Renogy 50amp DC to DC Charger with MPPT issues...

[jmden]

First one purchased last November ('22). Worked great for several months on several trips, often getting almost 50 amps out of the alternator. Usually would take a 4-5 day trip every other month.

Then in May all of a sudden I was only getting mid 30s on amps. And it went down from there on the next trip to about 18 amps.

Tow vehicle (TV) is a 2014 Ford Expedition with a 175 amp 'dumb' alternator. I have a 40' run from the TV starter battery to the DC to DC charger in the trailer using 4 gauge cable with an Anderson connector at the bumper.

After many hours with Renogy customer service (ahem...) their 2nd level US based customer service sent me a new unit. Right of the bat for a few minutes it was at 45 amps, then as driving progressed that day, we went to about 35 amp and it stayed there the rest of the trip.

I have done a bunch of testing of the battery and alternator, at one point showing the alternator putting out 135 amps on the cable that runs to the starter battery, with just about everything turned on that I could to make the alternator work hard. The battery is a couple of years old. Battery and alternator tests with my code reader show both as good. Auto parts testing for both shows the same. I can't find anything wrong so far except the amp dropping from the steady 45 amps or so that we had for several trip after installing the first charger.

Any educated thoughts would be helpful. If this is in the wrong place, please excuse me and move it. Thanks!

 

[Tomthumb62]

Sounds normal. Is your battery getting close to full charge? It won’t spit out 40-50A right up until 100% SOC. It will derate as it gets fuller.

 

[mikefitz]

One issue, assuming your battery is in a state to accept charge, is that most DC to DC chargers ramp down the power output if they exceed thermal limits.
Since the long cable run is dropping over 1 volt, the conversion process has to work harder , thus more heat.

Have you investigated, the current into the unit, the voltage at the input terminals and the temperature reached by the unit?

Mike

 

[Tomthumb62]

First one purchased last November ('22). Worked great for several months on several trips

Then in May all of a sudden I was only getting mid 30s on amps.

most DC to DC chargers ramp down the power output if they exceed thermal limits.
Since the long cable run is dropping over 1 volt, the conversion process has to work harder , thus more heat.

I think this is your answer. Assuming you are in the Northern Hemisphere and perhaps in a climate that gets somewhat "real" 4-seasons, such as cold winters, then when you first got your rig, it was cold, thus the charger was able to throw off the extra heat.

Your fix would not be cheap...it would require upgrading your 40' cable run to much thicker cable. If you have 2AWG there now, you might consider 2/0. If you have 2/0, then consider 3/0 or even 4/0.

Ok - I ran the maths. At 50A, 80' total length (40' each leg) for a 3% voltage drop, you want 2/0 AWG.

Without searching real hard, this is the best quality+price I've come up with for 2/0 welding cable, $399 for a 100-foot roll. It's all black, so you'd want to get some red heat-shrink to mark the ends and perhaps every few feet so you know which is which.

https://www.amazon.com/TEMCo-WC0009-100-Welding-Battery-Copper/dp/B00LIB3YF8?th=1

 

[740GLE]

Even at 15A are you not driving long enough to fully charge the battery?

Running 2/0 is costly.

I would check if you are actually seeing a voltage drop before upgrading the cabling

 

[Tomthumb62]

Even at 15A are you not driving long enough to fully charge the battery?

Running 2/0 is costly.

I would check if you are actually seeing a voltage drop before upgrading the cabling

Not sure where @mikefitz saw a 1V drop, but that would be a big problem.

 

[740GLE]

Also we have no idea what battery is in the trailer,

We got tons of info on everything else except the most important part, what is being charged.

 

[mikefitz]

Not sure where @mikefitz saw a 1V drop

40 foot run fron starter battery, 4AWG, 50 amps current

 

[pollenface]

Sounds like normal charging behavior without any extra info (loads, battery voltage, etc)

 

[740GLE]

40 foot run fron starter battery, 4AWG, 50 amps current

How do we know the batteries need 50A?

 

[mikefitz]

The OP states 45 to 50 amps initally, that progressively dropped during the drive.
The charger is nominally rated at 50 amps output, there will conversion losses and thus heat. The higher the differential between input and output volts, the higher the conversion loss and the higher the input current.
Most makes of DC to DC battery to battery chargers have thermal protection and those with passive cooling seem more prone to ramping down the power output when hot. This may be the issue.

 

[jmden]

Trailer (house battery) is a 206 Ah SOK LiFePo4. The DC/DC charger(s) aren't putting out anywhere near what they should even when the house battery is well below 13V and SOC is way under 50%.

I also have numerous Renogy app screenshots showing house battery volts at 13.3 and starter battery volts at 13.1. Not sure that's voltage drop. I'd need to check voltage at the starter battery and voltage at the terminal where the positive cable goes into the DC/DC charger for that, right? Not sure I've done that. Will report back.

The battery sux down over 50 amps from the converter when on shore power until it is at 100% SOC.

 

[jmden]

I think this is your answer. Assuming you are in the Northern Hemisphere and perhaps in a climate that gets somewhat "real" 4-seasons, such as cold winters, then when you first got your rig, it was cold, thus the charger was able to throw off the extra heat.

Your fix would not be cheap...it would require upgrading your 40' cable run to much thicker cable. If you have 2AWG there now, you might consider 2/0. If you have 2/0, then consider 3/0 or even 4/0.

Ok - I ran the maths. At 50A, 80' total length (40' each leg) for a 3% voltage drop, you want 2/0 AWG.

Without searching real hard, this is the best quality+price I've come up with for 2/0 welding cable, $399 for a 100-foot roll. It's all black, so you'd want to get some red heat-shrink to mark the ends and perhaps every few feet so you know which is which.

https://www.amazon.com/TEMCo-WC0009-100-Welding-Battery-Copper/dp/B00LIB3YF8?th=1

In northern Washington State so, the temperature thing has been in the back of my mind in regards to the cable size and what the DC/DC charger might do...

 

[jmden]

One issue, assuming your battery is in a state to accept charge, is that most DC to DC chargers ramp down the power output if they exceed thermal limits.
Since the long cable run is dropping over 1 volt, the conversion process has to work harder , thus more heat.

Have you investigated, the current into the unit, the voltage at the input terminals and the temperature reached by the unit?

Mike

I didn't have and issue with this until a trip in May. The trip before was in March. The battery, inverter and DC/DC charger are under the seat cushions of the dinette, so I've been removing the cushions and plywood under it when traveling since in order to release the heat. Two passive roof vents in trailer are open when traveling as well.

The inverter is intermittently pulling about 25 amps off the battery to run the refrigerator on AC while traveling so we aren't using propane to do that. For the first few months traveling with the DC/DC charger, we'd typically get 45+ amps off of it and so it was running the fridge leaving an extra 20 amps or so to charge the battery. Not so much now.

I don't know the temp actually reached by the unit.

 

[jmden]

Any other thoughts...?

 

[740GLE]

I’d run the propane fridge and save the battery for other loads, those fridges hardly suck down the propane. But that’s just me.

Are there setting in the Renolgy for charging voltages?

Also have you verified the battery terminal voltages with a meter vs the app?

If the app thinks it’s 13.5v but the battery is actually closer to 13.1v that’s the voltage drop of concern.

 

[philammon]

I've heard others say this unit can get hot. Try measuring at the heat sink with a temperature meter on MAX/HOLD. If the heat sink is getting close to 70C then I agree with the possibility of thermal limiting. In that case, a couple of small fans with integral thermal sensing blowing across the heat sink would be a big help. The Renogy manual says the charger can be mounted vertically or horizontally, but I believe a vertical mounting, with the heat sink spaced a few cm from the mounting surface would be best. For fans, you could look at these: https://www.amazon.com/ARCTIC-Tempe...iguration/dp/B0037AUS4S/keywords=Arctic+F8+TC
Even in an enclosed space that could significantly improve the heat extraction from the charger. On an unrelated note, how do you have the trailer's converter and DC loads connected? I am considering a similar setup for our trailer/TV.