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Old 14-04-2020, 14:28   #1
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Separate LiFePO4 batteries from Alternator Charging

My vessel uses a bank of LiFePO4 batteries for the house, and separate AGM batteries for each engine battery ( 2 SGM for our two engine catamaran). The alternators for each engine are each connected to a battery isolators (Cristec RCE/100-1E-2IG - one input, two outputs). One output goes to the LIFePO4 battery bank, the other to the respective (port, starboard) engine battery. I assume the isolators pushes current to the output port having the lowest voltage potential with respect to the ground.

I have not yet used the engines to charge up the LiFePO4 house bank. I have plenty of solar.

As the average voltage of the LiFePO4 is around 12.5v, I suspect the isolators never route current to the LiFePO4. When the solar panels are working the voltage at the batteries is around 14.6V.

First, am I damaging any of my batteries with the alternator charging two different types of batteries? Damaging either the LiFePO4 or AGMs?

Second, should I simply disconnect the LiFePO4 from the isolators and let the alternator simply charge the engine batteries?

Thanks!
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Old 14-04-2020, 18:24   #2
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Re: Separate LiFePO4 batteries from Alternator Charging

Look into dc-dc chargers. Your alternator will charge the start and the dc-dc will pull power for the LiFePO4.

I use the Victron version. Bluetooth is useful and the manual switch is even better. I don’t keep it on, only will use it when needed. I have some solar, more is better. Fun in the sun watching the solar at full tilt, combined with alternator charging.
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Old 14-04-2020, 19:36   #3
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Re: Separate LiFePO4 batteries from Alternator Charging

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Originally Posted by geekoman View Post
My vessel uses a bank of LiFePO4 batteries for the house, and separate AGM batteries for each engine battery ( 2 SGM for our two engine catamaran). The alternators for each engine are each connected to a battery isolators (Cristec RCE/100-1E-2IG - one input, two outputs). One output goes to the LIFePO4 battery bank, the other to the respective (port, starboard) engine battery. I assume the isolators pushes current to the output port having the lowest voltage potential with respect to the ground.

I have not yet used the engines to charge up the LiFePO4 house bank. I have plenty of solar.

As the average voltage of the LiFePO4 is around 12.5v, I suspect the isolators never route current to the LiFePO4. When the solar panels are working the voltage at the batteries is around 14.6V.

First, am I damaging any of my batteries with the alternator charging two different types of batteries? Damaging either the LiFePO4 or AGMs?

Second, should I simply disconnect the LiFePO4 from the isolators and let the alternator simply charge the engine batteries?

Thanks!
It's unclear what type of regulator you are using. If it is the built in on the alternator, I would suggest you change that out asap. With a decent 3 stage regulator, the optimum bulk charge current for the AGMs from the alternator will be fine for the LIPO, so you could use the alternator for both. How you manage that charge cycle is a whole other conversation and there are lots of discussions on proper charging routine for lithium on this site.

I'd also note that if your LIPO batteries are averaging 12.5 vdc, they are, on average severely depleted. I only see that voltage after taking out 90% of capacity, so I wonder if you are chronically undercharging them, which ain't good.
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Old 14-04-2020, 20:15   #4
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Re: Separate LiFePO4 batteries from Alternator Charging

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Originally Posted by Delfin View Post
I'd also note that if your LIPO batteries are averaging 12.5 vdc, they are, on average severely depleted. I only see that voltage after taking out 90% of capacity, so I wonder if you are chronically undercharging them, which ain't good.
This is the main thing I observed. My LIPO bank is usually around 13.3v. Lowest I've seen it is 12.95v I believe. I charge it to 14.6v, as per manufacturer recommendation.

Make sure you're measuring battery voltage with a shunt as close to the battery as possible.
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Old 15-04-2020, 00:06   #5
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Re: Separate LiFePO4 batteries from Alternator Charging

Quote:
Originally Posted by geekoman View Post
My vessel uses a bank of LiFePO4 batteries for the house, and separate AGM batteries for each engine battery ( 2 SGM for our two engine catamaran). The alternators for each engine are each connected to a battery isolators (Cristec RCE/100-1E-2IG - one input, two outputs). One output goes to the LIFePO4 battery bank, the other to the respective (port, starboard) engine battery. I assume the isolators pushes current to the output port having the lowest voltage potential with respect to the ground.

I have not yet used the engines to charge up the LiFePO4 house bank. I have plenty of solar.

As the average voltage of the LiFePO4 is around 12.5v, I suspect the isolators never route current to the LiFePO4. When the solar panels are working the voltage at the batteries is around 14.6V.

First, am I damaging any of my batteries with the alternator charging two different types of batteries? Damaging either the LiFePO4 or AGMs?

Second, should I simply disconnect the LiFePO4 from the isolators and let the alternator simply charge the engine batteries?

Thanks!
That is what we do, we connect or disconnect the house from the alternators based on SOC by a BMV 712 monitor using its auxilary relay contacts.
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Old 15-04-2020, 04:31   #6
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Re: Separate LiFePO4 batteries from Alternator Charging

I concur with the voltage numbers you all are quoting. I read my 12.5 off the battery’s data sheet (ReLion RB300) and at a discharge rate of 2C voltage drops down to 12.5. A more typical voltage is 13.25. Mine are now reading 13.32v at 84%, solar panels turned off so not to read charging voltage.

I also have the BVM 712 and will look at its capability to disconnect the LiFePO4 from the alternator. Interesting idea!

Thank you!
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