How to deal with the alternator?!

[s/v Jedi]

Someone asked me how I deal with the alternator, so I’m posting about that here. The question concerns on damaging the alternator when a LiFe BMS disconnects from the positive busbar, sending a surge through the system which is likely to blow up the diodes in the alternator.

I already posted our diagram before but attach it here again because it shows what we’re talking about.

My solution is disappointingly simple: I avoid the problem by using AGM starter batteries and DC-DC converters. This means that the surge never happens. I have two Victron 12>24V converters which can take up to 60A alternator output and use that to charge the LiFe house bank.

If you have a 12V house bank you can do the same using 12>12V converter(s) which do the conversion of charge method.

The alternative is to stop the alternator before the disconnect happens. This means you need access to the field wire of the alternator and a BMS that can send a warning signal that you use to activate a relay which disconnects the field wire. Some battery switches can do the same thing. This method is similar to mine: you prevent the disconnect by stopping charging just before the event

[GordMay]

Another strategy is to use a Zap-Stop Diode, installed between alternator's positive output and ground.
Balmar TSP-12/24 (Fused Zap-Stop Diode) ➥ https://shop.pkys.com/Balmar-TSP-24-...ts_p_3639.html

[witzgall]

Chris from Balmar here. Our TSP, transient Spike Protector, Will NOT protect an alternator from battery disconnects. It is designed to protect from voltage transients from things like starter motors, etc.

Chris

Originally Posted by GordMay

Another strategy is to use a Zap-Stop Diode, installed between alternator's positive output and ground.
Balmar TSP-12/24 (Fused Zap-Stop Diode) ➥ https://shop.pkys.com/Balmar-TSP-24-...ts_p_3639.html

[goboatingnow]

couple of beefy Zener Diodes would also do the job, but field manipulation is best

[GordMay]

Originally Posted by witzgall

Chris from Balmar here. Our TSP, transient Spike Protector, Will NOT protect an alternator from battery disconnects. It is designed to protect from voltage transients from things like starter motors, etc.

Thanks for that important caution (correction), Chris.
Does your TSP not include a zener diode, as decribed Here? ➥ https://www.cruisersforum.com/forums...tml#post315900

[s/v Jedi]

If you prefer to just let the surge happen then you can try to fight it using this gadget from Sterling Power: https://shop.marinehowto.com/product...tection-device

It may even protect other sensitive devices like electronics etc.

[markcouz]

Originally Posted by goboatingnow

couple of beefy Zener Diodes would also do the job, but field manipulation is best

I believe that Jedi's "disappointingly simple" solution is the best - why throw dodgy diodes and other finicky electronicse at a bulletproof solution?

[s/v Jedi]

Originally Posted by markcouz

I believe that Jedi's "disappointingly simple" solution is the best - why throw dodgy diodes and other finicky electronicse at a bulletproof solution?

When you want LTO cells for starting service I’m eying those so even though I have AGM’s now, I bought a new alternator with external regulator that supports Lithium

[markcouz]

Originally Posted by s/v Jedi

When you want LTO cells for starting service [emoji3] I’m eying those so even though I have AGM’s now, I bought a new alternator with external regulator that supports Lithium [emoji2]

I am keeping my 24v lead acid bank for high current jobs (start, windlass, future thruster), but use a similar setup to you to charge 12v 400ah lithium bank (24v - mppt - 12v), works very well.

[tanglewood]

Originally Posted by markcouz

I believe that Jedi's "disappointingly simple" solution is the best - why throw dodgy diodes and other finicky electronicse at a bulletproof solution?

I think it's a great approach provided the alternator capacity is within the scope of the DC-DC converters. But when you get to order 200A alternators, and perhaps multiple alternators, the DC-DC approach starts to fall apart and some sort of alternator control starts to look a lot better.


Speaking of which, wouldn't it be nice if the "drop-in" battery manufacturers provided a signal saying that a disconnect is imminent? It would seem so easy to do, and solve so many problems for people who want to utilize the control.

[rgleason]

Originally Posted by tanglewood

..wouldn't it be nice if the "drop-in" battery manufacturers provided a signal saying that a disconnect is imminent? It would seem so easy to do, and solve so many problems for people who want to utilize the control.

I vote for this!!! A set of dry contacts NO/NC

Then you could
1. Run the alternator field wire through it.
2. Control an external relay for parallel FLA battery installations.
3. Avoid frying rectifiers, alternators and other things.

Would this get more complicated with paralleled LiFePo4 +BMS and two sets of contacts?

[s/v Jedi]

Originally Posted by rgleason

I vote for this!!! A set of dry contacts NO/NC

Then you could
1. Run the alternator field wire through it.
2. Control an external relay for parallel FLA battery installations.
3. Avoid frying rectifiers, alternators and other things.

Would this get more complicated with paralleled LiFePo4 +BMS and two sets of contacts?

No, you just use the NC contacts and put them all in series with the field current wire.

[Pitchondesign]

To prevent damage from a BMS disconnect, is it possible to use a Ultra Capacitor battery instead of a DC-DC converter to an AGM? Ultra Capacitor batteries have no charge profile to deal with unlike AGMs, and are as simple as it gets, and can take large current surges. Ultra Capacitor batteries are made in 12v drop in versions. I haven't looked for 24v. Just a thought.

[s/v Jedi]

Originally Posted by Pitchondesign

To prevent damage from a BMS disconnect, is it possible to use a Ultra Capacitor battery instead of a DC-DC converter to an AGM? Ultra Capacitor batteries have no charge profile to deal with unlike AGMs, and are as simple as it gets, and can take large current surges. Ultra Capacitor batteries are made in 12v drop in versions. I haven't looked for 24v. Just a thought.

For what reason? I think capacitors only make sense when you want a -lot- of current for a very short time, like the bass power amplifier in car audio, but for 12V service on a boat, coupled to an engine mounted alternator, a starting service battery makes more sense imho. AGM is pretty happy at a high SOC so seems a better fit than a capacitor.

[Pitchondesign]

Originally Posted by s/v Jedi

For what reason? I think capacitors only make sense when you want a -lot- of current for a very short time, like the bass power amplifier in car audio, but for 12V service on a boat, coupled to an engine mounted alternator, a starting service battery makes more sense imho. AGM is pretty happy at a high SOC so seems a better fit than a capacitor.

The ultra capacitor eliminates the need for the dc-dc charger. Other than that, no advantage. I was thinking in terms of a 12v lithium only system, where start and house banks are lithium. In such a system a small ultra cap battery would provide better protection than a zap stop diode or the Sterling system, both of which can be blown without any indication.