The other option is to add a 90 minute timer, even a kitchen timer which beeps would act as a reminder to switch off the paraller. As I said the time is not critical so long as it's not hours and hours.

 

Chris

Edited by chris w
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That's actually a very astute question. The faster the domestic batteries reach 14.8v, the shorter is the acceptance cycle on the PDAR. The fact that the starter battery is connected in parallel won't make any significant difference but the 2 alternators in parallel will make a difference to the speed at which the PDAR detects that the domestics are at 14.2v. ie: the bulk stage will be shorter.

 

If the batteries have been charged faster by using the paralleler then the PDAR's calculated acceptance cycle will be shorter. But remember you have stuffed a lot more charge into the batteries in the first place because of the paralleler. So the paralleler will not adversely affect the overall charge cycle in any way.

 

I've been waiting for this :lol:

 

You are now going to experience first hand why adaptive charging does not work.

 

With a higher bulk charge current going into the batteries they will reach acceptance in a lower state of charge than with a lower bulk current. And the adpative charging algorithm will then calculate a shorter acceptance cycle. When in actual fact it should be longer.

 

Also, a comparator on the regs will not work. It is a switching signal not an analogue signal.

 

Gibbo

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I've been waiting for this :lol:

 

You are now going to experience first hand why adaptive charging does not work.

 

With a higher bulk charge current going into the batteries they will reach acceptance in a lower state of charge than with a lower bulk current. And the adpative charging algorithm will then calculate a shorter acceptance cycle. When in actual fact it should be longer.

Why will they be in a lower state of charge? More current for less time will be around the same as less current for more time surely?

 

Also, a comparator on the regs will not work. It is a switching signal not an analogue signal.

 

Gibbo

But the regs only start to switch once the reg reaches its set voltage. Before that it's just passing rotor current without switching it.

 

The basic schematic of the A127 regulator is below (I have only omitted some speed-up caps for clarity). If D+ is below the threshold voltage, Zener D2 will not conduct and so Q3 will be OFF so Q1 and Q2 will be ON and passing rotor current. Only once the junction of R4 and R5 exceeds the Zener voltage (plus the Vbe of Q3) will Q1 and Q2 switch off thereby switching off the rotor current. Then, the decrease in rotor current will decrease D+ thereby allowing Q1 and Q2 to switch on again and so on repeating ad infinitum at high speed, ensuring that D+ never goes above the set voltage (eg: 14.2v)

 

A127AlternatorSchematicbasic.jpg

 

But below the D+ threshold voltage, the regulator is not switching. Therefore, so long as the op-amp comparator is set up to detect the two D+ voltages from the 2 alternators before their respective threshold levels, the output of the op amp can be made to drive the relay in the paralleler OFF. (If necessary, the output of the op-amp can be made to latch).

 

Chris

Edited by chris w
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Why will they be in a lower state of charge? More current for less time will be around the same as less current for more time surely?

 

Haven't we been here before?

 

At any given state of charge, a bulk charge current will drop a certain voltage across the internal battery resistance. This will cause the terminal voltage to be higher (obviously). If you double the bulk charge current, then twice the voltage will be dropped across the internal resistance at the same state of charge. Therefore the acceptance voltage will be reached with the battery in a lower state of charge when the bulk current is higher.

 

Take it to extremes:-

 

Take a completely flat 100Ahr battery and charge it with a 1 amp charger. By the time the voltage reaches 14.4 volts (or whatever acceptance voltage is chosen) the battery will be practically full. It will have taken about 120 hours. So an adaptive charger will calculate an acceptance time of, oh, a few weeks? But it's already full!

 

Do the same with a 100 amp charger. The voltage will instantly rise to the acceptance voltage in a matter of seconds, but the battery is flat as a pancake. The adaptive charger will calculate an acceptance time of what? 10 minutes? An hour? That's exactly the opposite of what is required.

 

It doesn't work!

 

But the regs only start to switch once the reg reaches its set voltage. Before that it's just passing rotor current without switching it.

 

The basic schematic of the A127 regulator is below (I have only omitted some speed-up caps for clarity). If D+ is below the threshold voltage, Zener D2 will not conduct and so Q3 will be OFF so Q1 and Q2 will be ON and passing rotor current. Only once the junction of R4 and R5 exceeds the Zener voltage (plus the Vbe of Q3) will Q1 and Q2 switch off thereby switching off the rotor current. Then, the decrease in rotor current will decrease D+ thereby allowing Q1 and Q2 to switch on again and so on repeating ad infinitum at high speed.

 

A127AlternatorSchematicbasic.jpg

 

But below the D+ threshold voltage, the regulator is not switching. Therefore, so long as the op-amp comparator is set up to detect the two D+ voltages from the 2 alternators before their respective threshold levels, the output of the op amp can be made to drive the relay in the paralleler OFF. (If necessary, the output of the op-amp can be made to latch).

 

Chris

 

Agreed. All correct. But............

 

The voltage at the D+ terminal will be rising and falling in sympathy with the switching due to the voltage drop across the D+ diode trio varying with current. It will need a fair bit of hysteresis putting on in.

 

But more importantly, you said..............

 

I shall probably end up comparing the 2 regulators with an op-amp and use the output of that to switch the relay supply

 

Which I took as meaning the reg output, not the D+ terminal.

 

Gibbo

 

Edit: Do what I suggested in post #29. It will almost certainly work

Edited by Gibbo
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The PDAR (or any other alternator controller) has no effect whatsoever until the battery terminal voltage rises to more than the alternator's own regulator voltage. So, on my set up, the alternator would normally regulate the maximum voltage to 14.2v but the PDAR allows this to increase to 14.8v. So the 26A at idle is nothing to do with the PDAR. I would get that anyway. The paralleler doubles the current available during the bulk stage so the difference between 26A the other day and 30A (doubled to 60A today) was just very slightly more revs at idle.

 

The PDAR increases the current into the batteries, over that which would be available once the batteries reach the alternator regulator's voltage (normally around 14.2v). Without the PDAR, I would normally get about 27A or thereabouts into the batteries once the batteries reach 14.2v. With the PDAR's increase to 14.8v, that current doubles to around 52A (this doubling is due to the PDAR not the paralleler). At this point, the paralleler is not needed as the current into the batteries is being limited by the batteries and not by the alternator's speed. With my "80A" alternator on the domestics, it can provide the 52A on its own and so I can switch off the paralleler if I wish.

 

The paralleler overcomes the fact that the current into the batteries during the bulk stage is usually limited by the alternator's running too slowly (ie: NB engines run at slower revs than car engines and the common 2:1 pulley ratio). Basically, a single alternator which is rev limited cannot supply all the current that the batteries can take during the bulk stage. So 2 alternators in parallel are better than one. Once the acceptance stage is reached, any alternator greater than about 70A nominal can cope on its own.

Having considered Gibbo's comments below I'd ask whether having the DAR in the circuit at all is worth it, possibly a longer acceptance cycle? Admittedly it's there anyway and it's not much to switch it if needs be.

 

 

I go by the voltmeter - when it reaches 14.3v I switch off the paralleler. In fact it's not critical as the only possible reason for switching off the paralleler anyway is to preclude the starter battery's being charged all day long at 14.8v (ie: if you have a PDAR or the like). Without a voltmeter, run the paralleler for an hour and a half and that will be fine whatever the SOC and will do no harm to the start battery.

 

That's what I thought you'd say...

 

 

 

 

That's actually a very astute question. The faster the domestic batteries reach 14.8v, the shorter is the acceptance cycle on the PDAR.]However if this isn't a linear effect, which is behind my question, then this could be detrimental The fact that the starter battery is connected in parallel won't make any significant difference but the 2 alternators in parallel will make a difference to the speed at which the PDAR detects that the domestics are at 14.2v. ie: the bulk stage will be shorter.

 

Having considered Gibbo's comments below I'd wonder whether having the DAR in the circuit at all is worth it, possibly a longer acceptance cycle? Admittedly it's there anyway and it's not much to switch it if needs be. Also

 

 

Diodes are 1N4007 @ 14 pence each from maplin, code QL79L clicky

 

Thank you!

 

It's not something you could do yourself without reasonable electronics knowledge. If I decide to go down that route, I could build you the circuit ready for fitting for a nominal fee.

 

The other option is to add a 90 minute timer, even a kitchen timer which beeps would act as a reminder to switch off the paraller. As I said the time is not critical so long as it's not hours and hours.

 

Chris

That might in interest me... I've already got the relays so a bit more of a spend won't hurt, if it will be expensive then I'll probably just remember and fry the engine battery the once to remind me not to do it again :lol:

 

 

I've just realised something... I know that something is measured by the DAR, and that for a short time there are flashy LEDs. My hindbrain has always had it that the flashy LEDs equate to the voltage rise being monitored and have been thinking the flashy LED's is the timed cycle; hence the batts were up to 14.8 inside a few minutes Assumptions aside I realise that it's the bulk phase, while the batts rise to 14.8 that's being measured...

Edited by Smelly
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Which I took as meaning the reg output, not the D+ terminal.

 

Gibbo

I meant the 2 x D+ terminals as inputs to the comparator and using its (ie: the comparator's) output to switch the relay.

 

Let me have a think overnight about what you say about adaptive charging. It seems unusual that so many well-known companies employ it (eg: Victron, Mastervolt, Sterling etc etc) and yet you say it doesn't work. Would they have not realised this by now too?

 

I want to think through the logic of what you are saying first. Prima facie, I understand what you are stating but I need to be clear that there is not some unstated secondary effect which negates the process as you describe it.

 

Edited to add: I forgot to say that I temporarily removed the quench diodes and I still had the same effect of the chattering relays once they went into "switched reg" mode. With the relay negative grounded, the effect disappeared of course. So I don't think the quench diodes are contributing significantly to the switching speed of the relays - at least, they are not being speeded up sufficiently to work in the "relay connected to field" mode. It's a bl**dy pity because it's such an intuitively pleasing solution.

 

Chris

Edited by chris w
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For the less well informed as I am I've just pulled this from Wikipedia.

 

The phenomenon of hysteresis can conceptually be explained as follows: a system can be divided into subsystems or domains, much larger than an atomic volume, but still microscopic. Such domains occur in ferroelectric and ferromagnetic systems, since individual dipoles tend to group with each other, forming a small isotropic region. Each of the system's domains can be shown to have a metastable state. The metastable domains can in turn have two or more substates. Such a metastable state fluctuates widely from domain to domain, but the average represents the configuration of lowest energy. The hysteresis is simply the sum of all domains, or the sum of all metastable states.

 

Worth a shuftie at the full article, it makes sense!

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I meant the 2 x D+ terminals as inputs to the comparator and using its (ie: the comparator's) output to switch the relay.

 

Right that's probably worth persuing. I still think it's easier to play with the diodes though to change the drop out time of the relays. I think you'll be surprised at just how much difference you can make to the relay opening time by meddling with the snubbing. At 14.4 volts I can keep an SW180 closed for over 100mS with a schottky snubber. Conversely I can open one in less than 20mS with an RC snubber.

 

Let me have a think overnight about what you say about adaptive charging. It seems unusual that so many well-known companies employ it (eg: Victron, Mastervolt, Sterling etc etc) and yet you say it doesn't work. Would they have not realised this by now too?

 

I want to think through the logic of what you are saying first. Prima facie, I understand what you are stating but I need to be clear that there is not some unstated secondary effect which negates the process as you describe it.

 

Chris

 

Aye, it's good innit.

 

There are a few points that first brought this to my attention:-

 

1. Many, many, years ago when we used to repair Heart Interface equipment their quality control insisted that every repaired Freedom combi unit was put on the test bench with a data logger and run through all cycles. This left us with loads of charge graphs that I used to (sadlly) browse through when I had nothing better to do. The Freedom charger runs a standard "acceptance until the charge current drops to a certain level" or until it timed out. We noticed on the graphs that the larger chargers ran a much longer acceptance cycle. After some thought it became clear that this was because the acceptance voltage was reached with the batteries in a lower state of charge. SG tests confirmed this. This meant that as the acceptance cycle proceeded, the current was higher. Simply because the batteries were flatter. It therefore took longer for the current to drop below the "tail current".

 

2. I know personally one of the main engineers responsible for the adaptive charging algorithm for one of the biggest names in the game. He said to me "It doesn't work, the engineers hate it, but marketing love it"

 

3. Once one of the big names have a feature, all the competition have to have it too otherwise the public think they are dragging their heels and not keeping up with new developments and ideas. Whether they work or not.

 

4. The people who have switched adaptive charging off, have found their batteries get charged better. Many people with adaptive chargers (a few on this forum) have had problems with charging batteries (as in they weren't getting charged) then cured it by switching back to a normal timed acceptance cycle.

 

5. Eventually (sometime it takes a few years) the competition catch up with me :lol:

 

Where adaptive charging can work (and maybe this is what the manufacturers had in mind) is in a fixed installation where the charger has been correctly sized to the batteries in such a way that it suits the adaptive charging algorithm. In that case, a deeper discharge will result in a longer bulk cycle, which then automatically makes the charger calculate a longer acceptance cycle. And, of course, vice versa. But if the charger size is changed, or the battery bank size changed, or the charge current is variable as with an under RPM'd alternator then the whole idea falls over and actually does things the wrong way round.

 

It can be got to work properly if the charger knows what size the charger size is (which is obviously the case with a mains powered charger, but not in the case of an alternator controller) and knows the size of the battery bank. It can't work that out for itself.

 

One day the blanks required to get it to work properly will be filled in. But at present that simply isn't the case. Though I believe by the time that day comes either lead acid batteries will be a thing of the past or a new charger type will be available that finally gets rid of all the problems currently seen.

 

Gibbo

 

Edited to add: I forgot to say that I temporarily removed the quench diodes and I still had the same effect of the chattering relays once they went into "switched reg" mode. With the relay negative grounded, the effect disappeared of course. So I don't think the quench diodes are contributing significantly to the switching speed of the relays - at least, they are not being speeded up sufficiently to work in the "relay connected to field" mode. It's a bl**dy pity because it's such an intuitively pleasing solution.

 

There's your mistake, right there!

 

Remove the one from the small relay. You might have to play around a bit to stop the diode across the rotor from acting as a quencher. This will massively speed up the opening time of the smaller relay.

 

But keep the diode on the paralleling relay. This will slow that relay opening time long enough so the other reg doesn't kick back in while the smaller relay is still opening.

 

Gibbo

 

For the less well informed as I am I've just pulled this from Wikipedia.

 

The phenomenon of hysteresis can conceptually be explained as follows: a system can be divided into subsystems or domains, much larger than an atomic volume, but still microscopic. Such domains occur in ferroelectric and ferromagnetic systems, since individual dipoles tend to group with each other, forming a small isotropic region. Each of the system's domains can be shown to have a metastable state. The metastable domains can in turn have two or more substates. Such a metastable state fluctuates widely from domain to domain, but the average represents the configuration of lowest energy. The hysteresis is simply the sum of all domains, or the sum of all metastable states.

 

Worth a shuftie at the full article, it makes sense!

 

That is, without any shadow of a doubt, the most 'orrible, unclear, b*ll*x, description of hysteresis I have ever read in my entire life.

 

Imagine a thermostat on a heating system that turned the heating on at 21 degress, and turned it off at 21 degrees. It will forever rattle back and forth with the heating going on and off at a ridiculous rate. Add some hysteresis, it turns it on at 20 degrees and turns it off at 22 degrees. Much better.

 

Gibbo

Edited by Gibbo
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That is, without any shadow of a doubt, the most 'orrible, unclear, b*ll*x, description of hysteresis I have ever read in my entire life.

 

Imagine a thermostat on a heating system that turned the heating on at 21 degress, and turned it off at 21 degrees. It will forever rattle back and forth with the heating going on and off at a ridiculous rate. Add some hysteresis, it turns it on at 20 degrees and turns it off at 22 degrees. Much better.

 

Gibbo

 

thank you! I liked the "informal description" bit :lol:

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I've just realised something... I know that something is measured by the DAR, and that for a short time there are flashy LEDs. My hindbrain has always had it that the flashy LEDs equate to the voltage rise being monitored and have been thinking the flashy LED's is the timed cycle; hence the batts were up to 14.8 inside a few minutes Assumptions aside I realise that it's the bulk phase, while the batts rise to 14.8 that's being measured...

I missed this query earlier.

 

The "flashing" LED at the beginning of the charge cycle on the DAR is actually the "slow start" system in operation. The DAR (and the PDAR) ramps up the current over a short period of time to reduce the chance of alternator belt slip. The slow start period lasts for about 2 minutes.

 

Typically, you will need about an hour to an hour and a half to get your batteries from 50% discharged to the end of the bulk stage (14.8v).

 

Chris

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Haven't we been here before?

 

At any given state of charge, a bulk charge current will drop a certain voltage across the internal battery resistance. This will cause the terminal voltage to be higher (obviously). If you double the bulk charge current, then twice the voltage will be dropped across the internal resistance at the same state of charge. Therefore the acceptance voltage will be reached with the battery in a lower state of charge when the bulk current is higher.

 

Take it to extremes:-

 

Take a completely flat 100Ahr battery and charge it with a 1 amp charger. By the time the voltage reaches 14.4 volts (or whatever acceptance voltage is chosen) the battery will be practically full. It will have taken about 120 hours. So an adaptive charger will calculate an acceptance time of, oh, a few weeks? But it's already full!

 

Do the same with a 100 amp charger. The voltage will instantly rise to the acceptance voltage in a matter of seconds, but the battery is flat as a pancake. The adaptive charger will calculate an acceptance time of what? 10 minutes? An hour? That's exactly the opposite of what is required.

 

It doesn't work!

 

 

Gibbo

 

I've been trying to get my head around this one. One point you haven't addressed is that, as the battery charges, its internal resistance falls in value. So, with a higher charge current, the internal resistance will fall at a much faster rate than with a smaller charge current because the battery is receiving a faster charge.

 

The terminal voltage that is physically available and actually measured is the inherent (open-circuit) voltage of the battery plus the product of charge current x internal resistance (as you alluded to as well). As the battery charges, its o/c voltage will rise, of course, BUT the voltage drop across the internal resistance will fall as the internal resistance itself falls in value. So the terminal voltage will be the result of the increasing o/c voltage PLUS the decreasing voltage across the internal resistance. This will slow the rise of the overall terminal voltage measurement.

 

Thus the two effects work in opposite directions and the terminal voltage will not rise as fast as might be imagined with a larger charging current owing to the mitigating effect of the falling internal resistance. Your analysis made the implied assumption that the internal resistance stayed constant whereas, in reality, the internal resistance may decrease by a factor of 3 or 4 as the battery charges (from say 30 or 40 milliohms when discharged to 10 milliohms or less when charged).

 

 

A second issue, to my mind, is one of comparative acceptance cycle times. Let's analyse my 40A Sterling charger for example. We don't know for sure whether the acceptance times it calculates are really correct or not.

 

However, what we do know is that because the charge current is 40A (in the bulk stage) each and every time it charges my batteries, then a heavily discharged battery WILL take longer to reach 14.4v or 14.8v than a less discharged battery. So the heavily discharged battery WILL get a longer calculated acceptance time than a less discharged battery which is what is required.

 

Chris

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I did a really long reply to this addressing all your points but I really fail to see the point.

 

I'll just say this:-

 

Get two identical batteries at the same state of charge, (let's go for 50%). The internal resistance will be identical.....

 

Put a 10 amp charger on one, and a 100 amp charger on the other. The one with the 10 amp charger will start to increase the terminal voltage while throwing in 10 amps. It might take 4 hours to reach acceptance. The bulk stage lasted 4 hours. It has put in 40 amp hours. The battery is at 90% state of charge. Acceptance starts. The "clever" adaptive charger calculates a 6 hour acceptance cycle.

 

The 100 amp charger will immediately raise the voltage to acceptance. The bulk stage lasted 2 seconds. The battery is at 50.00000001% state of charge. The "clever" adaptive charger calculates an acceptance cycle of a few minutes then goes into float. The battery is still half flat.

 

Using a charger somewhere in between these two extremes doesn't make things suddenly jump into a new arena. It's a straight line graph from one to the other.

 

Gibbo

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Do you two ever sleep?

 

:lol:

 

Mild insomnia has always affected me. I tend to do about 2 or 3 hours sleep a night, then about once a week will catch up with a full night. It's not through choice.

 

Gibbo

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Mild insomnia has always affected me. I tend to do about 2 or 3 hours sleep a night, then about once a week will catch up with a full night. It's not through choice.

If that's "mild" insomnia, I hope I never get the full-fat version! I'd be a zombie on that much sleep. Having small children taught me to cope on less, but I've lost even that ability now that they're teenagers and sleep 14 hours a night (well, mainly day).

 

MP.

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I have given this some thought and it seems to me that the crux of the problem is that the standard reg on the engine alternator is machine sensed and therefore will not be maintained in an open circuit condition by the higher voltage of the domestic alternator. Now horses for courses, bloke like Chris is likely to be most happy with a pocketful of semiconductors juggling milliamps but this is what I'd do.

Remove the domestic alternator regulator, cut the link between -ve brush and regulator, I would leave enough metal on the brush to curl it under the lip on the plastic brush box to secure it in place the same as the opposite side of the brush. Then connect a wire to the regulator side of the break and earth the relay through it. Now when the reg opens at 14.2 volts the voltage will not fall in response as the PDAR will continue to conduct, therefore the reg should remain open, not just long enough to drop the relay but until the engine is stopped. That's what I'd do, but then I'm used to precisely that kind of work.

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If that's "mild" insomnia, I hope I never get the full-fat version! I'd be a zombie on that much sleep. Having small children taught me to cope on less, but I've lost even that ability now that they're teenagers and sleep 14 hours a night (well, mainly day).

 

MP.

 

It's mild by my standards. I have mellowed in old age. From early teens to about 30 I would sleep maybe 3 nights per week for 1 or 2 hours. The rest of the time I was awake doing something. I remember regularly waking the babies up so I had someone to talk to :lol:

 

Gibbo

 

I have given this some thought and it seems to me that the crux of the problem is that the standard reg on the engine alternator is machine sensed and therefore will not be maintained in an open circuit condition by the higher voltage of the domestic alternator. Now horses for courses, bloke like Chris is likely to be most happy with a pocketful of semiconductors juggling milliamps but this is what I'd do.

Remove the domestic alternator regulator, cut the link between -ve brush and regulator, I would leave enough metal on the brush to curl it under the lip on the plastic brush box to secure it in place the same as the opposite side of the brush. Then connect a wire to the regulator side of the break and earth the relay through it. Now when the reg opens at 14.2 volts the voltage will not fall in response as the PDAR will continue to conduct, therefore the reg should remain open, not just long enough to drop the relay but until the engine is stopped. That's what I'd do, but then I'm used to precisely that kind of work.

 

Yeah that would work. But so will playing with the snubbers :lol:

 

Gibbo

 

Edit: Will the charge warning light come on at zero revs without the internal reg connected? I don't think the PDAR duplicates that function.

Edited by Gibbo
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Edit: Will the charge warning light come on at zero revs without the internal reg connected? I don't think the PDAR duplicates that function.

Why not? The PDAR does, does it not complete the rotor circuit to earth, and the warning light is connected to rotor +ve so the lamp should light as normal until the D+ voltage from the field diodes is established, again, as normal.

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