Renogy DCC30S and LiFePO4 battery charge


Solar Enthusiast
I've got the above Renogy MPPT DC/DC charger, a 100W solar panel and a 20 amp LiFePO4 Relion house battery with the LT (low temperature) feature: where current is used to heat the battery, need be, first, before it is applied to charge the battery.

Relion says this heating should slow down charging by maybe an hour or so over times when such heating is not needed.

Normally you'd think a 100W panel charging a 20 amp LiFePO4 battery would be (correct me if I'm wrong) child's play for the solar panel. But I rarely get voltages in this Relion battery beyond 13.4V.

Would anyone care to conjecture on why I'm not achieving higher voltages on the Relion battery? Is it my user voltage settings, or the current going to initially heat the battery, or the cold temperatures causing the battery's BMS to reduce the current allowed into the battery? Currently nothing is drawing power from the Relion battery but the DCC30S itself. Are these voltages normal. Should I wait for temperatures in the 40's + Farenheit before drawing conclusions.

I was really hoping that this 100W panel would quickly charge the LiFePO4 battery so it could get to the business thereafter of trickle charging the starter battery.

I have the battery type of the house battery set to "User" type via the Renogy BT-2 WiFi product, and the Renogy BT or DC Home app on my smart phone. My voltage settings are similar to that of the Lithium type, just tweaked somewhat based on posts here.

I'd consider abandoning use of the DCC30S but know of no DC MPPT charging competitor that trickle charges the starter battery. Perhaps I need a dual MPPT charger and DC/DC charger.

Is there such a thing as DC/DC chargers that not only let the starter battery charge the house battery when the alternator is running, but the house battery (trickle) charge the starter battery when the house battery has the current to do so?



A 100 watt panel in the middle of winter isn't going to produce a lot of power, especially if it isn't aimed toward the sun. That may be part of your problem. If it takes an hour for the battery to come up to temperature, you've lost that much charging time.

My battery warming system is active 24 hours a day. When the sun comes up, the LiFePO4 batteries are ready to take a charge. But I have 560 Ah of battery capacity. I can run my warmers for days with no solar input. I don't think you have that option with a battery with only 20 Ah.


New Member
Some more details might help diagnose your problem.

When you say 20 Amp you mean 20 Amp Hour right?

Where are you located?

What sort of temps are you dealing with?

Can we assume that your panel is getting full sun and not shaded by trees etc?

Have you measured the charge current?


Solar Enthusiast
@HRTKD thank you for your perspective and knowledge. Clearly, based on your thoughts, my thinking that a 100W solar panel on the roof of my Jeep Wrangler, in no way angled towards the sun, was an overengineered solution, is flawed, I imagine particularly in winter where sunlight in my locale is not only less, but some of those daylight hours are spent converting charging current first into heat to warm the battery in need to see how this works in warmer months of longer days.

It sounds like your battery warming system @HRTKD is independent of the battery. Mine is not. @Rayinaz its a Relion 20 amp hour LT battery that will only turn on the warmer when it detects current from a charging source, rather than tap the battery's supply itself for that current needed to effect the warming as I speculate @HRTKD's setup does.

I'm in the Northeast. And while my panel has no obstacle blocking it, it sits on the top of my vehicle's roof, not angled toward the sun, and certainly, sunny days are by no means the norm this time of year as sure as short days are.

I have not measured the charge current beyond that shown by either the Renogy BT or Renogy DC Home smart phone apps that Renogy supplies for use if you also purchase (as I have) their BT-2 serial port to WiFi product. Current caries, as does the power, as I assume the DCC30S' MPPT charge controller tries to maximize power by regulating voltage and amps--if that's what you're asking.


New Member
Arbee: I've noticed this a bit late and I don't know whether I'm missing something here, but 13.4V is the absolute maximum voltage you can get from a 12V LifePO battery (4 cells) once it has charged fully and charging has stopped. You will only see a higher voltage while it is connected to a charging source, ie the voltage will be from the charger and not the battery, and then the voltage could be 14.4 or more - but only until the charge controller switches off.

Under discharge conditions the voltage will then fall quite rapidly from the initial 13.4 to about 13.0 where it level off till the battery is almost completely discharged. It might be worth checking the open circuit voltage of your panel in full sun - it should be about 20V - and the charging profile of the Renogy - I would try the default lithium settings. It shouldn't take long to charge a 20Ah battery, that's pretty small for a "house" bank - even here in the generally dull weather of the UK you can get about 5A of charging current from a 100W panel on a good day so your battery would be fully charged in about 4 hours (at least once the warming has stopped).

You also haven't mentioned what sort of loads you are putting on the battery - if you have any significant load connected to a 20Ah (240Wh) battery it will discharge pretty quickly, eg a modern 12v TV could easily draw a continuous 4A and a small fridge an average of 2A ie about 600Wh per day.