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Old 21-09-2023, 07:35   #1
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Question System redesign to drop in LFP

Although my aging (7 year?) Firefly battery bank is doing well, I can see my future is not in lead. I know moving to a "drop in" LFP will require some system redesign. I would like to have some basic knowledge before doing this, or hiring someone to do it.

I have read everything on marinehowto site, especially https://marinehowto.com/drop-in-life...ated-consumer/

I understand the need to mitigate a BMS dump to save the alternator.. but I have some basic questions..

If the built in BMS disconnects because the batteries get full, how do I prevent everything in the boat from shutting off, like GPS, radar, everything.. If they are connected to the LFP bank, then it disconnects, it, according to my small money brain, will shut everything off, as it is connected to the house/LFP bank.

Which system design would be better, in the above link, RC mentions using a Low Volt-drop FET Isolators or a DC-DC charger. Would using either of these prevent the house load from shutting off if the BMS dumps? Which design would be better for a small simple system. (2 group 31 batteries, no AC power or inverters. see attachment)

Is there still need of a battery switch to combine the battery systems in case of emergency ? For example to use the LFP house bank to start the engine in case the starting battery dies. Or how do I start the engine if the starting battery dies.
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Old 21-09-2023, 07:44   #2
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Re: System redesign to drop in LFP

BMS would only ever shutdown your batteries if the charge sources aren't programmed correctly! It should NEVER happen and I look at my BMS in the same regard as a fuse that should never blow.

When I changed from my failed FF last Dec to $300/100ah drop in batteries all I changed were the alternator regulator programing, the solar absorption voltage and the charged the battery charger to a Gel setting.
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Old 21-09-2023, 07:49   #3
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Re: System redesign to drop in LFP

Quote:
Originally Posted by phantomracer View Post
If the built in BMS disconnects because the batteries get full, how do I prevent everything in the boat from shutting off, like GPS, radar, everything.. If they are connected to the LFP bank, then it disconnects, it, according to my small money brain, will shut everything off, as it is connected to the house/LFP bank.
Ah, yes its a problem isn't it. If you are willing to ignore RC for the moment and we will also over look the ABYC advice, (both linked btw) the solution is a hybrid bank of lead acid (LA) and LifePO4 (LFP).

Now in the US this is almost heresy, but spend some time thinking about it and you might come round to an interesting solution. BMS shuts down because its full, fine. LA carries on supplying light loads. Heavy load applied BMS connects in LFP and supplies power for the likes of a kettle etc.

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Old 21-09-2023, 08:13   #4
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Re: System redesign to drop in LFP

Quote:
Originally Posted by sailorboy1;3825090[COLOR="Red"
]BMS would only ever shutdown your batteries if the charge sources aren't programmed correctly[/COLOR]! It should NEVER happen and I look at my BMS in the same regard as a fuse that should never blow.

When I changed from my failed FF last Dec to $300/100ah drop in batteries all I changed were the alternator regulator programing, the solar absorption voltage and the charged the battery charger to a Gel setting.
That's what I was thinking. However, talking to Balmar tech support, they mentioned it is possible, if the LFP batteries are fully charged, that during initial bulk charge on start up, which is a min of 6 minutes, could be enough to trip the BMS on occasion, even if programmed properly.
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Old 21-09-2023, 08:29   #5
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Re: System redesign to drop in LFP

Quote:
Originally Posted by Pete7 View Post
Ah, yes its a problem isn't it. If you are willing to ignore RC for the moment and we will also over look the ABYC advice, (both linked btw) the solution is a hybrid bank of lead acid (LA) and LifePO4 (LFP).

Now in the US this is almost heresy, but spend some time thinking about it and you might come round to an interesting solution. BMS shuts down because its full, fine. LA carries on supplying light loads. Heavy load applied BMS connects in LFP and supplies power for the likes of a kettle etc.

Pete
Balmar suggested this too, but did not get into too much detail

If I read it right, RC mentions it using an isolator where it won't charge the LFP bank directly (about half way down https://marinehowto.com/drop-in-life...ated-consumer/)
Quote:
A good technique to mitigate load dumps is to keep a buffer “load” on the charge bus at all times (Buffer load = lead acid battery on the systems charge bus (see the Victron ARGOFET Isolator wiring below).


Unless you suggest the LFP batteries joined in parallel with a FLA battery directly

alternatively RC suggests charging the starting battery then using a DC to DC charger to charge the house LFP bank (but slower charging)

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Old 21-09-2023, 09:17   #6
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Re: System redesign to drop in LFP

If you’re building a mission critical power system based on LFP, you need to design it so that BMS disconnects will never occur. In the case of standalone drop-ins, this means that you’ll need to sacrifice a certain portion of your capacity as a buffer. That’s the price for using cheap standalones. BMS disconnects should never, ever happen.

In my boat, in the 18 months we’ve had our LFP system, we’ve never once come close to a disconnect. The bank charges via solar, shore power, and alternator. But that’s largely because we’re running a fully integrated system. All charging sources are under the control of the BMS.
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Old 21-09-2023, 09:59   #7
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Re: System redesign to drop in LFP

On my LFP setup I have the Charge Enable/Disable output from the Victron VE.bus BMS connected to the IGN. input of the Balmar 614 regulator (through a solid state relay). If the BMS signals to disable charge then the Balmar is turned off and alternator output is disabled. I'm not sure this has ever happened though since the Balmar is programmed for 14.1 v and the trip point for the BMS appears to be cell voltage >4v. I guess in the case of 'Drop In' LFP you don't have externally available charge disable output so it's possible that if BMS in battery triggers you will lose DC power. As others have said, it should not happen if charging devices are properly programmed.

I do have a separate start battery that is charged via a Balmar Duo charge from house bank. There is a battery switch that connects either start battery or house bank to starter for emergency start from house bank.

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Old 21-09-2023, 10:03   #8
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Re: System redesign to drop in LFP

Going to your second question, how do you start your engine if the starting battery dies?


Its a good question. I have a LFP/LA system in the RV, where the two battery types are connected by a voltage sensitive relay with an override switch that can disconnect them or force a connection. I have not had the starter battery die yet, probably because most days the RV sits without running I force the connection to maintain the starter battery with the RV solar bank. I also disconnect manually after a few hours when I am driving down the highway and the dumb alternator might overcharge the LFP.

I anticipate a problem with starting the boat engine from the LFP bank. The starter requires several hundred amps, and if you had only two drop in LFP batteries in parallel as your house bank, the BMS could disconnect due to overcurrent. I carry a handheld lithium starter pack for that eventuality.

The only time in 3 years the LFP battery BMS tripped off was when I tried to use it to start a frozen genset. The 130 amp BMS disconnected on overcurrent, but came back on in 5 seconds.
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Old 21-09-2023, 10:10   #9
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Re: System redesign to drop in LFP

First, if the BMS cuts off because of overcharge/high voltage, that stops further charging, but you can still discharge. All drop in batteries work this way. So you don't need to worry about losing power.

Second, it only happens if there is a fault. During normal operation, your chargers will stop charging before the battery reaches the cutoff voltage.

Third, if it does happen (that is, a high voltage cutoff because the battery is full) the charge current is likely to be low, because the battery is full. So an alternator dump is unlikely. That isn't to say it can't or won't happen. I would expect it to happen when people set the high voltage cutoff very low thinking that will extend battery life. And I would expect it to happen if charging was stopped abruptly when the battery isn't full-I.E. charging with high current.

With that knowledge and looking at your current installation drawing, you have a few easy options.

I am trying to remember if the duocharge is current limiting. I believe it is. It doesn't have multistage charging like a DCDC charger, but I think it will limit current to 30 Amps or something. In that case, simply leaving your alternator switch in position 2, so that the alternator charges the start battery, and the duocharge charges the house, will protect you from an alternator load dump. You could do that without changing anything, and use any drop in battery. This is essentially the LFP with Lead-Acid and an isolator mentioned previously. You are using the Duocharge as an isolator, or you could directly replace it with an argofet for more charging current and not be limited to 30A

Another option, you have the balmar regulator, which can be shut off by an external signal. A few drop in batteries are starting to come to market that support this. Or, you could swap the balmar for a wakespeed, or the new arco regulator which isn't released yet but looks promising. Then the alternator could be shut down via CAN bus, which more batteries support.

The difference between using an isolator like the Argo, or a DCDC charger, is that the Argo allows full charge current to the LFP bank. This charges much faster, but if you have a small alternator with an internal regulator, will burn up the alternator. This doesn't seem to apply to you, because you have the balmar 614. The DCDC would in addition to providing isolation would limit current, so the alternator doesn't burn up from being overloaded for long periods.
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Old 21-09-2023, 11:16   #10
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Re: System redesign to drop in LFP

Quote:
Originally Posted by wholybee View Post
First, if the BMS cuts off because of overcharge/high voltage, that stops further charging, but you can still discharge. All drop in batteries work this way. So you don't need to worry about losing power.

Second, it only happens if there is a fault. During normal operation, your chargers will stop charging before the battery reaches the cutoff voltage.

Third, if it does happen (that is, a high voltage cutoff because the battery is full) the charge current is likely to be low, because the battery is full. So an alternator dump is unlikely. That isn't to say it can't or won't happen. I would expect it to happen when people set the high voltage cutoff very low thinking that will extend battery life. And I would expect it to happen if charging was stopped abruptly when the battery isn't full-I.E. charging with high current.

With that knowledge and looking at your current installation drawing, you have a few easy options.

I am trying to remember if the duocharge is current limiting. I believe it is. It doesn't have multistage charging like a DCDC charger, but I think it will limit current to 30 Amps or something. In that case, simply leaving your alternator switch in position 2, so that the alternator charges the start battery, and the duocharge charges the house, will protect you from an alternator load dump. You could do that without changing anything, and use any drop in battery. This is essentially the LFP with Lead-Acid and an isolator mentioned previously. You are using the Duocharge as an isolator, or you could directly replace it with an argofet for more charging current and not be limited to 30A

Another option, you have the balmar regulator, which can be shut off by an external signal. A few drop in batteries are starting to come to market that support this. Or, you could swap the balmar for a wakespeed, or the new arco regulator which isn't released yet but looks promising. Then the alternator could be shut down via CAN bus, which more batteries support.

The difference between using an isolator like the Argo, or a DCDC charger, is that the Argo allows full charge current to the LFP bank. This charges much faster, but if you have a small alternator with an internal regulator, will burn up the alternator. This doesn't seem to apply to you, because you have the balmar 614. The DCDC would in addition to providing isolation would limit current, so the alternator doesn't burn up from being overloaded for long periods.
Thank you...

Quote:
First, if the BMS cuts off because of overcharge/high voltage, that stops further charging, but you can still discharge.
I thought the BMS in a drop in is 'dumb' and just shut the battery down all together (see RC's pic below)? if the BMS cuts off due to being 'full' or high voltage, it will still provide power out?



the 2 options you mention, I believe, is my question.. use a dc to dc charger like duo charge. RC mentions sterling/victron ...to charge the starting battery and use the dc2dc charger to charge the house/LFP bank (like pics in my last comment)
or use the Argo to charge both (I assume it is a type of combiner to use simple terms? which disconnects when there is no charge load? ), and having the FLA battery in the system should keep the house/LFP bank from shutting down. do I understand that correctly?

I think you see my question.. is to mitigate 2 problems - protecting the alternator, and keeping everything powered up at the same time.
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Old 21-09-2023, 11:18   #11
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Re: System redesign to drop in LFP

Quote:
Originally Posted by hjohnson View Post
If you’re building a mission critical power system based on LFP, you need to design it so that BMS disconnects will never occur. In the case of standalone drop-ins, this means that you’ll need to sacrifice a certain portion of your capacity as a buffer. That’s the price for using cheap standalones. BMS disconnects should never, ever happen.

In my boat, in the 18 months we’ve had our LFP system, we’ve never once come close to a disconnect. The bank charges via solar, shore power, and alternator. But that’s largely because we’re running a fully integrated system. All charging sources are under the control of the BMS.
Yes, that is what I am trying to figure out the best way to do that
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Old 21-09-2023, 11:21   #12
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Re: System redesign to drop in LFP

Quote:
Originally Posted by maine-cruiser View Post
On my LFP setup I have the Charge Enable/Disable output from the Victron VE.bus BMS connected to the IGN. input of the Balmar 614 regulator (through a solid state relay). If the BMS signals to disable charge then the Balmar is turned off and alternator output is disabled. I'm not sure this has ever happened though since the Balmar is programmed for 14.1 v and the trip point for the BMS appears to be cell voltage >4v. I guess in the case of 'Drop In' LFP you don't have externally available charge disable output so it's possible that if BMS in battery triggers you will lose DC power. As others have said, it should not happen if charging devices are properly programmed.

I do have a separate start battery that is charged via a Balmar Duo charge from house bank. There is a battery switch that connects either start battery or house bank to starter for emergency start from house bank.

Bill
Right, when I talked with Balmar tech support, even if programmed properly, the 6 minutes in bulk mode could be enough, in rare cases, to trip a BMS in a 'drop in' battery. they suggested a buffer FLA battery in the system to prevent that. My question, is , effectively, how to do that
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Old 21-09-2023, 11:30   #13
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Re: System redesign to drop in LFP

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Originally Posted by phantomracer View Post
Right, when I talked with Balmar tech support, even if programmed properly, the 6 minutes in bulk mode could be enough, in rare cases, to trip a BMS in a 'drop in' battery. they suggested a buffer FLA battery in the system to prevent that.
NOT if you programed the voltage correctly!

All this has been ironed out
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Old 21-09-2023, 11:33   #14
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Re: System redesign to drop in LFP

Quote:
Originally Posted by phantomracer View Post
Right, when I talked with Balmar tech support, even if programmed properly, the 6 minutes in bulk mode could be enough, in rare cases, to trip a BMS in a 'drop in' battery. they suggested a buffer FLA battery in the system to prevent that.
NOT if you programed the voltage correctly!

All this has all been ironed out
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Old 21-09-2023, 11:57   #15
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Re: System redesign to drop in LFP

Quote:
Originally Posted by phantomracer View Post
Right, when I talked with Balmar tech support, even if programmed properly, the 6 minutes in bulk mode could be enough, in rare cases, to trip a BMS in a 'drop in' battery. they suggested a buffer FLA battery in the system to prevent that. My question, is , effectively, how to do that
Don't know. I just wired a lead acid in parallel with the LFP. That was a couple of years ago, still working fine and provides redundancy if the LFP BMS shuts down.

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