Alternator Paralleler Circuit

[Gibbo]

I understood that when two alternators were paralleled, the lower voltage one would at some point cut out, and it's charge warning light come on and the tacho output would stop working.

 

Maybe Smelly could parallel the two alternators manually and see what happens to the charge warning lights. If it comes on for one of the alternators, then the circuit I posted should work OK.

 

cheers,

Pete.

 

I've done this many times. The lower voltage alternator shuts down completely. The reg completely and utterly stops operating (there are one or two odd regs that don't do this but they are rare).

 

Now I've gone through the thread again and Chris said that the relay chattered so therefore the reg was still operating. That's a fair conclusion, but that's after the paralleling relay had opened so it would start operating again then. But it can't have opened until after the control relay opened. And once the control relay opened it would remove its own power feed so it simply cannot have reconnected. So it cannot have chattered.

 

So I reckon he had it wired up wrong otherwise it simply could not ever chatter.

 

The reason I am so adamant on this is that I've done exactly this same trick many, many, times and it just works. Now, with our device there's no need because it's already built in as a standard function so I haven't done it for a few years.

 

Gibbo

 

Oh... Maplins didn't have the 1N5408s in stock so I gamble a quid on 5402's instead... will they do? They're all they had in.

 

Yes you'll be fine with them.

 

Gibbo

[chris w]

I've done this many times. The lower voltage alternator shuts down completely. The reg completely and utterly stops operating (there are one or two odd regs that don't do this but they are rare).

 

Now I've gone through the thread again and Chris said that the relay chattered so therefore the reg was still operating. That's a fair conclusion, but that's after the paralleling relay had opened so it would start operating again then. But it can't have opened until after the control relay opened. And once the control relay opened it would remove its own power feed so it simply cannot have reconnected. So it cannot have chattered.

 

So I reckon he had it wired up wrong otherwise it simply could not ever chatter.

 

The reason I am so adamant on this is that I've done exactly this same trick many, many, times and it just works. Now, with our device there's no need because it's already built in as a standard function so I haven't done it for a few years.

 

Gibbo

I definitely didn't have it wired up wrongly. I simply removed the ground side of the cube relay from earth and connected it to the field brush connection of the engine alternator..........and it chattered.

 

I tried it without snubbing on either and tried it with snubbing on both - no difference. Like you, I totally understand the circuitry of the regulator. One's intuition is that it would switch off straight with no issue. But it didn't... there is some subtle interaction between the relay's switching off (which will immediately return the regulator to its normal "chattering" mode) and the speed at which the regulator can react to that relay's opening which holds the relay closed.

 

Here's another clue to the strange effect - when I first wired it up, I did inadvertently connect the cube relay ground side to the DOMESTIC alternator field wire rather than the engine alternator field. (My fault for using 2 wires of the same colour!). However, just before I spotted this error, I observed a very strange effect.......

 

With the cube relay connected to the domestic field the relay (and contactor) started chattering the moment I switched the paralleler switch ON ie: BEFORE I had even pushed the intermittent switch to switch the cube relay ON. So there was some weird interaction which could point to the reason that the relay doesn't switch off even when it is connected to the correct field.

 

Chris

Edited May 14, 2009 by chris w

[Smelly]

It's arrived, and the big cable isn't too much of a problem! My work for the weekend is cut out!

 

And it is a hefty piece of kit isn't it?

 

edit for double posting

 

edit again... I find it really quite depsarate when I work in an office where absolutely no-one apart from me is excited by the concept of REALLY BIG relays.

Edited May 14, 2009 by Smelly

[Sir Nibble]

With the cube relay connected to the domestic field the relay (and contactor) started chattering the moment I switched the paralleler switch ON ie: BEFORE I had even pushed the intermittent switch to switch the cube relay ON. So there was some weird interaction which could point to the reason that the relay doesn't switch off even when it is connected to the correct field.

 

Chris

I can't see your diagrams but, could it have been picking up the intermittant voltage appearing across the regulator?

[chris w]

I really don't know why it was doing that. But your idea is working beautifully - thank you. I was up at at the boat again today and delberately ran the vacuum cleaner on the inverter just to run the batteries down a bit so that I could use the paralleler (I know, get a life!).

 

The relay and the contactor switch off very cleanly at D+ (domestic) = 14.35v everytime. It works perfectly.

 

Chris

[smileypete]

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.

 

Think I may have spotted the problem here.

 

When the reg switches off, the field connection goes to D+, the latch relay goes to B+ at one end and D+ at the other end and the latch relay opens...

 

Surely once the latch relay opens, the contactor pulls one end of the latch relay to 0V from B+, and the latch relay is now powered in reverse from D+ at the other end and re-closes, as it has 0V and D+ at each end (formerly B+ and ~0V).

 

Once it re closes, that gives it B+ at one end and D+ at the other end once again so it opens and so on....

 

If so a solution may be to add a blocking diode so the relay can only be powered one way.

 

cheers,

Pete

[chris w]

Think I may have spotted the problem here.

 

When the reg switches off, the field connection goes to D+, the latch relay goes to B+ at one end and D+ at the other end and the latch relay opens...

 

Surely once the latch relay opens, the contactor pulls one end of the latch relay to 0V from B+, and the latch relay is now powered in reverse from D+ at the other end and re-closes, as it has 0V and D+ at each end (formerly B+ and ~0V).

 

Once it re closes, that gives it B+ at one end and D+ at the other end once again so it opens and so on....

 

If so a solution may be to add a blocking diode so the relay can only be powered one way.

 

cheers,

Pete

I think you have it. The relay will be reversed powered either through the contactor coil or through the LED to ground (more likely the contactor coil). Which would explain why the relay chatters if the trigger point is passed and just the simple ON/OFF switch is switched ON without even toucjhing the momentary switch. Well done. In which case a blocking diode would indeed solve it. I'm not going to change mine back now to try it because it's working with the other mod but I bet you're correct.

 

Chris

[Sir Nibble]

Think I may have spotted the problem here.

 

When the reg switches off, the field connection goes to D+, the latch relay goes to B+ at one end and D+ at the other end and the latch relay opens...

 

Surely once the latch relay opens, the contactor pulls one end of the latch relay to 0V from B+, and the latch relay is now powered in reverse from D+ at the other end and re-closes, as it has 0V and D+ at each end (formerly B+ and ~0V).

 

Once it re closes, that gives it B+ at one end and D+ at the other end once again so it opens and so on....

 

If so a solution may be to add a blocking diode so the relay can only be powered one way.

 

cheers,

Pete

Yes very plausible, so in effect the relay is seing a square wave ac!

[Smelly]

Well that's a relief, I even bought some spare diodes

 

Considering I'll be working down my engine bay this weekend, I would hope to feel the vibes of a number of sparky types dancing round in circles doing a sun dance... Ah one two three Um walla walla walla...

[Sir Nibble]

Well that's a relief, I even bought some spare diodes

 

Considering I'll be working down my engine bay this weekend, I would hope to feel the vibes of a number of sparky types dancing round in circles doing a sun dance... Ah one two three Um walla walla walla...

Sparky types don't do a sun dance, they close a switch and the sun obeys.

[Smelly]

Sparky types don't do a sun dance, they close a switch and the sun obeys.

 

Looking at the BBC weather forecast... a fuse has blown somewhere!

[chris w]

Since the cube relay opens a long time before the contactor (in electronic terms), based on Gibbo's results, and since we now understand the mechanism of from where the previous "chattering" arises, then I now believe the lamps in Smileypete's circuit are not needed. But the blocking diodes are still needed.

 

Chris

[Smelly]

Since the cube relay opens a long time before the contactor (in electronic terms), based on Gibbo's results, and since we now understand the mechanism of from where the previous "chattering" arises, then I now believe the lamps in Smileypete's circuit are not needed. But the blocking diodes are still needed.

 

Chris

 

I was thinking that myself, however the question comes as to whether belt and braces is needed or might I just save myself the additional faff?

 

Edit... lamp 1 will be handy as an indicator won't it?

Edited May 15, 2009 by Smelly

[smileypete]

I was thinking that myself, however the question comes as to whether belt and braces is needed or might I just save myself the additional faff?

 

Edit... lamp 1 will be handy as an indicator won't it?

Have a look at post 148, last para.

 

If there's no charge warning light coming on, when one alternator takes over and the other one cuts out, then it's very likely it'll have to be done with a field connection instead.

 

I'd also try connecting Lamp 1 and the latching relay between D+ and 0V once the engine is running, and seeing what happens when the other alternator takes over.

 

cheers,

Pete.

 

Edit:

 

If the alternator has a tacho output terminal (usually marked 'W') then the circuit I posted should work OK from that instead of D+. It could help to have a quenching diode across the latch relay as well in that case, I'll post a revised circuit diagram if need be.

Edited May 15, 2009 by smileypete

[Smelly]

Pete a revised diagram would be handy, although I can kind of see what you mean I'd rather be working from a diag from someone who knows.

 

I've finally managed to pass this past a good friend who works in the field... The one concern he's raised is having a fail safe built in in case the contactor ends up welded closed. I can see his concerns; a bad connection might push the current up and when working with welding currents; as we are, things might get... errr... sticky, if things go wrong. I'm thinking along the lines of the red key isolator switch that did the same when my inverter was fastened to it.

 

With any luck; good friend being a fellow boater, having sent this thread across not only will we get an un-involved but knowedgable view on things, but we'll also get another member (AHEM!)

[chris w]

I don't think the "welded-together" contactor is an issue in reality. All the contactor is doing is making a bank of (say) 3 batteries into a bank of (say) 4 batteries. It's no more or less dangerous than having the original bank of 3 batteries in the first place.

 

A second thing that occurred to me about the circuit is that if one has a reversed diode across the cube relay to prevent spikes, then even when D+ rises to 12v or higher, the cube relay still cant't switch ON because the voltage across it is clamped at 0.7v by the diode. However, the contactor can still be operated by current flow from D+ through this diode, through the contactor and so to ground.

 

Overnight, I tried the paralleler in anger as I was moored up and the batteries were down by about 75AH (out of a nominal 405AH total) ie: around 20% discharged. The paralleler worked perfectly when I switched on the engine to charge the batteries and switched itself OFF automatically after about an hour or so of running.

 

Smelly...... if you have to start playing around with the "field" connection in the regulator, are you au fait with what's what or do you need advice?

 

Chris

Edited May 16, 2009 by chris w

[Smelly]

I don't think the "welded-together" contactor is an issue in reality. All the contactor is doing is making a bank of (say) 3 batteries into a bank of (say) 4 batteries. It's no more or less dangerous than having the original bank of 3 batteries in the first place.

 

A second thing that occurred to me about the circuit is that if one has a reversed diode across the cube relay to prevent spikes, then even when D+ rises to 12v or higher, the cube relay still cant't switch ON because the voltage across it is clamped at 0.7v by the diode. However, the contactor can still be operated by current flow from D+ through this diode, through the contactor and so to ground.

 

Overnight, I tried the paralleler in anger as I was moored up and the batteries were down by about 75AH (out of a nominal 405AH total) ie: around 20% discharged. The paralleler worked perfectly when I switched on the engine to charge the batteries and switched itself OFF automatically after about an hour or so of running.

 

Smelly...... if you have to start playing around with the "field" connection in the regulator, are you au fait with what's what or do you need advice?

 

Chris

 

I'm not playing with the field connection Chris, not being au fait means I'm sticking with Pete's circuit as opposed to cutting into an alternator I can't afford to be without. Cheers for the concern though

 

One more coffee then it's rain coat on and hope the rain stops long enough to drill the holes for the switches... Soldering iron at the ready!

 

edit... can I crimp to the diodes or am I best soldering?

Edited May 16, 2009 by Smelly

[smileypete]

Pete a revised diagram would be handy, although I can kind of see what you mean I\'d rather be working from a diag from someone who knows.

 

Here is the diagram for using the tacho/W connection:

 

 

The extra diode (dotted line) may not be needed, but try it first.

 

The diodes are best soldered, I'd solder some stranded wire onto them then crimp onto the wire.

 

cheers,

Pete.

 

Edit

 

Here's some revised steps if you're using the tacho/W connection instead of the D+ connection:

 

When it comes to building and testing the circuit I posted, it could be best to do so in stages. I'd do this by leaving the diode between the contactor coil and latch relay contacts initially, then test each half individually in steps as follows:

 

1) First connect a 12V supply to the contactor coil fuse, and check Lamp 2 lights. Then bridge Lamp 2 and check it goes out and the contactor closes. After that un-bridge Lamp 2 and check the contactor opens and Lamp 2 lights up again.

 

2) Next connect a 12V supply to the latch relay coil fuse, and check Lamp 1 is unlit. Then press the pushbutton switch and check Lamp 1 lights up, and stays lit when the pushbutton is released.

 

3) Now connect the contactor coil fuse to the the ignition/accessory feed, and connect the contactor switching contacts between the alternators outputs. Connect a small 12v test lamp between the tacho/W output of each alternator and 0V. When the engine is running, bridge Lamp 2 and check the contactor closes. At some point one of the test lamps should go out, and it's the tacho/W connection on this alternator that is to be used for the latch relay feed.

 

4) Next connect the latch relay fuse to the tacho/W connection of the above identified alternator. When the engine is running press the pushbutton switch and check the Lamp 1 lights, and stays lit when the pushbutton is released. Stop the engine and check that Lamp 1 goes out indicating the latch relay has opened.

 

5) Finally put the diode in the middle back (the right way round of course!) and test both parts together. Edit: Before starting the engine, ensure the domestic batteries are partially flattened. When the engine is running press the pushbutton and check Lamp 1 lights and Lamp 2 goes out. Sometime later when one alternator takes over from the other, Lamp 1 should go out and Lamp 2 come back on. Cheer loudly when this happens!!!

 

6) As an extra check, when Lamp 2 comes back on the voltage across the SW180 contactor coil should be below 2.2V which is the minimum 'drop-out' voltage (the lowest voltage it can stay closed).

Edited May 17, 2009 by smileypete

[chris w]

edit... can I crimp to the diodes or am I best soldering?

Either will be fine. Crimp them if you are a novice solderer though.

 

Chris

[chris w]

Here is the diagram for using the tacho/W connection:

Note that if you are using the W connection, then the voltage applied to the relay will be much higher than 12v and will also be an AC voltage not a DC voltage.

 

Chris

[smileypete]

Note that if you are using the W connection, then the voltage applied to the relay will be much higher than 12v and will also be an AC voltage not a DC voltage.

 

Chris

 

Look at the circuit diagram in post #168 Chris, there will only be a DC voltage/current across/through the relay, due to the diode on the other side.

 

cheers,

Pete.

[chris w]

Look at the circuit diagram in post #168 Chris, there will only be a DC voltage/current across/through the relay, due to the diode on the other side.

 

cheers,

Pete.

That's true.... overlooked that. The relay still needs to be capable of handling a possibly much higher voltage than 12v though - it could be as high as 50 volts or so depending on the charge current.

 

Chris

[smileypete]

That's true.... overlooked that. The relay still needs to be capable of handling a possibly much higher voltage than 12v though - it could be as high as 50 volts or so depending on the charge current.

 

It can't rise above the level at which the main output diodes start conducting.

 

cheers,

Pete.

Edited May 16, 2009 by smileypete

[chris w]

It can't rise above the level at which the main output diodes start conducting.

 

cheers,

Pete.

Of course it can....... it can ultimately go up to about 120v !! The volts are dropped across the stator coil and then rectified by the output diodes before reaching the battery. But the stator output as seen at the W connection can be as low as about 15v up to around 120v peak depending on the alternator revs and the charging current. All alternators can be turned into 120v AC generators simply by removing the regulator and rectifier. But the W output is always unregulated and unrectified.

 

Chris

Edited May 16, 2009 by chris w

[smileypete]

Of course it can....... it can ultimately go up to about 120v !! The volts are dropped across the stator coil and then rectified by the output diodes before reaching the battery. But the stator output as seen at the W connection can be as low as about 15v up to around 120v peak depending on the alternator revs and the charging current. All alternators can be turned into 120v AC generators simply by removing the regulator and rectifier. But the W output is always unregulated and unrectified.

 

The output load (batteries under charge) will act like a shunt regulator.

 

Ask Gibbo and Snibble if you like.

 

cheers,

Pete.