Can I simultaneously charge 2 separate batteries with one solar blanket?

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Clive Atkinson asked Oct 25, '20

Can I simultaneously charge 2 separate batteries with one solar blanket?

I have a 200W solar blanket charging a 120AH AGM battery in my caravan using a Victron SmartSolar MPPT 75/15.

I also have a 100AH LifePO4 Battery in my vehicle to run the portable fridge. I can charge this from the same solar panel using another Victron SmartSolar MPPT 75/15. But if the caravan battery is charging, I have to disconnect the solar blanket lead and connect it to the charge controller in the vehicle to charge the LifePO4 battery.

Is it possible to split the cable from the solar blanket to then run cables to both of my Victron charge controllers thereby charging both batteries simultaneously?

So, in summary, I have 2 charge controllers, 2 batteries and one solar blanket and I want to charge them both at the same time.

Forgive my ignorance of 12V stuff!

battery charging MPPT SmartSolar

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Answer 1 · 2020-10-25T16:31:49Z

Matthias Lange - DE answered · Oct 25, 2020 at 04:31 PM

No that will not work.
Both controllers try to find the MPP and "fight" against each other.

https://community.victronenergy.com/questions/41148/two-mppt-on-one-solar-string-possible.html

https://community.victronenergy.com/questions/45553/can-or-i-cant-to-connect-two-mppt-in-parallel-mode.html

https://community.victronenergy.com/questions/59817/single-pv-with-2-x-mppts.html

https://community.victronenergy.com/questions/49236/can-i-split-a-series-feed-into-2-x-mppts.html

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Answer 2 · 2020-10-25T19:12:11Z

bathnm answered · Oct 25, 2020 at 07:12 PM

A solar panel can only connect to one Solar Controller, so no it will not ork. However there are options.

I would connect the Solar to the Lithium bank and then use something like a Cyrix-Li-Ct or maybe even a DC-DC Charger such as the Orion TR Smart to join the two batteries when charging is required. The advantage of a Cyrix-Li-Ct is that it could also join the AGM to the Lithium when you have the engine running to also charge the Lithium from. the alternator.

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Answer 3 · 2020-10-26T09:12:17Z

Clive Atkinson answered · Oct 26, 2020 at 09:12 AM

Thanks for the answers. I'll go and get another solar panel.

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Answer 4 · 2020-12-05T15:38:41Z

Trina answered · Dec 05, 2020 at 03:38 PM

Sounds solved and I like the OP solution.

I wanted to point out to anyone coming to this thread later that you really need to correctly size your lifepo4 charger setup

While LifePo4 can handle a lot of current, an average van charger will be at least 70 amps and that really is pushing it for a 100ah lifepo4 once the AGM Is done charging (probably within a few minutes at most). 70a is a bit strong for a 100ah lifepo4 if you want it to last 10 years.

The other option to a 2nd solar panel is to run the agm off the lifepo4. If you wired the lifepo4 between the mppt and agm and set the MPPT for the agm the lifepo4 BMS would take it in (or out) of the loop as needed -such as when it was done charging, or bringing.it.back "in" to assist or charge the agm as it brought the slower charging agm up to state. In effect one would be cycling off the lifepo4. This of course would not be as effective being that the mppt would not be giving max amps possibly sometimes when.the lifepo4 could handle it. But of course that would be rare (and theoretical on a small setup). You'd probably also see a bit of strange behaviours out of the MPPT but if you set it for the agm it should be fine.

I would separate them for non solar use of course.and just reconnect for recharging.

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