The effects of how you ground

[Arbee]

I'm a newbie.

I own a Renogy DCC30S MPPT DC to DC charger. It's suppose to charge house and starter batteries from either a solar panel or an alternator.

Initially testing has found my house battery to not be charged more than 13.08Volts, despite proving out all the connections to be live. There could be many reasons why I see this low voltage, but I did configure the product for the house battery being Lithium, as the house battery is a Renogy 20 amp LiFePO4 with built in heater. Because voltage thresholds on the house battery aren't being met, no way will the product allow any of the solar power to also go into charging the starter battery.

I was thinking that the following mistake on my part might have significant consequences (or not?) and seek your opinion:

The conceptual diagram in the product's manual has all the negative/ground wires of the house and starter batteries, as well as that of the solar panel meeting at the one common ground terminal on the product. In the following video from Renogy though it is recommended that this common point where ground wires meet be the negative terminal of the house battery, and that one cable from the negative terminal of the house battery connect to the ground point on the product.

I will change this tomorrow. But could this be "a," if not the only problem?

Stupid me. Here I'm wondering how Renogy expects me to close the cover to this product with all these 3 negative cables meeting at the ground point on the product. No--clearly only one wire is suppose to attach to this grounding point on the product, and I am suppose to connect the other end of the cable to the negative terminal on the house battery, and have the starter battery and solar panel's grounds meet at this negative terminal on the house battery.

Stupid, stupid, stupid....but what I'd like to know is if my error is possibly relevant? BTW: the negative cable on my starter battery in this system, at its distal end, connects to the negative terminal of the starter battery, as does a factory cable that leads to the vehicle's chassis.

Thank you.

 

[FilterGuy]

Did you ever figure this out?

 

[Arbee]

Well, if the question is, "does where your grounds pair up matter (here)" the answer is it does not.

If the question though is regarding getting the DCC50/30S device to not only charge the house battery but the starter battery as well, I have made progress by purchasing Renogy's BT-2 bluetooth module, which allows customization of not only the battery type the DCC50/30S thinks is the house battery (a feature BTW that is configurable without the BT-2 device) but various voltage thresholds, by using the Renogy BT smartphone app. Setting such custom Voltages is only doable via the BT-2/Renogy BT app combination.

More to point, one of the things that the BT-2/Renogy BT hardware/software combination allows, that can't be done without this pair, is to set a battery type for the house battery called "User." For me, if I wanted this "User" battery type to act no differently than the "Lithium" battery type that's otherwise selectable from the DCC50/30S without the BT-2/Renogy BT combination, and that I otherwise have as my battery, it would still have benefit for me because the DCC50/30S will not attempt to charge a Lithium battery type when the temperature is below freezing.

While this is, of course, a very useful feature to not damage a LiFePO4 battery (short of reducing charge rates at such cold temperatures,) it is actually not needed in my case, and in fact a hindrance to me. I say this because the Relion 20 amp LT LiFePO4 battery that I'm using as my house battery not only already has a BMS that would prevent the charge if this battery were at freezing temperatures, but the battery uses this charge current to initially heat the battery if necessary, before allowing the charge to occur. So I need the DCC50/30S to send power regardless of the temperature, which it will do as long as the battery type is NOT "Lithium."

(There is no configuration capabilities with this product for the starter battery.)

The second functionality the BT-2/Renogy BT app provided for me was to reduce the voltage at which the DCC50/30S starts using solar power to charge BOTH the house and (trickle charge) the starter battery. Solar power always charges the house battery first on this device.

I don't need my LiFePO4 battery fully charged, as reducing such voltage thresholds might do, and it's not only NOT damaging to the battery to avoid fully charging it, as Will (Prowse) has pointed out, controlled running and charging of a LiFePO4 battery around its 50% SOC can be a great way to preserve it. All that this house battery of mine energizes is a silly little 4.5W drawing dash camera.

The only reason this whole project got started is because I already have a roof rack on my vehicle (a Wrangler) to put a solar panel on, and the dash camera was originally connected to the starter battery when the vehicle was parked. On cold nights the starter battery's voltage would drop below the dash camera's configurable cut out voltage--to preserve the starter battery--despite the starter battery being on its own A/C trickle charger.

With this setup I have the advantage of the LiFePO4 battery's inherent greater insensitivity to voltage drops with temperature drops, and the ability to trickle charge the starter battery wherever I go, when it's light out. Additionally, the DCC50/30S product lets me charge both batteries when the engine is cranked, and from both energy sources (engine and sun) if it's light out

Those who run my vehicle, which actually has two starter batteries by factory design (JL 3.6L Wrangler) for the engine start stop system, will comment on how many owners find it necessary to trickle charge the vehicle to keep the engine start stop system working.

(The irony of saving money on gasoline with the engine start stop system at traffic lights, by spending money on the electric to run a shore trickle charger was not lost on me.)