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Old 03-18-2022, 05:07 PM   #1
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Load dump - Lifepo4 - Generator - battery charger

Questions for now but after reading several posts here and reading marine how to articles about alternators and lifepo4 it seems that alts get hit with a fatal load dump spike if the BMS disconnects.

My first question would be, what is in place to protect the generator if the same thing happens?
Could it be that this will not happen as it's the inverter/charger programming that does the shutdown and not the BMS?
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Old 03-18-2022, 05:35 PM   #2
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I noticed when on the hard and connected to shore power when the LFP bank was fully charged it went into 27.2v "float" - there was no disconnect by BMS.

Why do the alternator charge options have this happen?
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Old 03-18-2022, 05:44 PM   #3
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I had a Sterling Alternator Protection Device for our last boat in case the BMS shutdown the batteries while the alternator was charging them.
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Old 03-18-2022, 05:56 PM   #4
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A sudden load drop won't hurt a generator. With an alternator it's the output diodes that get hurt if the output gets totally disconnected (a sudden load change without a total disconnect won't hurt though). A generator doesn't have those, so it's just a question of how fast the voltage regulator and governor respond and how much of a voltage and frequency spike you'll get on the output.

If you keep the voltage regulated appropriately during charging, you shouldn't normally get a disconnect. You still want to protect and alternator against it just in case.
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Old 03-18-2022, 06:04 PM   #5
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A sudden load drop won't hurt a generator. With an alternator it's the output diodes that get hurt if the output gets totally disconnected (a sudden load change without a total disconnect won't hurt though). A generator doesn't have those, so it's just a question of how fast the voltage regulator and governor respond and how much of a voltage and frequency spike you'll get on the output.
Good to know and I learned something new
But if the charger that the generator is running through is set up correctly the battery won't overcharge so BMS won't come into play.

The Charger is essentially the first line of defence.

Wouldn't it make sense then to have charging done via an actual charger vs expensive alternators and what seems to me to be, issues?

I know many are advocates for DC - DC chargers from starts, but I am yet to find one of those that puts out much in the way of amps.
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Old 03-18-2022, 06:08 PM   #6
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I had a Sterling Alternator Protection Device for our last boat in case the BMS shutdown the batteries while the alternator was charging them.
But why is the BMS even coming into play?
Surely all that expensive balmar/sterling stuff should have something that regulates the charge when batts hit a programmable voltage?
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Old 03-18-2022, 06:10 PM   #7
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Good to know and I learned something new
But if the charger that the generator is running through is set up correctly the battery won't overcharge so BMS won't come into play.

The Charger is essentially the first line of defence.

Wouldn't it make sense then to have charging done via an actual charger vs expensive alternators and what seems to me to be, issues?

I know many are advocates for DC - DC chargers from starts, but I am yet to find one of those that puts out much in the way of amps.
An appropriately regulated alternator would achieve the same. I agree on the lack of good DC-DC chargers in big sizes. Protecting the alternator can be simple. A small lead acid battery connected to the output (or use the starting battery) and an ACR will do the trick. The lead acid won't get an ideal charge (and may get over absorbed), but if the BMS does disconnect the alternator output isn't disconnected and the diodes won't get zapped.

Ideally the situation will never come up, but it's good to know the alternator will live if something does cause a BMS disconnect with the engine running.
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Old 03-18-2022, 06:27 PM   #8
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An appropriately regulated alternator would achieve the same.
.
But at what cost?
For example, how much would one need to spend on alts and extras to match our existing 120amp @ 24v charger output?

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I agree on the lack of good DC-DC chargers in big sizes.
tis' unfortunate

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Protecting the alternator can be simple. A small lead acid battery connected to the output (or use the starting battery) and an ACR will do the trick. The lead acid won't get an ideal charge (and may get over absorbed), but if the BMS does disconnect the alternator output isn't disconnected and the diodes won't get zapped.

Ideally the situation will never come up, but it's good to know the alternator will live if something does cause a BMS disconnect with the engine running
We had a Victron VSR (same as an ACR???) when we had the AGM bank
Still managed to kill off 2 large frame alts but that would have been overworking a "continuosly rated" alt not a voltage spike
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Old 03-18-2022, 06:35 PM   #9
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Depending on the alternator in question, some can have an external regulator added easily without having to buy an extensive alternator. Most alternators will need their output limited to avoid cooking if they're charging a big enough battery bank.
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Old 03-18-2022, 06:54 PM   #10
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. Most alternators will need their output limited to avoid cooking if they're charging a big enough battery bank.
So.......not really a suitable option imho, especially when looking at the cost.

In Oz it'd be around $2400 for an alt
https://www.outbackmarine.com.au/j18...-alternator-wi

And $700 for the reg
https://www.outbackmarine.com.au/mul...cludes-harness
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Old 03-18-2022, 07:00 PM   #11
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Which gets me back to something I have mentioned before but had no real response to.

Why not use the existing charger onboard and connect a 3.5kva generator head to it?

(Below is a Mecc Alte head as an example)
https://www.ebay.com/itm/Mecc-Alte-3...edirect=mobile

Online calculators allow you to choose a pulley suited to cruise rpm
Sure, you'll get nothing at idle but once underway you'll be smashing the amps in , continually and doing it for hundreds of dollars, not thousands.

Continual power at cruise rpm
Low cost
No BMS disconnect as running through the inverter/charger

Am I missing something?
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Old 03-18-2022, 07:02 PM   #12
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But why is the BMS even coming into play?
Surely all that expensive balmar/sterling stuff should have something that regulates the charge when batts hit a programmable voltage?

It's strictly a failure condition. In a correctly operating system, the BMS will never disconnect the battery. If it does, it's because something went wrong and a charger has run amuck, assuming it's an overcharge issue. The BMS disconnect is an action of last resort to keep the battery from becoming dangerously overcharged. And if that happens when an alternator is running at high output, that's where the problem arises.


When the alternator is running at high output and the battery suddenly disconnects, all you are left with are the house loads. That will likely be a big change in load, and that rapid change in alternator load causes a voltage spike, and that spike can be damaging to attached loads and to the alternator itself.


One solution, and really the only solution for internal BMS products, is some sort of clamping diode that limits the voltage spike. With an external BMS, and hopefully internal BMSes in the future, the BMS provides a signal of impending BMS disconnect and that can be used to shut off the alternator.


Hope that helps explain it.
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Old 03-18-2022, 07:05 PM   #13
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Which gets me back to something I have mentioned before but had no real response to.

Why not use the existing charger onboard and connect a 3.5kva generator head to it?

(Below is a Mecc Alte head as an example)
https://www.ebay.com/itm/Mecc-Alte-3...edirect=mobile

Online calculators allow you to choose a pulley suited to cruise rpm
Sure, you'll get nothing at idle but once underway you'll be smashing the amps in , continually and doing it for hundreds of dollars, not thousands.

Continual power at cruise rpm
Low cost
No BMS disconnect as running through the inverter/charger

Am I missing something?

I think I answered this in the other thread where you brought it up. Yes, you could do it. The down side is that there would only be one engine RPM where it would produce usable power at 50hz or 60hz, and even then it would be poorly regulated. But if that's acceptable to you...
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Old 03-18-2022, 07:07 PM   #14
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But why is the BMS even coming into play?
Surely all that expensive balmar/sterling stuff should have something that regulates the charge when batts hit a programmable voltage?

It's strictly a failure condition. In a correctly operating system, the BMS will never disconnect the battery. If it does, it's because something went wrong and a charger has run amuck, assuming it's an overcharge issue. The BMS disconnect is an action of last resort to keep the battery from becoming dangerously overcharged. And if that happens when an alternator is running at high output, that's where the problem arises.


When the alternator is running at high output and the battery suddenly disconnects, all you are left with are the house loads. That will likely be a big change in load, and that rapid change in alternator load causes a voltage spike, and that spike can be damaging to attached loads and to the alternator itself.


One solution, and really the only solution for internal BMS products, is some sort of clamping diode that limits the voltage spike. With an external BMS, and hopefully internal BMSes in the future, the BMS provides a signal of impending BMS disconnect and that can be used to shut off the alternator.


Hope that helps explain it.
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Old 03-18-2022, 07:16 PM   #15
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I think I answered this in the other thread where you brought it up. Yes, you could do it. The down side is that there would only be one engine RPM where it would produce usable power at 50hz or 60hz, and even then it would be poorly regulated. But if that's acceptable to you...
You did, sort of and were the single responder
I was hoping to get more input in this seperate thread.

The only one RPM I am fine with
We do 99% of our miles at one RPM
Generators do 100% of their running at one RPM

But poorly regulated?
What do you mean by that?
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Old 03-18-2022, 07:40 PM   #16
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You did, sort of and were the single responder
I was hoping to get more input in this seperate thread.

The only one RPM I am fine with
We do 99% of our miles at one RPM
Generators do 100% of their running at one RPM

But poorly regulated?
What do you mean by that?

Frequency regulation will be only as good as the governor on your engine. Propulsion engines usually allow for more droop than a generator governor.


Also generators have some sort of voltage regulation. I don't know what the unit you linked requires, if anything, and how tightly it will regulate voltage.


I really don't know how much of an issue either of these might be, but they are the things I'd worry about and want to look into further.
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Old 03-18-2022, 08:07 PM   #17
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Frequency regulation will be only as good as the governor on your engine. Propulsion engines usually allow for more droop than a generator governor.


Also generators have some sort of voltage regulation. I don't know what the unit you linked requires, if anything, and how tightly it will regulate voltage.


I really don't know how much of an issue either of these might be, but they are the things I'd worry about and want to look into further.

But if we can get these addressed (I'll call Oz supplier on Monday and ask) it sounds like it'll be a far superior source of charging on passage than $3 grand worth of alternator that wants to limit the output because it can't handle the work.
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Old 03-18-2022, 08:23 PM   #18
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It shouldn't take a $3000 alternator to do the job. Any unit that you can access the field terminals to change out the regulator for an external one will do. Then it's just a matter of keeping it cool and putting a temp sensor on it to get as much output as possible.
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Old 03-18-2022, 09:31 PM   #19
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It shouldn't take a $3000 alternator to do the job. Any unit that you can access the field terminals to change out the regulator for an external one will do. Then it's just a matter of keeping it cool and putting a temp sensor on it to get as much output as possible.

I have seen nothing in an alternator that can smash out 140 amps @ 24v continually or anything close to it for less.

Perhaps you can point me in the right direction?

I did see a BIM that'll give 15 minutes on, 20 minutes off
But only in 12v can't find anything like it in 24v and as it spends more time off than on even bigger alts again would be needed
https://battlebornbatteries.com/prod...ation-manager/
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Old 03-18-2022, 09:57 PM   #20
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That quantity of power might be best done with 2 alternators. Stuff that can cool well enough to make that kind of power continuously is going to be hard to come by. But stuff that can do half of that is easier and should be much cheaper even if you need 2 of them.
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