Solar, converter and DC-DC charger they all add up

[nvs4602]

When upgrading to lithium make sure you know the current your batteries can be charged at. Reason being, all your means to charge your batteries are cumulative. So if your DC-DC charger puts ot 40amps and you solar charge controller is putting out 30amps you will be charging at 70amps. And if you plug into shore power or run the generator your converter will add another 50amps so now your charging at 120amps. So you could be over charging your battery. Hopefully your bms will protect the battery and shut off.

I could see the scenario happening pretty easily. So make sure when looking at batteries you know their charge current and plan your system accordingly. I hadn't really thought about it when planning mine but noticed while I was checking everything out after install I was charging at 86amps with both the DC-DC charger and the converter on.

[TitanMike]

What you point out is certainly possible and of serious concern if only a single 100 ah battery in the system.

Max recommended C-rate for charging most LiFePo4 batteries is .5C. That's 50 amp for a 100 ah battery or 100 amp for the more common "two in parallel".

Running a DC-DC charger AND a Converter at the same time is highly unlikely so the proposed scenario may never happen.

If it does the BMS will shut off all charging current until it drops below it's capacity.

One surefire solution if charging capacity in total could exceed .5C is to just add another 100 ah of battery capacity and enjoy

[sdelam]

Good point, thanks for mentioning it.

As an example, Battle Born recommends a charge rate of 50amps per 100 ah battery. I’m running two batteries so my max recommended charge rate is 100amps. 600w of Solar = ~33amps, if I use shore power/generator that adds another ~50 amps for total of ~83 amps. I don’t foresee having the tow vehicle running while using shore power/generator but it only adds another 10-11 amps, so I should be good to go.

[TitanMike]

Originally Posted by sdelam

Good point, thanks for mentioning it.

As an example, Battle Born recommends a charge rate of 50amps per 100 ah battery. I’m running two batteries so my max recommended charge rate is 100amps. 600w of Solar = ~33amps, if I use shore power/generator that adds another ~50 amps for total of ~83 amps. I don’t foresee having the tow vehicle running while using shore power/generator but it only adds another 10-11 amps, so I should be good to go.

Remember that that ~33 amp of solar will also depend on the angle of the Sun so peak charging current won't ever exceed what the BMS allows.

[nvs4602]

There is a lot of people in motorhomes that have solar and DC-DC charger. Then may decide to run the generator for their roof AC. just wanted to make sure they realize what effect that would have on charging.

On the flip side it's also good to know if you want or need to charge your batteries faster. You can use two charging sources together.

[TacomaJoe]

In the OP photo it shows -85.7A, isn't that a discharge? On my BMS, positive current is charging and negative current is discharging.

[nvs4602]

No mine is bass ackwards. It's a quirk of the Daly bms. That a lot of people complain about.

[corn18]

Originally Posted by nvs4602

There is a lot of people in motorhomes that have solar and DC-DC charger. Then may decide to run the generator for their roof AC. just wanted to make sure they realize what effect that would have on charging.

On the flip side it's also good to know if you want or need to charge your batteries faster. You can use two charging sources together.

This is even more true for FLA batteries. LFP will hopefully protect themselves from over charge current. FLA will just boil off and explode.

I have a Victron inverter/charger that can output 120A charging. My solar can add another 70A (I saw that much the other day). And if I am hooking up the truck while still connected to shore power, that will add another 20A. So 210A total. My LFPs will reject all of that if they don't need it. Push that many amps into an FLA battery and you better hide somewhere.

[Half Ton Heavy]

Originally Posted by nvs4602

No mine is bass ackwards. It's a quirk of the Daly bms. That a lot of people complain about.

I’d be happy with BT on my 200 amp Daly BMS. As it is, I depend on my BMV 712 instead. As time goes on, I hear a lot of folks not happy with Daly BMS’s, which is a little concerning.

[nvs4602]

Originally Posted by Half Ton Heavy

I’d be happy with BT on my 200 amp Daly BMS. As it is, I depend on my BMV 712 instead. As time goes on, I hear a lot of folks not happy with Daly BMS’s, which is a little concerning.

I like Daly so far. It has been doing what it's supposed to do. The Bluetooth is a plus and I probably won't order another bms without it. I also installed a AliExpress shunt battery monitor. And they both read very close to each other. I think it's the refresh rate of the Bluetooth that keeps them different.