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Old 27-03-2020, 05:10   #1
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Charging dual banks - one AGM and one lithium.

I'm looking for advice on how to set up a system to charge two seperate banks - one consisting of 4 8D AGMs with 245Ah capacity each, the other a Relion RB300 integrated lithium ion battery. I'm looking at adding the RB300 and connecting a few specific loads to it (fridge, freezer, and Electroscan MSD), leaving all other loads on the existing AGM bank.

My charging sources are as follows:
- Xantrex SW3012 inverter/charger (when on shore or generator power)
- 100A engine alternator with Balmar ARS-5 external regulator
- 2x 350watt solar panels, each connected to individual Victron 100/30 charge controllers.

I'm imagining a system that prioritizes the RB300, as it will charge much faster than the AGM, then once the lithium battery is full will send the power to charge the AGMs. But perhaps there's a better, simpler way...

Regards,
David
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Old 27-03-2020, 06:57   #2
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Re: Charging dual banks - one AGM and one lithium.

The Lithium versions of the Yandina Combiner or Trollbridge allow mixing of lead-acid and Lithium batteries without the problem of the higher voltage Lithium batteries discharging into the lead-acid batteries once charging ceases. They will charge from sources rated up to 100 amps and deliver all available current to the destination battery while protecting the alternator from overload.
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Old 27-03-2020, 20:36   #3
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Re: Charging dual banks - one AGM and one lithium.

most of those intergrated li batteries have max charging rates not that high. so I would check that limit first.

personally I would just get a 12v dc to dc charger and charge the lith bank from the agm, and leave all other wiring in place charging the agm first.

I've installed a couple of the mastervolt mac 12/12 -50a latly and like those. you also need the mastervolt usb gateway to program though.
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Old 28-03-2020, 05:42   #4
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Re: Charging dual banks - one AGM and one lithium.

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Originally Posted by smac999 View Post
most of those intergrated li batteries have max charging rates not that high. so I would check that limit first.

personally I would just get a 12v dc to dc charger and charge the lith bank from the agm, and leave all other wiring in place charging the agm first.

I've installed a couple of the mastervolt mac 12/12 -50a latly and like those. you also need the mastervolt usb gateway to program though.
I see this technique dc/dc often

Seems to be the best solution for dissimilar banks or awkward battery location
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Old 28-03-2020, 09:45   #5
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Re: Charging dual banks - one AGM and one lithium.

I'm in the same position having installed 200 amp hours of lithium to run my fridge. I eventually decided that the lithiums were to damned expensive to take a risk with and bought a second solar regulator.

I am also building a gas engine powered battery charger and am wondering what is likely to happen when the BMS opens the charge relay on the lithium to drop it off charge suddenly whilst the alternator is still running.
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Old 28-03-2020, 09:59   #6
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Re: Charging dual banks - one AGM and one lithium.

The alternator might blow up. The bms will only open if there is a problem though. Like battery temp or high voltage
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Old 28-03-2020, 10:34   #7
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Re: Charging dual banks - one AGM and one lithium.

Your gas generator should be fine, they are supplied with on/off switches that do the same thing and they are designed to survive that.
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Old 28-03-2020, 11:04   #8
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Re: Charging dual banks - one AGM and one lithium.

Quote:
Originally Posted by Davidhoy View Post
I'm looking for advice on how to set up a system to charge two seperate banks - one consisting of 4 8D AGMs with 245Ah capacity each, the other a Relion RB300 integrated lithium ion battery. I'm looking at adding the RB300 and connecting a few specific loads to it (fridge, freezer, and Electroscan MSD), leaving all other loads on the existing AGM bank.

My charging sources are as follows:
- Xantrex SW3012 inverter/charger (when on shore or generator power)
- 100A engine alternator with Balmar ARS-5 external regulator
- 2x 350watt solar panels, each connected to individual Victron 100/30 charge controllers.

I'm imagining a system that prioritizes the RB300, as it will charge much faster than the AGM, then once the lithium battery is full will send the power to charge the AGMs. But perhaps there's a better, simpler way...

Regards,
David
I will leave your specific electrical question to those more qualified only to say that I don't like mixing battery chemistries. S@#$ happens and at the worst possible time.

I would worry about the sustainability of your batteries even with 2x350W solar panels due to your electrical draw (like to see how you mounted those). Your alternator is at least half the size it should be for charging the 4x8D AGMs. On my last Pacific voyage we were frequently days without full sunshine (something one doesn't expect in the Pacific) but my electrical use was very reasonable and I never had to start the diesel with my 4x140W panels and 2 8D Gels. A genset just wastes fuel you may need later.

I recommend you develop an Offshore Energy Budget and do some "what-ifs" to see how viable your plan is. There is an Excel template on the Pacific Cup website (Sample Energy Budget) that was developed for the race participants and you can modify it to suit your boat including your expected solar panel energy production; it can even calculate your diesel consumption for charging. I included EVERY single electrical item on the boat and my solar panels...it was very enlightening.

Good luck.

~ ~ _/) ~ ~ MJH
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Old 24-04-2020, 02:26   #9
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Re: Charging dual banks - one AGM and one lithium.

I'm no expert but currently have a post running which looks at replacing my battery bank.
One of the contributors described his setup.
He has directed All of the different charging systems to the house bank.
The house bank then charges the Start battery (or 2nd bank) through a charge controller.
Pretty simple system.
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