Best alternator setup with lithiums?

[nicknorman]

44 minutes ago, BEngo said:

Yes,  maybe.  I also  think two identical alternators would be OK, provided the field current is acceptable to the Controller.  However, I think manufacturing tolerances might make it impracticable  because  you are not at all  likely to have identical alternators.  One would produce a little more voltage than the other,  for the same field current in each and one would have a little more field current for the same  voltage.  That will give you different output voltages and so one alternator would do more work.

How much more I have no idea.

 

N

well let us remember that an alternator controls voltage by regulating current, and that 2 alternators connected in parallel must have the same output voltage. So the outcome of manufacturing tolerances would be a slight inequality in current sharing when he alternator is not on max output, which isn’t a big deal. I would presume that the number of turns on the rotor and stator windings is well controlled, and the gap between the rotating and static bits ditto, so I would doubt there would be much current difference.

39 minutes ago, Tony Brooks said:

 

But then in many cases thee is the practical consideration of the brush holders on the "slave" alternator. I suppose the way to deal with that would be to keep its regulator in place but bypass it with a fly lead a bit like the advanced controllers use. I think the negative regulated systems would also need a positive feed to the other brush.

 

I still can't see how a 60 amp load would not pull the voltage of Tony1's alternator down so both shared the work, but he found what he found. Too many people have successfully paralleled their alternators for his problem to be a common one.

I think it always best to get rid of the existing alternator. In my case I just snipped the wires going from the reg to the brushes (combined regulator and brush module) and retired the brush connections because I needed positive regulation connections whereas the alternator was originally negative control. It was a trivial job.

 

Tony does mention a 0.4v - 0.5v difference in regulated voltage which is quite a lot, but always felt that there was something wrong with the “weak” alternator but this was never identified. Blown diode, probably.

Edited September 18, 2022 by nicknorman

[Tony Brooks]

1 hour ago, nicknorman said:

Tony does mention a 0.4v - 0.5v difference in regulated voltage which is quite a lot, but always felt that there was something wrong with the “weak” alternator but this was never identified. Blown diode, probably.

 

That pretty much accords with my feelings on this specific "problem" and it is a nice illustration as to why it is best to get a suspect to a specialist for testing rather than relying on an "on engine" diagnosis.

[Tony1]

18 minutes ago, Tony Brooks said:

 

That pretty much accords with my feelings on this specific "problem" and it is a nice illustration as to why it is best to get a suspect to a specialist for testing rather than relying on an "on engine" diagnosis.

 

Thanks for your input on this issue guys, I wish I'd asked these questions more clearly at the time, and had it looked at in a workshop rather than being under time pressure, but there you are.

 

Can I get your thoughts on something? Would a blown diode stop an alternator working completely, or would the blown diode still allow the alternator to put out 20 amps as I mentioned above? 

I did get the 'sleeping' alternator to do some charging when I increased the current draw, but it never did enough of the work to make a really useful contribution. 

 

 

Edited September 18, 2022 by Tony1

[Tony Brooks]

34 minutes ago, Tony1 said:

 

Thanks for your input on this issue guys, I wish I'd asked these questions more clearly at the time, and had it looked at in a workshop rather than being under time pressure, but there you are.

 

Can I get your thoughts on something? Would a blown diode stop an alternator working completely, or would the blown diode still allow the alternator to put out 20 amps as I mentioned above? 

I did get the 'sleeping' alternator to do some charging when I increased the current draw, but it never did enough of the work to make a really useful contribution.

 

 

A blown diode will take out about one third of the alternator currant (amps) output (note the about)., but will only drop the charging voltage by a small amount. So that 20 amps output roughly equates to a 60 amp alternator, but it is only roughly, so it could just a swell be a 50 amp one.

 

Increasing the charging current would pull the voltage produced by the "good" alternator down so the "bad" one would be able to produce more charging currant. As far as I am concerned it all suggest that one alternator was faulty with a blown diode.

 

We all live and learn and regrettably sometimes that learning costs us money.

[Jay88]

Hi all,

 

Thanks for all the responses, appreciated.

 

After doing some more research I contacted Sterling who advised to have both alternators go to the starter battery then attach their 120A DC-DC charger

at a cost of £717...bit harsh. 

 

Anyway it got me thinking and I found this Renogy 50A DC-DC charger with MPPT for £230 . So maybe I could attach one alternator to the start battery and the solar cables to the DC-DC charger (saves getting a a separate MPPT) noting that the max solar for the system is 660w, which is fine with me as I'm looking at about 600W. After reading the renogy manual, a downside I can see is that when the sun is not around and I need to start the engine to charge the lithiums, I believe I'll only ever get about 25A from the alternator as opposed to about 120A from the sterling DC-DC charger...

 

OR

 

Maybe I simply install the renogy 60A DC-DC charger between the starter and lithiums and keep the 660W solar on a separate system, atb least I'll get about 60A from when I charge the lithiums via the engine...but do I connect 1 or 2 alternators to the start battery??...hmmm

 

Thoughts?

 

Cheers!

 

[nicknorman]

1 hour ago, Jay88 said:

Hi all,

 

Thanks for all the responses, appreciated.

 

After doing some more research I contacted Sterling who advised to have both alternators go to the starter battery then attach their 120A DC-DC charger

at a cost of £717...bit harsh. 

 

Anyway it got me thinking and I found this Renogy 50A DC-DC charger with MPPT for £230 . So maybe I could attach one alternator to the start battery and the solar cables to the DC-DC charger (saves getting a a separate MPPT) noting that the max solar for the system is 660w, which is fine with me as I'm looking at about 600W. After reading the renogy manual, a downside I can see is that when the sun is not around and I need to start the engine to charge the lithiums, I believe I'll only ever get about 25A from the alternator as opposed to about 120A from the sterling DC-DC charger...

 

OR

 

Maybe I simply install the renogy 60A DC-DC charger between the starter and lithiums and keep the 660W solar on a separate system, atb least I'll get about 60A from when I charge the lithiums via the engine...but do I connect 1 or 2 alternators to the start battery??...hmmm

 

Thoughts?

 

Cheers!

 

25A charging from the alternator seems very low. There will likely be some load on anyway (eg fridge) so the actual charge current will be less than 25A, which defeats one of the main advantages of Li - ability to charge very fast.

 

The 60A dc dc looks like a good possibility on paper, though I have no experience of whether the kit is any good or not. But at least 60A is a not too bad charge rate. However there is no mention of eg protecting the batteries against being charged at below zeroC. Maybe that will be built into the BMS of your proposed Li batteries? But then again the Sterling offerings don’t seem very good- very inefficient with a lot of power converted to heat.

 

If you go that way (Renology) I’d connect both alternators to starter battery. Make sure you include the D+ wire so that the DC DC only kicks in when the engine is running. And I’d add a switch in that circuit so that you can turn off the DC DC even if the engine is running, to avoid prolonged charging at 100% during a long cruise. I’d also want reasonable monitoring of the Li SoC, using eg a BMV712. You can’t really monitor the SoC of lithium just by looking at the voltage.

Edited September 23, 2022 by nicknorman

[Tony Brooks]

I echo what Nick says about 25 amps from an alternator being rather low. I think that needs resolving so you know what you are dealing with.  Even the 50 year old 10 and 11 AC series did better than that and I think the smallest ACR was about 35 amps.

 

Low alternator output could be caused by:

 

Fairly well charge batteries

Resistance in the charging circuit (undersized cable, dirty or lose connections)

A passive split charge diode being used.

A blown diode in the alternator.

 

If you can't ascertainment the alternator's rated output post a photo showing the back of it plus something to scale it from and we can have an informed guess.

 

[nicknorman]

4 minutes ago, Tony Brooks said:

I echo what Nick says about 25 amps from an alternator being rather low. I think that needs resolving so you know what you are dealing with.  Even the 50 year old 10 and 11 AC series did better than that and I think the smallest ACR was about 35 amps.

 

Low alternator output could be caused by:

 

Fairly well charge batteries

Resistance in the charging circuit (undersized cable, dirty or lose connections)

A passive split charge diode being used.

A blown diode in the alternator.

 

If you can't ascertainment the alternator's rated output post a photo showing the back of it plus something to scale it from and we can have an informed guess.

 

The point is that the proposed Renology combined MPPT and B2B only sends 25A of alternator current to the batteries. So it is not an alternator issue, it is a B2B limitation issue.

[Tony Brooks]

1 minute ago, nicknorman said:

The point is that the proposed Renology combined MPPT and B2B only sends 25A of alternator current to the batteries. So it is not an alternator issue, it is a B2B limitation issue.

 

Thanks, I thought hew as saying that was all he had got from his alternator. My excuse is bad eyes.

[Tony1]

1 hour ago, Jay88 said:

Hi all,

 

Thanks for all the responses, appreciated.

 

After doing some more research I contacted Sterling who advised to have both alternators go to the starter battery then attach their 120A DC-DC charger

at a cost of £717...bit harsh. 

 

Anyway it got me thinking and I found this Renogy 50A DC-DC charger with MPPT for £230 . So maybe I could attach one alternator to the start battery and the solar cables to the DC-DC charger (saves getting a a separate MPPT) noting that the max solar for the system is 660w, which is fine with me as I'm looking at about 600W. After reading the renogy manual, a downside I can see is that when the sun is not around and I need to start the engine to charge the lithiums, I believe I'll only ever get about 25A from the alternator as opposed to about 120A from the sterling DC-DC charger...

 

OR

 

Maybe I simply install the renogy 60A DC-DC charger between the starter and lithiums and keep the 660W solar on a separate system, atb least I'll get about 60A from when I charge the lithiums via the engine...but do I connect 1 or 2 alternators to the start battery??...hmmm

 

Thoughts?

 

Cheers!

 

 

From Nov to Feb inclusive, you'll generally be relying on engine charging for (very roughly) 75% of your daily needs, and 25 amps charging rate means you'll need to do a 3 or 4 hour engine charge every day to replace a typical 100Ah daily power usage. So factor that extra fuel, engine servicing etc in to your costings for the setup, it may make a difference over 5 years.

 

That limitation of 25 amps of engine charging for at least a quarter of the year (winter) would put me off the combined MPPT/B2B charger. 

 

Also, I would advise not buying the Sterling B2B unless you firstly test how much charge your alternators can put out without overheating.

120 amps sounds like a lot for two 80 amp alternators (assuming they both work together equally).

But I'm no expert- if they are good quality then maybe 120 amps will be fine- I'm suggesting that you check first, before spending £700.

I am concerned because I have cheapo alternators and mine is a sort of worst case, but my 90 amp engine alternator can only put out about 40 amps before it starts to get too hot for my liking.  

(Since they normally operate around 60 degrees, I consider them to be getting too hot for comfort when they are over 100 degrees- but some people allow them to get even hotter, and I'm certainly no expert on that either.)

 

You can test out how much charge your alternators can safely put out by using a length of 16mm cable between the lead acid and the lithiums.

You can try different lengths of cable until you find the right length to allow 120 amps through, and check the alternator temp every 5 minutes over a one hour charging run. I must stress they can get hot very very quickly, so when testing it out, you need to check the temp frequently.

 

 

Once you know how much charge they can safely put out, it might help to inform your setup design. 

 

In your situation I would have a separate MPPT, rather than be limited to 25 amps charging rate. 

Having a 60 amp engine charging rate means that during the winter you can top the lithiums up with say 90 mins of engine running, which is a lot better and cheaper than 3 or 4 hours. 

Its expensive, but over say 5-10 years the cost of a dedicated 60 amp B2B charger will be repaid in saved fuel and engine wear. 

 

But even with a 60 amp B2B charger, you might well up needing both alternators to be involved. I tend to doubt that an 80 amp alternator can safely put out 60 amps continuously, based on what I've seen from my cheapo units. 

With both alternators involved, they should be able to put out a combined 60 amps with no overheating, provided that both alternators are working properly.

If like me, you have one alternator that has some kind of fault, the other alternator might end up doing all of the charging, or perhaps most of it, and that is where the risk of overheating comes in. 

 

 

 

[nicknorman]

18 minutes ago, Tony1 said:

 

From Nov to Feb inclusive, you'll generally be relying on engine charging for (very roughly) 75% of your daily needs, and 25 amps charging rate means you'll need to do a 3 or 4 hour engine charge every day to replace a typical 100Ah daily power usage. So factor that extra fuel, engine servicing etc in to your costings for the setup, it may make a difference over 5 years.

 

That limitation of 25 amps of engine charging for at least a quarter of the year (winter) would put me off the combined MPPT/B2B charger. 

 

Also, I would advise not buying the Sterling B2B unless you firstly test how much charge your alternators can put out without overheating.

120 amps sounds like a lot for two 80 amp alternators (assuming they both work together equally).

But I'm no expert- if they are good quality then maybe 120 amps will be fine- I'm suggesting that you check first, before spending £700.

I am concerned because I have cheapo alternators and mine is a sort of worst case, but my 90 amp engine alternator can only put out about 40 amps before it starts to get too hot for my liking.  

(Since they normally operate around 60 degrees, I consider them to be getting too hot for comfort when they are over 100 degrees- but some people allow them to get even hotter, and I'm certainly no expert on that either.)

 

You can test out how much charge your alternators can safely put out by using a length of 16mm cable between the lead acid and the lithiums.

You can try different lengths of cable until you find the right length to allow 120 amps through, and check the alternator temp every 5 minutes over a one hour charging run. I must stress they can get hot very very quickly, so when testing it out, you need to check the temp frequently.

 

 

Once you know how much charge they can safely put out, it might help to inform your setup design. 

 

In your situation I would have a separate MPPT, rather than be limited to 25 amps charging rate. 

Having a 60 amp engine charging rate means that during the winter you can top the lithiums up with say 90 mins of engine running, which is a lot better and cheaper than 3 or 4 hours. 

Its expensive, but over say 5-10 years the cost of a dedicated 60 amp B2B charger will be repaid in saved fuel and engine wear. 

 

But even with a 60 amp B2B charger, you might well up needing both alternators to be involved. I tend to doubt that an 80 amp alternator can safely put out 60 amps continuously, based on what I've seen from my cheapo units. 

With both alternators involved, they should be able to put out a combined 60 amps with no overheating, provided that both alternators are working properly.

If like me, you have one alternator that has some kind of fault, the other alternator might end up doing all of the charging, or perhaps most of it, and that is where the risk of overheating comes in. 

 

The Renology 120A DC DC has a 1/2 current option that can be selected with an external switch, so if 120A proves too much he can change to 60A, or a bit of both eg 120A when the engine bay is cold, 60A when it’s hot.

 

Good point about a fault with a dual alternator setup. As you say, if one alternator develops a fault the other may end up working flat out and have a short life as a consequence. And of course I think the DC DC will continue to pull the 120A even if the alternators aren’t putting out 120A, thus creating a possibility to flatten the starter battery. But none of these budget schemes is perfect.

[Tony1]

19 minutes ago, nicknorman said:

The Renology 120A DC DC has a 1/2 current option that can be selected with an external switch, so if 120A proves too much he can change to 60A, or a bit of both eg 120A when the engine bay is cold, 60A when it’s hot.

 

Good point about a fault with a dual alternator setup. As you say, if one alternator develops a fault the other may end up working flat out and have a short life as a consequence. And of course I think the DC DC will continue to pull the 120A even if the alternators aren’t putting out 120A, thus creating a possibility to flatten the starter battery. But none of these budget schemes is perfect.

 

That half-power option is actually a bit of a godsend in my case, because it turned out my alternators couldn't cope with the 60 amp charge output that the B2Bs were asking for, so I was able to go down to about 30 amps for each B2B, and the alternators seem work really nicely and stay cool even at tickover revs. 

 

But the advantage of testing out the alternators' combined capabilities first is that you can find out if they will be able to safely deliver the 120 amps.

If they can, great- you buy the 120 amp model and in winter you have a super-efficient charging setup.

But if they can't put out a combined 120 amps, the testing means you find about about that limitation before you've spent the £700, and you can get a much cheaper 60 amp  model instead, and spend the difference on a nice MPPT. 

 

Another option is that you might find out the alternators can deliver say 90 amps safely, and in that case you might want to buy two 60 amps B2Bs, and run one of them at half power. The point being that testing it first means you avoid potentially wasting money and you get the best design. 

 

ETA- would a cheap pure sine wave genny be better for winter charging, to save engine running?

And for that matter, is there such a thing as a cheap pure sine genny?

I mention it because it would allow the use of the combined B2B/MPPT unit (which would be a bit cheaper then buying MPPT plus B2B). It would be another way to supplement the 25 amp charge, and that supplement is only really needed in winter. 

 

Edited September 23, 2022 by Tony1

[nicknorman]

My bad, the Renology DC DC is 60A not 120A, so that will be fine with the 2x 80A alternators and at £170 is much better value than the Sterling … IF it does what it says on the tin. (No reason to suspect it doesn’t).

26 minutes ago, Tony1 said:

 

That half-power option is actually a bit of a godsend in my case, because it turned out my alternators couldn't cope with the 60 amp charge output that the B2Bs were asking for, so I was able to go down to about 30 amps for each B2B, and the alternators seem work really nicely and stay cool even at tickover revs. 

 

But the advantage of testing out the alternators' combined capabilities first is that you can find out if they will be able to safely deliver the 120 amps.

If they can, great- you buy the 120 amp model and in winter you have a super-efficient charging setup.

But if they can't put out a combined 120 amps, the testing means you find about about that limitation before you've spent the £700, and you can get a much cheaper 60 amp  model instead, and spend the difference on a nice MPPT. 

 

Another option is that you might find out the alternators can deliver say 90 amps safely, and in that case you might want to buy two 60 amps B2Bs, and run one of them at half power. The point being that testing it first means you avoid potentially wasting money and you get the best design. 

 

 

… or of course for the price of all those rather inefficient Sterling B2Bs you could have a nice proper alternator controller monitoring and limiting alternator temperature…😀

Edited September 23, 2022 by nicknorman

[Tony1]

5 minutes ago, nicknorman said:

My bad, the Renology DC DC is 60A not 120A, so that will be fine with the 2x 80A alternators and at £170 is much better value than the Sterling … IF it does what it says on the tin. (No reason to suspect it doesn’t).

… or of course for the price of all those rather inefficient Sterling B2Bs you could have a nice proper alternator controller…😀

 

Don't remind me!!!

 

But joking aside, with two cheapo single v belt alternators, you would really want two controllers, and that would get expensive. 

The full cost with installation was around  £600 for one controller, so at the time a B2B at £300 seemed to make sense....

 

Edited September 23, 2022 by Tony1

[nicknorman]

2 minutes ago, Tony1 said:

 

Don't remind me!!!

 

But joking aside, with two cheapo single v belt alternators, you would really want two controllers, and that would get expensive. 

The full cost with installation was around  £600 for one controller, so at the time a B2B at £300 seemed to make sense....

 

I think with two identical alternators such as the OP has, one controller operating two alternators would be fine, provided the max field current was within the limits of the device. Since it seems these alternator controllers have a max field current limit of around 10-15A and each alternator probably needs 4.5A max, it should be Ok, but you’d need to check the specifics. In your case you had very different alternators, so you’d need two. Or just ignore the small alternator.

[Tony1]

9 minutes ago, nicknorman said:

I think with two identical alternators such as the OP has, one controller operating two alternators would be fine, provided the max field current was within the limits of the device. Since it seems these alternator controllers have a max field current limit of around 10-15A and each alternator probably needs 4.5A max, it should be Ok, but you’d need to check the specifics. In your case you had very different alternators, so you’d need two. Or just ignore the small alternator.

 

My problem was that even the domestic alternator, although rated at 100 amps, would not put out more than 40-45 amps without getting well over 100 degrees, and I just didnt feel comfortable with that running temperature over the long term. 

So I'd have been looking at spending around £1200 on two controllers plus installation, to achieve a charging rate of maybe 70 amps. 

With what I know now, I would have gone for that, I totally agree its by far the best solution.

But what can I say- back then I was young, foolish, hot-headed and of course impossibly good looking.

 

ETA- joking aside, if the OP can stretch to an alternator controller plus installation, and if it definitely works with his two alternators at once, including running two sets of temp sensors etc (one for each alternator), that would be what I'd go for. Its a lot, but well worth it

Could be worth the OP calling Ed Shiers- if anyone will know about that setup, he will. 

 

Edited September 23, 2022 by Tony1

[Jen-in-Wellies]

On 17/09/2022 at 22:41, nicknorman said:

If doing it on a budget I would have the alternator connected to a smallish LA battery, then from the LA battery via a longish bit of wire to add some resistance and hence limit current, to the Li. Via some sort of battery isolator switch so one could “turn off” charging to the Li. When you do that, the LA can absorb the otherwise damaging alternator voltage transient (in the moment that it takes for the alternator field current to subside). And something like a BMV712 to allow you to keep an eye on the Li SoC so you can shut off charging (manually) before the battery gets rammed fully charged (which is not great for its longevity when done habitually).

With a long wire system for charging a Li bank via a LA battery from an alternator. What sort of wire cross sectional area and length are we talking about to limit current to around 60, or 70A without overheating the wire? Trying to get a feel for what has worked in practice.

 

[nicknorman]

1 hour ago, Jen-in-Wellies said:

With a long wire system for charging a Li bank via a LA battery from an alternator. What sort of wire cross sectional area and length are we talking about to limit current to around 60, or 70A without overheating the wire? Trying to get a feel for what has worked in practice.

 

I'll have a think about it but one relevant factor is the voltage:current profile of the alternator. Hard to know, but knowledge of the rated output of the alternator would be helpful. Perhaps in terms of the % of maximum output that is desired.

 

Looks like 16mm^2 cable could handle 60 or 70A but it depends on the temperature rating of the cable and one would have to ensure that its heat dissipation wasn't restricted by being enclosed or touching itself. Which is a bit dodgy and why this is a "bodge DIY" solution, not an optimally engineered solution! Definitely fused at battery end in case of insulation melting and short circuit, and supported away from metalwork.

 

8m of 16mm^2 cable would drop 0.7v which would probably be about right for a largish alternator, but bear in mind I have never done this so don't sue me! Maybe start with 10m and cut down a bit if necessary

Edited September 27, 2023 by nicknorman

[Jen-in-Wellies]

34 minutes ago, nicknorman said:

I'll have a think about it but one relevant factor is the voltage:current profile of the alternator. Hard to know, but knowledge of the rated output of the alternator would be helpful. Perhaps in terms of the % of maximum output that is desired.

Looks like 16mm^2 cable could handle 60 or 70A but it depends on the temperature rating of the cable and one would have to ensure that its heat dissipation wasn't restricted by being enclosed or touching itself. Which is a bit dodgy and why this is a "bodge DIY" solution, not an optimally engineered solution! Definitely fused at battery end in case of insulation melting and short circuit, and supported away from metalwork.

 

8m of 16mm cable would drop 0.7v which would probably be about right, but bear in mind I have never done this so don't sue me! Maybe start with 10m and cut down a bit if necessary

Thanks. Those are similar to the figures I was guessing/calculating (calcuguessing?!). The alternator is officially 115A, but how much of that is usable in a steady state without overheating is unknown. How much some force ventilation might help, again unknown. Currently it has a Victron 30A battery to battery charger to handle alternator charging of the Lithiums, which has been fine, but the boat concerned is going off grid this winter and upping that charging current would be useful to reduce the amount of engine running needed when the solar becomes useless. I also dislike the bodge DIY approach. Was considering a timer to break a high current relay in the long wire between start and lithium batteries to stop the lithium charge. Could also monitor alternator temperature and lithium voltage too to open the relay, but still very crude. Renogy do a 60A battery to battery charger, with alternator detection and this could be a better option. Putting the Victron batt2batt charger up for sale would probably recoup the cost.

[Tony1]

 

I gave it a go but that was well over two years ago so I can't remember the details reliably. I recall trying out wire that was `16mm sq, and finding that even 8 metres length of it allowed more than 60 amps through.  

I think the one that I found suitable was 10mm sq wire, and I ended up with at least 5-6 metres of it. 

I think I got it set up to allow about 60 amps through, but the wire felt a teeny bit too warm for my liking, and I didn't feel entirely comfortable using it as a routine thing, or having 6+ metres of very warm wire in loops hanging around in the engine bay. 

The problem you have with finding the right length for your setup is that you have to start from a small current and work upwards, because the way you alter the current (when you're testing it out) is by cutting off a length of the wire- and cutting a length off will increase the current flow. 

But then if you buy 15 metres of 10mm sq cable to start off with a low current, you risk wasting 5 metres of that because it might turn out that you only need 10m, or even less.

Maybe you could secure it to a board or around a cylinder somehow, in a way that allowed to add on one metre at a time.

Do give it a good run though, and maybe allow a margin for the alternator getting a bit hotter in summer, if you are doing your testing in freezing weather as I did. 

But I would keep a close eye on the alternator temp though- I was surprised how quickly mine started overheating if it was putting out too much current. 

 

The other (potential) future snag is BSS regs. I recall someone saying that if it happens that future BSS regs come out about lithiums, one of the rules will be that you cant directly connect lead acid and lithiums in parallel setups. It might be that inserting a B2B charger will make it compliant, but that said I dont think there's any certainty about any of this BSS stuff, so its only a possible concern, certainly not a real issue. 

 

 

[Jen-in-Wellies]

2 minutes ago, Tony1 said:

 

I gave it a go but that was well over two years ago so I can't remember the details reliably. I recall trying out wire that was `16mm sq, and finding that even 8 metres length of it allowed more than 60 amps through.  

I think the one that I found suitable was 10mm sq wire, and I ended up with at least 5-6 metres of it. 

I think I got it set up to allow about 60 amps through, but the wire felt a teeny bit too warm for my liking, and I didn't feel entirely comfortable using it as a routine thing, or having 6+ metres of very warm wire in loops hanging around in the engine bay. 

The problem you have with finding the right length for your setup is that you have to start from a small current and work upwards, because the way you alter the current (when you're testing it out) is by cutting off a length of the wire- and cutting a length off will increase the current flow. 

But then if you buy 15 metres of 10mm sq cable to start off with a low current, you risk wasting 5 metres of that because it might turn out that you only need 10m, or even less.

Maybe you could secure it to a board or around a cylinder somehow, in a way that allowed to add on one metre at a time.

Do give it a good run though, and maybe allow a margin for the alternator getting a bit hotter in summer, if you are doing your testing in freezing weather as I did. 

But I would keep a close eye on the alternator temp though- I was surprised how quickly mine started overheating if it was putting out too much current. 

 

The other (potential) future snag is BSS regs. I recall someone saying that if it happens that future BSS regs come out about lithiums, one of the rules will be that you cant directly connect lead acid and lithiums in parallel setups. It might be that inserting a B2B charger will make it compliant, but that said I dont think there's any certainty about any of this BSS stuff, so its only a possible concern, certainly not a real issue. 

 

 

Thanks for that. I was concerned about 10mm2 getting a bit warm, as it is on the limit for current, as recommended by the makers. The cost of experimentation is also a consideration. I wondered about aluminium, or steel, higher resistivity, so shorter length, but then insulation has to be arranged and more BSS worries as it isn't stranded copper wire. I'd say that a B2B charger is more likely to meet future BSS requirements than the long wire method, but who knows? The boat concerned has a B2B already and it now looks like higher current ones are available.

[Tony1]

12 minutes ago, Jen-in-Wellies said:

Thanks. Those are similar to the figures I was guessing. The alternator is officially 115A, but how much of that is usable in a steady state without overheating is unknown. How much some force ventilation might help, again unknown. Currently it has a Victron 30A battery to battery charger to handle alternator charging of the Lithiums, which has been fine, but the boat concerned is going off grid this winter and upping that charging current would be useful to reduce the amount of engine running needed when the solar becomes useless. I also dislike the bodge DIY approach. Was considering a timer to break a high voltage relay in the long wire between start and lithium batteries to stop the lithium charge. Could also monitor alternator temperature and lithium voltage too to open the relay, but still very crude. Renogy do a 60A battery to battery charger, with alternator detection and this could be a better option. Putting the Victron batt2batt charger up for sale would probably recoup the cost.

 

I might have just the thing. 

I switched to using two victron B2Bs a while back, so I have both a 30 amp and a 60amp Sterling B2B sitting idle and available for a very reasonable price. 

These units can be switched to half power, so the 30 amp unit can put out either 15 amps or 26 amps, and the larger unit can put out either 29 amps or 49-50 amps. Using two of them in combination  gave me a lot of flexibility in terms of setting the right current level to keep the alternator cool. 

I could even switch up the current when I was doing a static charge, because if I revved up to say 1300rpm, the alternator would put out more current and stay cool. 

 

If the alternator is a cheap automotive type like on my canaline, I would guess its good for about 45 amps continuous, and if you're static and rev it up and bit, maybe 55 amps at most.  

So in theory the 60 amp Sterling would be ok, as it puts out (in theory) 48-50 amps. BUT the 60 amp sterling unit throttles itself back to half power mode every 10 minutes or so (I think they get a bit too hot), so I found it was more consistent if I ran it full time at half power (about 29 amps), and added in the 30 amp unit. 

 

The problem I had was that if exceeded the optimum safe current for my alternator by even 5 amps or so, the alternator would get really hot really quickly, so I erred on the lower side. 

 

 

 

Edited September 27, 2023 by Tony1

[Jen-in-Wellies]

1 minute ago, Tony1 said:

 

I might have just the thing. 

I switched to using two victron B2Bs a while back, so I have both a 30 amp and a 60amp Sterling B2B sitting idle and available for a very reasonable price. 

These units can be switched to half power, so the 30 amp unit can put out either 15 amps or 26 amps, and the larger unit can put out either 29 amps or 49-50 amps. Using two of them in combination  gave me a lot of flexibility in terms of setting the right current level to keep the alternator cool. 

I could even switch up the current when I was doing a static charge, because if I revved up to say 1300rpm, the alternator would put out more current and stay cool. 

 

If the alternator is a cheap automotive type like on my canaline, I would guess its good for about 45 amps continuous, and if you're static and rev it up and bit, maybe 55 amps at most.  

So in theory the 60 amp Sterling would be ok, as it puts out (in theory) 48-50 amps. BUT the 60 amp sterling unit throttles itself back to half power mode every 10 minutes or so (I think they get a bit too hot), so I found it was more consistent if I ran it full time at half power (about 29 amps), and added in the 30 amp unit. 

 

I wondered about piggy-backing B2B's. Sounds like that is an option. Excellent. More food for thought.

[Tony1]

1 minute ago, Jen-in-Wellies said:

I wondered about piggy-backing B2B's. Sounds like that is an option. Excellent. More food for thought.

 

What I did was to buy an additional 18 amp victron B2B and run it in parallel. That would get your friend up to 30 + 18, so maybe 48 amps?

And tbh even that might be too much current anyway, if its a cheapo alternator. 

My 30 amp Sterling added to the existing Victron might be a good solution. You could add in 15 amps by running it at half power, or if you can keep the revs up at say 1300, you might be able to run it at the full 28/29 amps.

If I had to guess, I'd say 60 amps continuous might be just a bit too much unless its a good quality alternator. 

Plenty of options- but I think its worth doing a wire test anyway to establish how much the alternator can safely put out, before committing any money to buying B2Bs that might pull too much current. Its the alternator capacity that will probably decide what is the best B2B in this setup- and you probably dont want to exceed the safe max by much- as I say, in my case it overheated if I even drew 5 amps over the safe limit. 

 

[Jen-in-Wellies]

1 minute ago, Tony1 said:

 

What I did was to buy an additional 18 amp victron B2B and run it in parallel. That would get your friend up to 30 + 18, so maybe 48 amps?

And tbh even that might be too much current anyway, if its a cheapo alternator. 

My 30 amp Sterling added to the existing Victron might be a good solution. You could add in 15 amps by running it at half power, or if you can keep the revs up at say 1300, you might be able to run it at the full 28/29 amps.

If I had to guess, I'd say 60 amps continuous might be just a bit too much unless its a good quality alternator. 

Plenty of options- but I think its worth doing a wire test anyway to establish how much the alternator can safely put out, before committing any money to buying B2Bs that might pull too much current. Its the alternator capacity that will probably decide what is the best B2B in this setup- and you probably dont want to exceed the safe max by much- as I say, in my case it overheated if I even drew 5 amps over the safe limit. 

 

That sounds sensible. Do some experimentation with the long wire method and a temperature probe on the alternator and/or watch for the smoke(!) and decide on a suitable safe maximum charge current. Complicated by the alternator cooling being speed dependent. May get in touch regarding your Sterling. Thanks again for sharing your real world experience.