Will a DC-to-DC charger protect the alternator from lithium BMS cutoff?

[witzgall]

Chris from Balmar here. The answer is no. If an alternator is running and outputting current when a battery is disconnected, there is a voltage spike as the alternator field collapses. Any DC to Dc converter used may have some over-voltage protection built in to protect ITSELF from this voltage spike, but it would not likely do much to keep the spike from reaching the diodes in the back on the alternator.

We have an Alternator Protection Module coming out soon to address this issue.

Chris

Originally Posted by rgleason

Nobody has answered the question asked by OP in a direct manner!


Will a DC-to-DC charger protect the alternator from lithium BMS cutoff?

The question stands unanswered

[newhaul]

Originally Posted by rgleason

@Newhaul. What does "..let the majic smoke" mean? I need a translation to english please.

Translated: the internals will burn up and the unit will die .

[lmxr]

Originally Posted by sailingharry

[...] To the OP's original concern about protecting the alternator from a disconnect, I wonder if a better solution would be a load that gets switched into the circuit when the engine is running. A simple relay on the ignition switch, that would turn on a load like a light bulb. If you can find an old 100 watt incandescent household bulb, that would draw very little current at 12 volts, but would probably protect the alternator just fine. It would suck down one amp of the alternator output, and disconnect when the engine was off.

I'm sorry but I see it somewhat differently: I think the voltage surge after a battery disconnect is the result of the stator coil in the alternator. The current through a coil is continuous. Therefore, I assume that if the alternator was producing 60 A before the disconnect, it will also be producing 60 A after the disconnect. Not long, just for a millisecond or so.

If you add a load that consumes 1 A of that 60 A, then there would be still 59 A that has to find it's way through the loads. Therefore, I don't think it solves the issue.

One method I've read about is to clamp the surge using a protection device. Sterling makes one for around 65$. Another method is to leave a battery or a large capacitor in the system, for example connected through a charge distributor.

[newhaul]

Originally Posted by sailingharry

A couple of comments / questions.

A response indicated that lithiums are not meant to start engines. I strongly disagree! You can buy off the shelf lithium engine start batteries, but they really aren't any different. And engine cranking load is far less than typical inverter loads, and lithiums are better at high loads than lead acid. A lithium battery makes a perfectly acceptable start battery.

I have a question or concern about charging the AGM and B2B to the lithium. In OP's case, the alternator is fairly weak, and so this might work. But it is often touted as the answer, and on larger installations, mine for instance, with a 200 amp or more alternator source it seems a waste to put a 50 or 100 amp B2B in the line and limit charging to those rates.

With OP's internal regulator, he has a challenge. But with external regulators, it seems to me that it would be far superior to interrupt the field wire then to interrupt the alternator output. You switch 10 amps versus 200, and there is no chance of frying the alternator. Of course, with drop-in solutions, there's almost no opportunity to do this.

To the OP's original concern about protecting the alternator from a disconnect, I wonder if a better solution would be a load that gets switched into the circuit when the engine is running. A simple relay on the ignition switch, that would turn on a load like a light bulb. If you can find an old 100 watt incandescent household bulb, that would draw very little current at 12 volts, but would probably protect the alternator just fine. It would suck down one amp of the alternator output, and disconnect when the engine was off.

But even that answer gets me thinking. When the engine is running, you most assuredly have other things on the boat running. Chart plotter, VHF, stereo, maybe autopilot or running lights, etc. Are these loads not enough to protect the alternator from spiking? Is the concern more theoretical or special case than as widespread as it is thought?

Best solution with a high output alternator for now at least is a programmable external regulator. Or run multiple b2b chargers .

[flightlead404]

Originally Posted by rgleason

@Newhaul. What does "..let the majic smoke" mean? I need a translation to english please.

Its a little known fact, but electrical circuits actually work like plumbing, by piping special smoke around in those little colored tubes we call “wires”

When the pressure (measured in amps or psi) gets too great the pipes or the little valves inside our devices burst and that special smoke escapes. It looks a lot like things burning.

When the smoke gets out things stop working.

[goboatingnow]

Originally Posted by lmxr

I'm sorry but I see it somewhat differently: I think the voltage surge after a battery disconnect is the result of the stator coil in the alternator. The current through a coil is continuous. Therefore, I assume that if the alternator was producing 60 A before the disconnect, it will also be producing 60 A after the disconnect. Not long, just for a millisecond or so.

If you add a load that consumes 1 A of that 60 A, then there would be still 59 A that has to find it's way through the loads. Therefore, I don't think it solves the issue.

One method I've read about is to clamp the surge using a protection device. Sterling makes one for around 65$. Another method is to leave a battery or a large capacitor in the system, for example connected through a charge distributor.

It’s not complex V = L di/dt. So both the magnitude of the current and the time over which it dissipates contributes to the resulting spike.

As I mention almost all modern alternators are rated to IEC standards to withstand load dumps. But they are not rated to do so for more then a few cycles.

But anything that slows the di/dt rate of change will dramatically reduce the resulting voltage.

Using TVS diode etc is a challenge as modern load dumping tests require 200mS survivability which is really hard to achieve.

However as I mentioned I’d investing in lithium sort out a proper alternator disconnect scheme and have the alternator directly charge the lithium’s ( and connect all your other charge sources similarly ). Then use a dc dc ( with manual override ) system to keep the starter topped up.

[goboatingnow]

Originally Posted by sailingharry

A couple of comments / questions.

A response indicated that lithiums are not meant to start engines. I strongly disagree! You can buy off the shelf lithium engine start batteries, but they really aren't any different. And engine cranking load is far less than typical inverter loads, and lithiums are better at high loads than lead acid. A lithium battery makes a perfectly acceptable start battery.

I have a question or concern about charging the AGM and B2B to the lithium. In OP's case, the alternator is fairly weak, and so this might work. But it is often touted as the answer, and on larger installations, mine for instance, with a 200 amp or more alternator source it seems a waste to put a 50 or 100 amp B2B in the line and limit charging to those rates.

With OP's internal regulator, he has a challenge. But with external regulators, it seems to me that it would be far superior to interrupt the field wire then to interrupt the alternator output. You switch 10 amps versus 200, and there is no chance of frying the alternator. Of course, with drop-in solutions, there's almost no opportunity to do this.

To the OP's original concern about protecting the alternator from a disconnect, I wonder if a better solution would be a load that gets switched into the circuit when the engine is running. A simple relay on the ignition switch, that would turn on a load like a light bulb. If you can find an old 100 watt incandescent household bulb, that would draw very little current at 12 volts, but would probably protect the alternator just fine. It would suck down one amp of the alternator output, and disconnect when the engine was off.

But even that answer gets me thinking. When the engine is running, you most assuredly have other things on the boat running. Chart plotter, VHF, stereo, maybe autopilot or running lights, etc. Are these loads not enough to protect the alternator from spiking? Is the concern more theoretical or special case than as widespread as it is thought?

I agree , a relatively small load switched in before output disconnect will dramatically reduce the resulting voltage spike.

It’s a myth you need a battery with an alternator per se. What you primarily need is to avoid abrupt current changes the alternator regulator will happily handle slower changing load demands.

[kmacdonald]

If you have adequate solar you may not need a lot of charging capacity from an alternator. In that case a LA start battery and a B to B charger and stock alternator is a reasonable low cost solution. I know a lot of people want the full charge capacity of a high output alternator but that's a lot more expensive and may not be needed if you have a lot of solar. All situations are different and require different solutions.

[newhaul]

Originally Posted by goboatingnow

I agree , a relatively small load switched in before output disconnect will dramatically reduce the resulting voltage spike.

It’s a myth you need a battery with an alternator per se. What you primarily need is to avoid abrupt current changes the alternator regulator will happily handle slower changing load demands.

And how do you propose to accomplish a charging demand without having a battery in the loop

[newhaul]

Ok just went over the entire thread and noticed one thing . The op has not been back to post since starting the thread.
Secondly and this is the biggie nobody ( not even me ) has stated any size of LFP bank that is being discussed.

We do need to know that to give reasonable possible solutions to the issue posted about .

Mine is a 250AH LFP bank so 50 amps out of my alternator is about the perfect power point . For longevity. A b2b is well within that range
Now if he has a 1k ah bank then no its not a good fit.

[sailingharry]

Originally Posted by newhaul

Mine is a 250AH LFP bank so 50 amps out of my alternator is about the perfect power point . For longevity. A b2b is well within that range
Now if he has a 1k ah bank then no its not a good fit.

Newhaul, I do not yet have lithium, and am intending to do it the winter of 22/23. I am learning a lot, but do not have personal experience yet. Your comment on the charge rate though concerns me. I thought one of the benefits of lithium was high charge rates. I currently have 800 AH of AGM, and when down 200 or 300 AH can push 180 to 200 amps for an hour. I would replace that 800 AH with about 400 to 500. You seem to be suggesting that I would limit my charge rate to under 100 amps, which would be troubling to say the least!

Thoughts?

[newhaul]

Originally Posted by sailingharry

Newhaul, I do not yet have lithium, and am intending to do it the winter of 22/23. I am learning a lot, but do not have personal experience yet. Your comment on the charge rate though concerns me. I thought one of the benefits of lithium was high charge rates. I currently have 800 AH of AGM, and when down 200 or 300 AH can push 180 to 200 amps for an hour. I would replace that 800 AH with about 400 to 500. You seem to be suggesting that I would limit my charge rate to under 100 amps, which would be troubling to say the least!

Thoughts?

Sorry I should expand on that. A .25C to .3C are best rates for extended longevity.
But banks can charge up to 1C depending on manufacturer specifications.

Explanation is like my 250ah best longevity would mean a 50 to 60 amp input charging.
But if needed it can accept 250 amps .
.5 is commonly recommended by manufacturers. For my bank that's 125 amps

Now by longevity we are talking at 1C 2500 cycles . At .5C 3500. And at my .25 preferred we are expecting in excess of 7,000 full cycles . For my cells .

[mitiempo]

Originally Posted by witzgall

Chris from Balmar here. The answer is no. If an alternator is running and outputting current when a battery is disconnected, there is a voltage spike as the alternator field collapses. Any DC to DC converter used may have some over-voltage protection built in to protect ITSELF from this voltage spike, but it would not likely do much to keep the spike from reaching the diodes in the back on the alternator.

Chris

The answer is yes.

If the DC to DC converter is wired as designed - from battery to battery - it will work well. The alternator should be wired to the start battery which it will always see regardless of the DC to DC's output. The alternator will not suffer.

The start battery should be either Fla or Agm. The savings of not having a LiFePo4 start battery will more than cover the cost of a Victron Orion DC to DC charger.

The op has an outboard so a Balmar alt and 614 isn't an option, even if he isn't on a budget.

[HankOnthewater]

OK we have here two opposing answers from two CF members (Witzgall and Mitiempo), both I believe to be experts in this field. This disagreement does not make sense to me, even scares me to think "if the experts disagree, what hope do us mere mortals have?"
I do not know the electrical prowess of the other contributors, except for Goboatingnow, another expert.

This discrepancy, 'yes' vs 'no' that alternator will be damaged if the BMS shuts off..... is that a 'yes' if there is no LFA battery between alternator and LFP bank?
and is that a 'no', if there is such LFA battery?

Maybe I am hijacking the thread, but original poster has not come back....
I just purchased LFP bank for my small campervan (Calb with Daly), with a bit of solar (Victron controller) and and a Victron DC to DC charger from the engine/van battery. No issues there... I hope.

But for my boat the setup is much larger, and have 2 Balmar alternators (90 amp and 250 amp) charge the current ship's AGM batteries directly with a Balmar 614 and the other regulator is a Max Charge I think or a 512, all Balmar. The starter battery is charged with with a small DC to DC charger.

Creating some smoke there would be very inconvenient to say at least, also in terms of dollars.

Obviously if I had a ship's battery bank of LFP, then if the BMS would stop the charging/cuts off, alternators would smoke. Here is the question: What do I need to do to prevent that happening?

[newhaul]

Originally Posted by mitiempo

The answer is yes.

If the DC to DC converter is wired as designed - from battery to battery - it will work well. The alternator should be wired to the start battery which it will always see regardless of the DC to DC's output. The alternator will not suffer.

The start battery should be either Fla or Agm. The savings of not having a LiFePo4 start battery will more than cover the cost of a Victron Orion DC to DC charger.

The op has an outboard so a Balmar alt and 614 isn't an option, even if he isn't on a budget.

Not correct wrt the question presented by the op .

The answer is no it wouldn't if there is no battery between the alternator and the b2b.