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Connecting Solar - Altenator - shore power charger to one set of batteries

ActionJackson

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Oct 20, 2020
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I am concerned about setting up three different battery chargers (Solar charger, Renogy 40amp dc to dc, and 110 to DC off-brand. All three monitor the batteries for overcharging but they are not connected and there are times where all three could be charging at the same time. Yes, I am a noob but it seems like the batteries could be overcharged in this setup. Am I overthinking this?
 
Yes. You are overthinking this.

Battery charging works on a constant-current to a voltage phase followed by a constant voltage phase. In the constant current phase, all chargers will push max current until they sense the absorption voltage, then they will start tapering current to hold the voltage. Each charger will respond according to battery voltage. Towards the end of the charge, it's common for the highest current charger to be the only one operating in the constant voltage phase.

Other concerns:

If FLA or AGM batteries, the max charge current should be 10-15% of the capacity (100Ah should be charged at 10A). AGM can go to 20% typically. It's important that the total sources not exceed this value in the constant current phase. Once the batteries are in the second phase of charging, it doesn't matter, because voltage is the limiting factor.

If LFP, connecting one directly to an alternator will stress the alternator because they can take whatever the alternator can deliver for an extended period of time. Alternators are not made to operate at or near 100% for extended period. There are DC-DC converters that take alternator output and supply a reduced current for charging. There are also devices that only permit charging about 50% of the time (cycles on and off about every 15 minutes).
 
So... we have the Renogy DC to DC charger for the alternator so that will limit the charge from the alternator, I believe. But how do we keep each of the three chargers from supplying too much current? We will likely be using (4) Everstart flooded lead-acid battery to start due to price and Wal-Mart 2 year replacement warranty. Is there a charge controller that can accept all input or how do we make sure the Renogy Wanderer solar charger, Renogy DC to DC charger, and the 110v to 12v charger don't overcharge?
 
If you have a 5 gallon bucket of water and a 1 inch hole, you can dump the entire bucket of water onto the hole, but the hole will only take so much water.

The chargers are the bucket of water.

The battery is the hole.

When current is supplied is causes voltage to rise. More current, more voltage. Once voltage gets to the programmed absorption voltage, all chargers will see this and then send only enough current to maintain that voltage. In the analogy, when the battery can't take more, the "hole" gets smaller.

Consider that each of the 120VAC outlets in a house can deliver as much as 2000W of power, or 15-20A of current. Why aren't you worried about plugging a 13W LED using only 0.1A into the power socket when the socket can deliver 100X that current?

The battery "talks" back to the chargers via its voltage, and the chargers respond accordingly. It's your responsibility to ensure all charge sources are programmed for your battery.

Unfortunately, Everstarts are pretty much junk. Count on them not lasting the two years unless you are VERY gentle to them with only slight discharges. They aren't really "deep cycle" batteries. They're more typical of starter batteries and have a poor cycle life. If you got the ones rated for "122Ah" note that is only for a 1A discharge. They are closer to 60-80Ah when you look at a 20 hour (standard) discharge rate.

You need to check their electrolyte levels frequently.

While it's not directly applicable to your batteries, the following two resources are a good education on flooded acid batteries, their opration and their maintenance:


 
AJ, on my RV trailer I watched the solar charge controller monitor as my AC-DC converter came online. The solar charge controller dropped down to zero amps when the converter started its charge. The solar charge controller will do the same thing when I connect my trailer to the truck's alternator.

As long as your components aren't stupid, it works out. My components are all smart enough to figure it out. They are specifically designed to work in an environment like mine. If you use some off-the-wall component that was never designed for this type of environment then perhaps it won't play well with others.
 
One more add-on, we're using a IOTA Engineering (DLS30 30 Amp Power Converter/Battery Charger). We changed and went with (2) Lithium LifePo 100ah batteries. The charger does NOT have a setting for Lithium batteries, do we need to upgrade the charger, add the IOTA Engineering IQ4 Smart Charger, or do you think we're good to go as is?
 
The DLS30 puts out a constant 13.4V, which is fine safety-wise, but you'll never get fully charged. They do make a IQ4 specifically for LFP:


Unfortunately, it doesn't indicate the voltages, and it's only 2 stage. There is also a 3 stage gel IQ4 module that I'd consider since gel voltages typically play well with LFP provided their float isn't too high.
 
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