How to set up Two Battery Chargers on One Battery?

[Ang429]

So I will be using these Power Queen MPPT/DC to DC Chargers to Charge my Lead acid starter battery. One will take Power from a 35W solar panel and put it into the battery during the day, And the other will take 12V From a LFP battery (charged by a 200W Solar panel During the Day) And put it into the Lead Acid Starter battery at night. My problem is how can I stop the one hooked up to the LFP From charging during the day and wasting Power? And Will both of these be able to handle when the Battery jumps to 14V From the alternator, And then stop charging since it will think that the Lead acid is full?

https://www.amazon.com/Board-Charger-Lithium-Battery-Alternator/dp/B0C5DFK5W7/ref=sr_1_3?crid=1SIFZNJM0EHQZ&keywords=Power+queen+dc+to+dc&qid=1700289787&sprefix=power+queen+dc+to+dc%2Caps%2C79&sr=8-3&ufe=app_do%3Aamzn1.fos.18630bbb-fcbb-42f8-9767-857e17e03685

Another Alternative to this would be to just have one Charger, But then I would need to Connect the two solar panels That I will have. One is a Lensun 35W And one is an Ecoflow at 100W. The Lensun is 17V, I'm having a hard time finding the Voltage for the Ecoflow (haven't bought it yet). It says 17.1V 5.9A which is 100W, But then the description says 12V 45A which is obviously wrong, so I have to assume that its 17V, and id be able to check once I get it. But I'm not sure whats the best way to connect them? I'm reading that parallel would work but means if one has shade then they both barely work, or something about the 100W one being limited because the 35W is so much less?

 

[mikefitz]

these Power Queen MPPT/DC to DC Chargers to Charge my Lead acid starter battery.

This type of DC to DC charger, with built in solar charger, is designed to function with the DC input from a vehicle lead acid starter battery. The activation is caused by the increase in starter battery volts as the alternator charges. The Power Queen design , in my view, with flying leads and plugs/sockets for cable conections is poor engineering . Two chargers, configured as you suggest, is unlikely to work well.
Use a single unit, perhaps consider DC to DC/MPPT chargers from other manufactures, between starter and lithium house battery with your 100 watt panel. If you wish to use the 35 watt panel try in parallel with the 100 watt as an experiment.

An alternative model of DC to DC /MPPT will allow solar to charge the starter battery once the lithium is full, the Renogy DCC 30 or 50, so you don't need any further equipment to ensure the vehicle battery is maintained

DCC30S 12V 30A Dual Input DC-DC On-Board Battery Charger with MPPT

Designed to give you options, the Renogy 30A Dual-Input DC-to-DC MPPT On-Board Battery Charger can charge a service battery in two different ways. The multi-stage charger can utilize connected solar panels or an alternator linked to a starting battery. While your vehicle's alternator prioritizes...

www.renogy.com

It's not clear if the Power Queen charger offers this facility.

Mike

 

[AmpD]

2:00 minute mark... If it is all the same voltages then it should be ok to hook up in parallel. In series the shading will affect both panels if shaded. Parallel shading only affects the panel that is shaded.

I watched Will's review recently on the above Renogy DC-DC MPPT. Mike linked you. It sounds promising.

I'm not entirely certain of how charging both batteries when the sun is up wastes power. I think it depends on the LiFePo4 battery but most of them I've seen specifically say don't use as a starting battery.

Is there a reason why hooking up solar to the LiFePo4 and letting it DC-DC charge the lead acid won't work for you? I'm new too but from what I've read this will isolate your starter battery from the system and ensure it maintains a full charge if that is your goal here.