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chris w

Alternator Paralleler Circuit

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I have started a new thread on this topic so the info doesn't get buried in the other long thread. I mentioned, in that other thread, that I had paralleled my alternators and it worked great. I have now gone from experiment to finished state and have attached a circuit diagram for paralleling the alternators which includes some safety aspects.

 

I have 2 x 80A alternators; one serving the start battery and one serving the domestic batteries. The start battery alternator is wasted as after about 15 minutes it's supplying virtually no current to the start battery (as starting the engine uses about 1AH only). whereas the domestic alternator is working flat out. On my 2: 1 pulley ratio, the "80A" alternator will actually only supply a maximum of around 52A.

 

The advantages of paralleling the alternators is that the start alternator's capability can be directed into the domestic batteries as well, doubling the charge current.

 

The circuit is actually very simple although it might not look so at first glance.

 

alternatorparalleler-1.jpg

 

 

 

1. The power for the circuit is obtained through the ignition switch so that there is no possibility of switching off the engine and leaving the start and domestic batteries linked up together. (You don't ever want to run the start battery down AND have no power left in the domestics either!)

 

2. The main switch I used for the cicuit is a so-called "missile switch" which has a protective cover. You buy the cover and the switch separately (Maplin). The actual switch I chose is a 3 position switch ("OFF - ON - Momentary") ie: there are two switches in the one switch housing but operated by a single toggle. The first click switches on the switch marked "ON/OFF" in the diagram. I can then push the switch toggle to a third position which is sprung-loaded and momentarily closes the "Momentary switch" in the diagram. The switch then returns to the middle ON position. If you close the red cover of the switch the switch returns to its OFF position.

 

missileswitch.jpg

 

3. When I toggle the momentary switch it allows current to flow through a bog-standard car relay (just one I had lying around) whose contacts close and are wired in parallel with the sprung-loaded toggle switch. So the closed contacts bypass current around the sprung-loaded switch (which is now open) and this current holds the relay ON.

 

4. Current can now reach the Allbright 12v (continuous) relay (also known as a "contactor"). This device uses about 1A to operate but its contacts can switch 150A continuously. clicky It's priced at £36 inc VAT and is a hefty beast.

 

5. The Albright relay closes and joins the B+ outputs of both alternators together. I used the battery isolator switch terminals as a convenient connection point for this.

 

6. If the ignition is turned off the current to the relays is interrupted and the alternators separate. When the ignition is turned back ON, the alternators stay separated unless and until you manually toggle the sprung-loaded switch.

 

7. If the missile switch is closed the alternators separate. They remain separated unless and until you manually move the toggle switch to its ON position AND then toggle the sprung-loaded switch.

 

8. I have included a red LED (mounted on the instrument binnacle) which illuminates when the alternators are joined together.

 

9. The results are amazing. At idle, with reasonably discharged batteries I used to get about 26A charge current from the domestic alternator. When conjoined, the alternators deliver double this (over 50A) AT IDLE REVS. When I increase the revs I can get close to 100A from this setup.

 

10. I do not need to join the alternator field connections together; here is my reasoning. The start alternator is regulated to 14.2v internally. Likewise the domestic alternator but this also has a Sterling alternator regulator fitted (PDAR) which lifts the alternator's regulator voltage to 14.8v eventually. However, by the time that the domestic batteries reach 14.2v, the current requirement has dropped sufficiently that the domestic alternator can supply all the necessary current on its own (about 50A). Even when the PDAR kicks in the current requirement is still no more than 50A at the start of the 14.8v acceptance cycle, and dropping steadily down. ie: the alternator is no longer rev-limited and so can cope on its own. If you have less than about a 70/80A nominally rated alternator this may not be the case for you.

 

11. The cables used to supply the circuit carry no more than 1A (to operate the Albright relay) with the exception of the two cables on the output of this relay which actually join the alternators together. I kept the lengths of these very short (about 18" each) and used 40mm2 cable)

 

12. What about the poor start battery you ask? No issues; the start battery will draw whatever current it needs (about 1-2A) to replace the energy used in starting the engine and is unaffected by the parallel alternators. It will not be overcharged in any way. Once I note that the domestics are up to 14.2v on the instrument panel voltmeter, I shall switch off the missile switch anyway separating the alternators again.

 

13. The next stage of development is to incorporate an "auto/manual" switch and a simple voltage detection circuit which, in auto mode, will detect the batteries have reached 14.2v and will automatically open a third switch to interrupt the supply to the relay thus separating the alternators automatically.

 

14. My tacho is connected to my domestic alternator "W" connection and worked perfectly throughout the paralleling (and afterwards!!)

 

15. Should your start battery ever fail, this is also a nifty circuit to have in order to temporaily connect the domestic batteries to the start motor for an "emergency start".

 

16. The function of the reversed diode (D2) is to remove any spikes from the relays' switching. Relays can produce a potentially high reverse spike when the current to them is cut-off. The diode makes sure that any reverse spike is grounded.

 

I hope this is useful... I'll await the questions!!

 

Chris

Edited by chris w

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I can't see the diagrams due to my office pc being castrated as far as anything that uses more bandwidth than a comma goes, but the description sounds very workable. might I suggest that rather than building a voltage sensitive circuit you can use the engine alternator regulator to drop the relay retaining circuit and make use of the voltage sensitive circuit that already exists.

Nice one Chris.

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That was my thinking too. The voltage detection circuit will compare the regulator output of the alternator to a 14.2v refererence and separate the alternators once that voltage is reached. I'll probably make it 14.4v just to ensure that the voltage is at a sufficient level (ie: the current is low enough) that one alternator can cope on its own.

 

Chris

Edited by chris w

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How about putting the -ve from your latched relay through the reg, that way as soon as the reg begins to switch the relay will drop out and you don't need any additional components.

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Brilliant!!!

 

If I connected the relay -ve to one of the regulator field connections then the relay would indeed be supplied with voltage (ie: reg field [relay -ve] would be near enough zero volts) whilst the reg threshold is below 14.2v. But once the reg threshold is reached, the field voltage (relay -ve) will rise to 14.2v and the voltage across the relay will drop to zero and the relay will delatch.

 

The only possible issue is that the switching frequency of the regulator will be too high to give the relay time to drop out. Oh well I guess I need to go try it!!

 

Chris

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Chris, have you included the "car type" relay in this just so that you can automatically switch it off once the voltage rises - otherwise you could just use a normal switch ?

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You could certainly get rid of the car-type relay (ie: just have an ON/OFF switch) but you would lose an important aspect of safety and a battery life consideration.

 

If there were just an ON/OFF switch for the circuit and and you turned off the ignition, then the moment you turned the ignition back on (to start the engine for example) the alternators (and the batteries) would all still be paralleled and you would be using the domestics to start the engine as well which is not good for their longevity. The voltage drop on starting may also cause your inverter to drop out and your fridge to latch out too etc.

 

By using the relay in a latching circuit, the moment I switch off the ignition (or close the "missile switch"), the relay drops out and CANNOT be reactivated by simply switching on the ignition again. One must also push the momentary switch. If you follow the circuit through carefully you will see how the relay's own contacts latch the relay ON only whilst power is applied to the circuit.

 

Hope that makes sense?

 

Chris

Edited by chris w

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The only possible issue is that the switching frequency of the regulator will be too high to give the relay time to drop out. Chris

No issue, if the regulator open circuits for sufficiently long for the relay armature to move enough for contact to break it will drop out. If not, then with the second alternator driving voltage up higher, it soon will!

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No issue, if the regulator open circuits for sufficiently long for the relay armature to move enough for contact to break it will drop out. If not, then with the second alternator driving voltage up higher, it soon will!

That's the question really. Does the regulator switch at a low enough frequency for the current through the coil of the relay to decay enough for the relay to drop out (v=Ldi/dt) before the next voltage pulse comes along? I did once measure the switching frequency but can't find my notes at the moment. :lol:

 

Chris

Edited by chris w

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That's the question really. Does the regulator switch at a low enough frequency for the current through the coil of the relay to decay enough for the relay to drop out (v=Ldi/dt) before the next voltage pulse comes along? I did once measure the switching frequency but can't find my notes at the moment. :lol:

 

Chris

I really don't think it will be an issue, how long will the reg spend switched on when the other alternator under the influence of it's higher voltage reg has reached 14.5V? The only thing that may happen is the unlatching may be delayed for a decimal point or two. Stick a quench diode across the relay winding, that should help, probably a sensible safety precaution anyway.

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Why not just energise the paralleling relay from D+ terminal of higher voltage alternator and have done with all that other cr*p?

 

Gibbo

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Because I want it to be my conscious decision to engage the paralleler and not have it come on automatically as soon as the engine is running. While a simple ON/OFF switch could achieve that between the relay and the D+ circuit, I would still have to remember to turn that switch OFF again before the next engine start.

 

With the way I have things arranged now, it takes a definite decision every time to engage the circuit. Further, since one of my alternators has a PDAR attached, I do not want to inadvertently run my start battery for hours on end at 14.8v. Connection to the D+ circuit would also not allow the batteries all to be paralleled for an "emergency start" if the start battery is on the blink. If you then decide to include a D+ bypass switch to achieve the latter, you might just as well build my circuit.

 

Chris

Edited by chris w

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Because I want it to be my conscious decision to engage the paralleler and not have it come on automatically as soon as the engine is running. While a simple ON/OFF switch could achieve that between the relay and the D+ circuit, I would still have to remember to turn that switch OFF again before the next engine start.

 

With the way I have things arranged now, it takes a definite decision every time to engage the circuit. Further, since one of my alternators has a PDAR attached, I do not want to inadvertently run my start battery for hours on end at 14.8v. Connection to the D+ circuit would also not allow the batteries all to be paralleled for an "emergency start" if the start battery is on the blink. If you then decide to include a D+ bypass switch to achieve the latter, you might just as well build my circuit.

 

Chris

 

Ok. Fair comment!

 

In that case Snibble's idea will work to switch it all off when it reraches a certain voltage. When the higher voltage alternator exceeds the lower voltage one the reg on the lower voltage one will shut down completely. It doesn't go into some sort of idle mode where it keeps a little bit going unless it's a really odd type of reg (there are one or two like that).

 

PS. That relay is 200 amps continuous not 150 amps.

 

Gibbo

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PS. That relay is 200 amps continuous not 150 amps.

 

Gibbo

The spec sheet quotes it as 200A @ 60% duty cycle and 150A @ 100% duty (ie: continuous) clicky.

 

You're right of course about the [start alternator] reg shutting down completely once the [domestic battery] alternator reg voltage exceeds the former's set reg voltage. I was overlooking that and only considering a "normal" reg set up where it is switching ON & OFF at fast speed. Another great reason to have an alternator controller :lol:

 

Chris

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The spec sheet quotes it as 200A @ 60% duty cycle and 150A @ 100% duty (ie: continuous) clicky.

 

It's the wrong datasheet. That's from an old datasheet for the industrial contactors not the power distribution contactors. The manufacturer rates them in an odd way with duty ratios and the size of conductors used (because they use the conductor for cooling). The manufacturer's rating is 150amps at 100% duty cycle with no wires on it! (yeah work that one out) rising to 200 amps 100% duty cycle with big bus bars (130 sqmm!). The proper datasheet is here............ http://www.albrightinternational.com/files...M%20LEAFLET.pdf

 

You have to deal with Albright themselves to get to the bottom of the issue!

 

You're right of course about the [start alternator] reg shutting down completely once the [domestic battery] alternator reg voltage exceeds the former's set reg voltage. I was overlooking that and only considering a "normal" reg set up where it is switching ON & OFF at fast speed. Another great reason to have an alternator controller :lol:

 

Naaa. It happens with any two alternators. One of them always shuts down.

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Stick a quench diode across the relay winding, that should help, probably a sensible safety precaution anyway.

That's a sensible suggestion. I've updated the circuit diagram in the first post. It will quench both relays as well since they have a common connection.

 

Actually the rotors in the alternators will have quench diodes across them anyway (well my A127 regs do) so these will quench the relays. But the circuit diagram shows belt and braces just in case someone's reg doesn't have a quench diode or they are not wiring it in automatic mode.

 

Chris

Edited by chris w

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Actually the rotors in the alternators will have quench diodes across them anyway (well my A127 regs do) so these will quench the relays. But the circuit diagram shows belt and braces just in case someone'e reg doesn't have a quench diode.

 

Think about that again. Your relays aren't, in any way, connected to the rotor. So the diode across the rotor won't make any difference.

 

Gibbo

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Think about that again. Your relays aren't, in any way, connected to the rotor. So the diode across the rotor won't make any difference.

 

Gibbo

Well they will be on mine because, in order to get automatic switch-off of the paralleler, the -ve side of the relay will now be connected to the field connection in the reg (ie: one side of the rotor) and the +ve side of the relay is connected to the +ve supply (ie: the other side of the rotor).

 

Chris

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Well they will be on mine because, in order to get automatic switch-off of the paralleler, the -ve side of the relay will now be connected to the field connection in the reg (ie: one side of the rotor) and the +ve side of the relay is connected to the +ve supply (ie: the other side of the rotor).

 

Chris

 

But that's not what your diagram shows!

 

And you'll still need that other diode anyway unless you connect your relay coil to the D+ terminal.

 

Gibbo

Edited by Gibbo

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But that's not what your diagram shows!

As I alluded to in my previous post, I don't know how someone will wire this up so the quench diode on the diagram is a belt and braces approach.

 

And you'll still need that other diode anyway unless you connect your relay coil to the D+ terminal.

 

Gibbo

But D+ and B+ are connected via the low resistance of the charge light so it won't make any difference by connecting to B+

 

Chris

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As I alluded to in my previous post, I don't know how someone will wire this up so the quench diode on the diagram is a belt and braces approach.

 

 

But D+ and B+ are connected via the low resistance of the charge light so it won't make any difference by connecting to B+

 

Chris

 

What wattage is the charge warning light?

 

Gibbo

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What wattage is the charge warning light?

 

Gibbo

I have a 47R resistor across mine anyway. The charge light is a 3W version so a similar resistance.

 

Chris

Edited by chris w

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I have a 47R resistor across mine anyway. The charge light is a 3W version so a similar resistance.

 

Chris

 

Are you planning connecting the small cube relay coil to the reg or the SW180 or both?

 

Gibbo

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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

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