Paralleling alternators - wiring diagram

[Bro]

I have an engine powering two modern alternators of different make, different rated outputs and running at different speeds. If it is at all possible to safely parallel these alternators and there is a wiring diagram previously posted on this forum will someone please point me to it.

[Biggles]

There is a pinned in Equipment I think.

 

I can't see any reason why these cant be paralleled. I did mine. Well worth it..

[Keeping Up]

Does this help?

[Sir Nibble]

My link

[Bro]

My link

 

 

 

Thanks for the wiring diagram Sir Nibble. I'm stoneage man not battery powered so don't really understand all that electrickery stuff. However, if I give the diagram to a 'leccy I'm sure he'll cope. Just two questions (1) do the diodes have a particular spec'n/ rating and (2)should there be battery isolation switches somewhere?

 

Incidentally, though I can't pretend to have understood the technical content of the thread I did enjoy the confectionery banter in the correspondence. Good to see that technically competent folk are not necessarily po-faced.

 

Does this help?

 

 

Excellent write-up by Gibbo but I was looking for a wiring diagram. Sir Nibble provided the link I needed.

 

For completeness, I think it would it be useful to the less informed if Sir Nibbles diagram were properly linked with Gibbo's text. If others think that a worthwhile suggestion then is there anyone out there able to do that?

[Sir Nibble]

The diode block is a standard split charge diode with "sense" terminal. It is also important to disconnect the field diodes within the engine alternator which may or may not be dead easy depending on the alternator fitted. A competant spark should be able to sort that.

Edited to add: isolators, yes the battery connections should be nade to the "dead" side of the isolators.

Edited November 12, 2012 by Sir Nibble

[Bro]

The diode block is a standard split charge diode with "sense" terminal. It is also important to disconnect the field diodes within the engine alternator which may or may not be dead easy depending on the alternator fitted. A competant spark should be able to sort that.

Edited to add: isolators, yes the battery connections should be nade to the "dead" side of the isolators.

 

 

Thank you "Sir".

 

So the field diodes within the engine alternator only must be disconnected and not those within the domestic alternator? Forgive my pressing the point but as you can see I know so little and need to be sure when I pass on the info to a "spark".

 

Anything else I should be aware of?

[Sir Nibble]

Thank you "Sir".

 

So the field diodes within the engine alternator only must be disconnected and not those within the domestic alternator? Forgive my pressing the point but as you can see I know so little and need to be sure when I pass on the info to a "spark".

 

Anything else I should be aware of?

Yes you've got it but much depends upon the type of alternator fitted. With some types it will be required only to connect the diodes. If you can give us an idea of what's on there, or a picture, then I can give you a more definative steer.

[Chris Pink]

For completeness, I think it would it be useful to the less informed if Sir Nibbles diagram were properly linked with Gibbo's text. If others think that a worthwhile suggestion then is there anyone out there able to do that?

 

This one keeps coming up and it takes a long time to get to the final answer because it depends on so many variables.

 

I'll ask one of the mods to pin this so that we don't keep answering the same question.

 

Will paralleling alternators reduce charge times?

 

It depends upon:-

 

1. The size of the alternators in relation to the battery bank.

2. How far the batteries usually get discharged.

3. How fast the alternators are spun.

4. What other loads are being powered during charging.

 

Answers.

 

1. and 2. If the alternators are very small (say less than about 15% of the battery bank size for each alternator) then paralleling them will almost certainly reduce charge times. There is a rule of thumb called amp.hour law charging (which is actually a play on what really goes on but it suffices for this purpose). This law states a battery will safely accept a charge current in amps equal to the number of amp.hours that need replacing. So a 400Ahr bank, at 50% SoC needs 200Ahrs replacing therefore it will accept a charge current of 200amps. After a short while that bank will have increased to 51% SoC, so now it will accept 196 amps. And so on.

 

It can thus be seen that the idea of an alternator sized to 10% or 15% is complete crap. An alternator much bigger than this can be used and will result in massively reduced recharge times. If the batteries only ever get discharged to 90% SoC then at that state, the same 400Ahr bank will only safely accept 10% of 400 = 40 amps. So there is no point whatsoever in fitting an alternator bigger than this or in paralleling two 70 ampers. It would achieve nothing. But how many people only discharge to 90%?

 

On a 400Ahr bank, with twin 70 amp alternators, parelleling them will almost certainly reduce recharge times. Anyone who says otherwise simply hasn't understood what is going on.

 

3. A huge problem on the inland waterways is alternators not being spun fast enough. Most marinisers (read engine painters) don't pulley the alternators up high enough. They have many excuses for not doing so, but whatever their excuse, it doesn't change the fact that they don't pulley them up properly. They might feel justified in leaving the alterntor spinning too slowly, they might be just saying things to justify their laziness in not being bothered to change the pulleys, but it doesn't change the reality. This isn't just my opinion, this is fact. Adverc reach exactly the same conclusion on their website. This means that the alternator does not produce anywhere near its full capability at tickover. If the engine is being run at tickover just to charge batteries then paralleling the alternators will almost certainly result in a massive increase in charge rate. On many off the shelf "canal boat" engines you typically double the charge curent at tickover by paralleling them.

 

4. A 70 amp alternator (even assuming it's pulley'd up properly) isn't going to put much charge into a battery if there is an inverter running at the same time pulling 71 amps from the batteries. In fact there will be a continual 1 amp discharge. In this case, paralleling up the other alternator will turn this into a charge.

 

So you can see from the above that paralleling them can make a huge difference in many instances.

 

Alternators don't "fight each other" if paralleled. During the bulk stage (ie when the extra current is needed) they both work at full hoot. When acceptance is reached (ie the regulation voltage of the alternators), one of them might shut down completely. This is no issue, it has only shut down because its charge current is no longer needed to maintain the battery voltage at acceptance. If its current was needed, it wouldn't have shut down in the first place because the voltage wouldn't have reached acceptance. If loads are put on that exceed the capability of the remaining alternator, then the other one will instantly fire back up again. Whether one alternator shuts down or not depends upon its regulator and in particular whether it is battery sensing (most external regs) or machine sensing (most internal regs). Machine sensing ones rarely shut down, battery sensing ones often do shut down.

 

One issue that can rear its head is that the alternator shutting down can cause its charge warning light to come on and/or its tacho to stop working. This is a difficult (though not impossible) one to crack. With SmartGauge and SmartBank Advanced there is a feature built in to stop this happening.

 

I see the external reg issue has come up again. With modern alternators they do nowt. Absolutely nothing. All they ever did was increase the charge voltage. That is it. The rest is marketing bullshit. Modern alternators already charge at the same voltage so adding one does nothing. Some mention the virtue of converting to battery sensing as this compensates for the losses in under sized battery cables and dodgy battery isolators. I maintain it is better to get rid of the losses that battery sensing tries to bodge its way round. This is achieved simply by replacing the battery cables with correctly sized cables and putting in proper battery isolators.

 

When I used to actually wire boats up, as opposed to designing the equipment, I paralleled up literally hundreds of alternators, probably thousands. Every single one I did saw a reduced charge time of at least 20%, many as much as 30% and several by 50% or 60%

 

Finally, don't think of it as paralleling the alternators. Think of it as paralleling the batteries. A subtle difference, but realise that, as a result of this subtle difference, if an alternator packs up, you will still get charge to both battery banks without lifting a finger. You can also emergency start the engine from the domestic bank via the split charge relay.

 

from original post

 

 

 

OK, the domestic alternator connects to the domestic batteries.

The output from the engine alternator connects to 3 diodes, one is backfed to the field +ve on the regulator and thence to + brush. The alternator senses on this and therefore the diode voltage drop is compensated for. The other 2 diodes are connected each to one of the batteries.

Turn on, warning lamp current flows to the field and alternators excite and cut in. The domestic alternator begins to charge the domestic battery. Voltage is say 13.5 and alternator is delivering full whack to try and drive it higher.

Engine alternator is regulated at 14.2 but is also unable to drive the domestic voltage (Via the diode) that high and so is delivering full whack to try to do so. Engine battery is also recieving a small charge.

Domestic battery voltage slowly rises until it reaches 14.2 and engine alternator begins to regulate. Domestic alternator is set at say 14.6 for the sake of argument regulated by a sterling pdar, and so until voltage reaches this level it continues to run flat out. Output from engine alternator slowly falls until voltage on domestics reaches 14.3 at which point all the engine alternator output is flowing to the engine battery alone and the domestic alternator is working flat out until 14.6 is reached and the acceptance phase begins.

 

 

 

 

from original post

Edited November 12, 2012 by Chris Pink

[steelaway]

I have an engine powering two modern alternators of different make, different rated outputs and running at different speeds. If it is at all possible to safely parallel these alternators and there is a wiring diagram previously posted on this forum will someone please point me to it.

 

 

 

You can do this easily with one of THESE

 

Alex

[Bro]

You can do this easily with one of THESE

 

Alex

 

 

Thanks Alex

 

I'd pretty much made my mind up to adopt Sir Nibb's solution. Those who know about these things on this forum have given it the big thumbs-up, but I'm ever open minded.

 

The Stirling box of tricks seems phyically large and not inexpensive (I wonder how cost compares to what a 'leccy might charge to incorporate Sir Nibb's mod's?). Also, did I not read somewhere on this forum that the Sterling 'Alternator to Battery Charger' is not univerally admired?

 

In favour of the Sterling kit though would be no alternator mods required (disconnecting diodes) and subsequently alternator warranty issues would arise I suppose.

 

from original post

 

 

 

 

 

 

from original post

Thanks Chris. What I really meant, and didn't make clear, was that the circuit drawing might be appended to Gibbo's 'Pinned' contribution.

[Keeping Up]

Note that the two posts are separate because they refer to different ways of doing things.

 

Gibbo's post refers to the simple and cheap solution of just paralleling the alternators with the aid of a relay, whereas Snibble's circuit is more sophisticated but may require additional modifications to be made.

 

That is not to say that most of Gibbo's text isn't still true if you use Snibble's circuit.

[Bro]

Yes you've got it but much depends upon the type of alternator fitted. With some types it will be required only to connect the diodes. If you can give us an idea of what's on there, or a picture, then I can give you a more definative steer.

 

Please forgive the delay in responding but I've only just been to the boat and now have more info.

 

The domestic batteries alternator is marked:- Iskra, AAK3346 14V/70A, 11.201.956, 08-297.

The engine start battery alternater is marked:- 90AMP/12V alternator, HMI Pt No: 900383-ALS.

 

In appearance the two alternators are not alike. The engine start alternator however does look similar to that of the drawing in the Isuzu Hanbook (which has a front flange with three holes atop for an attachment bracket). The Isuzu drawing gives that to be a 80A Prestolite (but note mine is 90A).

 

HMI were, I believe, Isuzu Agents but are no more. I suspect this 35HP engine, though itself new/unused, may have been fitted with alternators conveniently available to a boatyard when they installed it as a replacement engine in the boat and perhaps they are not to HMI original spec'n. (the handbook specifies 80A Presolite alternators for both enagine and domestic).

 

I don't know if this info helps at all but it's the best I can offer and if you can give more guidance as to what must be connected/ disconnected in order to parallel them I shall be most grateful.

[Eeyore]

Please forgive the delay in responding but I've only just been to the boat and now have more info.

 

The domestic batteries alternator is marked:- Iskra, AAK3346 14V/70A, 11.201.956, 08-297.

The engine start battery alternater is marked:- 90AMP/12V alternator, HMI Pt No: 900383-ALS.

 

In appearance the two alternators are not alike. The engine start alternator however does look similar to that of the drawing in the Isuzu Hanbook (which has a front flange with three holes atop for an attachment bracket). The Isuzu drawing gives that to be a 80A Prestolite (but note mine is 90A).

 

HMI were, I believe, Isuzu Agents but are no more. I suspect this 35HP engine, though itself new/unused, may have been fitted with alternators conveniently available to a boatyard when they installed it as a replacement engine in the boat and perhaps they are not to HMI original spec'n. (the handbook specifies 80A Presolite alternators for both enagine and domestic).

 

I don't know if this info helps at all but it's the best I can offer and if you can give more guidance as to what must be connected/ disconnected in order to parallel them I shall be most grateful.

Hello Bro

The start battery alternator is standard for latter builds, they did at various times have similar looking 70, 80 or 90 amp units manufactured by Prestolite (and based on an earlier lucas A127). The domestic alternator was either the same as the start alternator or a 110 amp Prestolite unit, possibly an AVI128 or AS128I type driven by a polyvee belt. So you appear to be right about about the source of the domestic alternator. Just fitting the relatively inexpensive genuine domestic alternator (90amp with vee belt, 110 with polyvee belt) would probably solve your charging issues.

Steve

Edited November 24, 2012 by Eeyore

[Sir Nibble]

Please forgive the delay in responding but I've only just been to the boat and now have more info.

 

The domestic batteries alternator is marked:- Iskra, AAK3346 14V/70A, 11.201.956, 08-297.

The engine start battery alternater is marked:- 90AMP/12V alternator, HMI Pt No: 900383-ALS.

 

In appearance the two alternators are not alike. The engine start alternator however does look similar to that of the drawing in the Isuzu Hanbook (which has a front flange with three holes atop for an attachment bracket). The Isuzu drawing gives that to be a 80A Prestolite (but note mine is 90A).

 

HMI were, I believe, Isuzu Agents but are no more. I suspect this 35HP engine, though itself new/unused, may have been fitted with alternators conveniently available to a boatyard when they installed it as a replacement engine in the boat and perhaps they are not to HMI original spec'n. (the handbook specifies 80A Presolite alternators for both enagine and domestic).

 

I don't know if this info helps at all but it's the best I can offer and if you can give more guidance as to what must be connected/ disconnected in order to parallel them I shall be most grateful.

Easy. Remove the regulator by undoing the 3 screws and easing it clear of the alternator. Pull off the wire connected to it and tuck it away. Connect a new wire to it and run this one to the sense terminal on the diode block, refit the regulator. Disconnect the warning light wire from the back of the alternator and run that to the same sense terminal, job done.

[Bro]

Hello Bro

The start battery alternator is standard for latter builds, they did at various times have similar looking 70, 80 or 90 amp units manufactured by Prestolite (and based on an earlier lucas A127). The domestic alternator was either the same as the start alternator or a 110 amp Prestolite unit, possibly an AVI128 or AS128I type driven by a polyvee belt. So you appear to be right about about the source of the domestic alternator. Just fitting the relatively inexpensive genuine domestic alternator (90amp with vee belt, 110 with polyvee belt) would probably solve your charging issues.

Steve

 

Thanks EEyore for the information on Isuzu alternators, most useful.

 

What do you think, would there be any gain in swapping the alternators ie. using the 70A for the engine start battery and the 90A for the domestic bank? Present arrangment having the smaller (70A) output alternator going to the domestic bank seems illogical to me. But then, perhaps the 70A alternator being 14V rated gives better performance overall?

 

Wish I knew how this electrickery works!

[Bro]

Easy. Remove the regulator by undoing the 3 screws and easing it clear of the alternator. Pull off the wire connected to it and tuck it away. Connect a new wire to it and run this one to the sense terminal on the diode block, refit the regulator. Disconnect the warning light wire from the back of the alternator and run that to the same sense terminal, job done.

 

Thank you "Sir". You do indeed make it sound easy but if push comes to shove I shall pass your wisdom to a man who knows and stand well back.

 

Eeyore has provided good background on Isuzu alternators and it seems they tried various combinations. On the face of it my set-up sounds not any of their options and possibly least suitable. I've asked him if there might be benefit in swapping the alternators so the bigger output one would then serve the domestic bank.

 

If swapping would give significant improvement then likely that would be a first step. Nonetheless, paralleling may well be the final solution and particularly so if I add further battery to the domestic bank (which I am considering).

[Eeyore]

Thanks EEyore for the information on Isuzu alternators, most useful.

 

What do you think, would there be any gain in swapping the alternators ie. using the 70A for the engine start battery and the 90A for the domestic bank? Present arrangment having the smaller (70A) output alternator going to the domestic bank seems illogical to me. But then, perhaps the 70A alternator being 14V rated gives better performance overall?

 

Wish I knew how this electrickery works!

Good morning Bro

Just to say that I am an avid follower of the parallelling threads on here; its some of the best "alternator porn" around. Its sound advice regardless of anything you choose do do about your non standard instalation.

Both alternators are designed to charge "12 volt" systems. One has the nominal system voltage of 12 volts on the label; the other has something closer to it output voltage on the label. Both will typicaly have an output in the 14 to 14.6 volt range; its a standards verses marketing thing!

Putting the domestics on the 90 amp alt is mechanicaly the same as reverting to a single alternator system; you will be placing all the load on the belt which also drives the water pump. The belt will wear out more frequently (reducing reliability) and you will need to remove the other belt for access each time.

I have to confess to being a fan of where "simple" meets "standard"; which in this case would be having the domestic alternator that was intended for the engine.

Steve

Edited November 25, 2012 by Eeyore

[Bro]

Good morning Bro

Just to say that I am an avid follower of the parallelling threads on here; its some of the best "alternator porn" around. Its sound advice regardless of anything you choose do do about your non standard instalation.

Both alternators are designed to charge "12 volt" systems. One has the nominal system voltage of 12 volts on the label; the other has something closer to it output voltage on the label. Both will typicaly have an output in the 14 to 14.6 volt range; its a standards verses marketing thing!

Putting the domestics on the 90 amp alt is mechanicaly the same as reverting to a single alternator system; you will be placing all the load on the belt which also drives the water pump. The belt will wear out more frequently (reducing reliability) and you will need to remove the other belt for access each time.

I have to confess to being a fan of where "simple" meets "standard"; which in this case would be having the domestic alternator that was intended for the engine.

Steve

 

Hi Steve

 

If I read you correctly you are not in favour of swapping so that the 90A alternator then charges the domestic batteries and the 70A charges the engine battery. But did you not say some Isuzu engines were actually fitted with a 90A domestic alternator? If so, why would that not be a good idea in my case?

 

I take your point about belt wear and I'm prepared to accept the extra maintenance aspect if it will provide quicker charging of the domestic batteries.

 

I really do not understand why a 90A alternator should be thought necessary for the engine start battery. My previous boat had Beta 38HP engine and that was fitted with 45A alternator for the engine battery (if I remember correctly) and that coped no trouble at all.

[dmr]

If you plan to parallel the alternators then it really does not matter that much which battery is connected to which alternator as they will be working together for the bulk part of the charging when high output is required.

 

Its a good idea to un-parallel the alternators once the charge current falls to a lowish value (absorption phase) as the domestic and starter batteries may have different voltage preferences. If you have a Smartguage I think it has a voltage sensitive switch that a clever electrical person could use for this purpose.

In my humble opinion alternator paralleling is a very good thing indeed.

I have devised my own circuit for this but am not brave enough to put it on this forum!!!!

 

...........Dave

[by'eck]

I don't think swapping the 70 amp alternator for the 90 amp one will offer that much in terms of reduced charge times unless you happen to know the larger one produces more volts due to regulator or higher spin speed.

 

Paralleling them though such that both charge the domestic bank will make a noticeable improvement though. Approaching near full charge one of the two will effectively go into idle with no other significant loads, but will still be there when needed.

 

However daunting the advice given may seem, its the way to go. Get someone else more capable to do the work if necessary.

[Eeyore]

Hi Steve

 

If I read you correctly you are not in favour of swapping so that the 90A alternator then charges the domestic batteries and the 70A charges the engine battery. But did you not say some Isuzu engines were actually fitted with a 90A domestic alternator? If so, why would that not be a good idea in my case?

 

I take your point about belt wear and I'm prepared to accept the extra maintenance aspect if it will provide quicker charging of the domestic batteries.

 

I really do not understand why a 90A alternator should be thought necessary for the engine start battery. My previous boat had Beta 38HP engine and that was fitted with 45A alternator for the engine battery (if I remember correctly) and that coped no trouble at all.

Hi Bro

Yes its just the extra mainenance and reliability I would be concerned about.

I once asked HMI why they fitted a 70/80/90 amp alt for the starter; the answer was something like "why not"!

Steve

Edited November 27, 2012 by Eeyore

[Bro]

Hi Bro

Yes its just the extra mainenance and reliability I would be concerned about.

I once asked HMI why they fitted a 70/80/90 amp alt for the starter; the answer was something like "why not"!

Steve

 

 

The general concensus, now endorsed by 'By'eke', is that paralleling is the best all round approach so that's what I shall do (using 'Sir Dibble's' scheme).

 

Likely HMI's answer was simply a reflection on their parts policy and whatever they had most of in stock at any particular time is what was fitted and nothing to do with most efficent in an engineering sense. To use same alternator for both domestic and engine would cut down the number of parts held in stock and may outway the diffence in cost between holding both smaller and larger alternators (effectively doubling the stock holding).

 

Unless anyone else has something to add I think I've drained the collective brains and made my mind up on this issue. All that remains is to thank all who contributed for their interest and for giving up so freely of their opinions and valuable expertise. Hopefully, on some other topic I may be able to contribute and repay my debt to this excellent site and it's members.

[Eeyore]

The general concensus, now endorsed by 'By'eke', is that paralleling is the best all round approach so that's what I shall do (using 'Sir Dibble's' scheme).

 

Likely HMI's answer was simply a reflection on their parts policy and whatever they had most of in stock at any particular time is what was fitted and nothing to do with most efficent in an engineering sense. To use same alternator for both domestic and engine would cut down the number of parts held in stock and may outway the diffence in cost between holding both smaller and larger alternators (effectively doubling the stock holding).

 

Unless anyone else has something to add I think I've drained the collective brains and made my mind up on this issue. All that remains is to thank all who contributed for their interest and for giving up so freely of their opinions and valuable expertise. Hopefully, on some other topic I may be able to contribute and repay my debt to this excellent site and it's members.

Hi Bro

It would be realy good if you could come back to this with a "how I did it" post; and maybe a photo or two.

Feed back is realy useful.

Good luck with the work.

Steve

Edited November 28, 2012 by Eeyore

[Bro]

Hi Bro

It would be realy good if you could come back to this with a "how I did it" post; and maybe a photo or two.

Feed back is realy useful.

Good kuck with the work.

Steve

 

 

I'm doing a complete refit to the boat (previously a semi-trad. dayboat will become full trad. and totally revised inside) so it will take some time before I'm able to do all the work and run it sufficient to evaluate the various alterations. But yes, I'll follow up with feedback when able.

 

Thanks again.