DC to DC charger

Camper_Jeff_&_Kelli wrote:
I'm out in the TC again today idling the engine. Today I shut off all DC loads except 1 LED dinette table light. Inverter and all else is off excepting for dc electronic controls in fridge and water heater. Idling away, my input voltage is 13.6 and the output charge voltage is 13.7. The unit is hot again. It took half an hour to get to the too hot to touch point. Just guessing, 150 to 160 degrees. The unit has a large heat sink on it. Not smelling electronics. If I were to drive the truck and bring up the speed of the alternator and the output voltage, it may raise the charge voltage lowering the current and possibly the temperature. I have not felt the alternator to see what it's temp is/feels like. I'll run out and do a feel temp test on the alternator, and bring the engine up to 2K RPM for a couple minutes to see if that changes voltage readings to the DC DC input and outputs, hang on...
OK, the alternator is warm on the front just after the big radiator cooling fan, and hot a couple inches back to the rear of the alternator. The truck voltage goes from 13.6 at idle to 13.8 when revved to 2K RPM and current goes up just a little varying from 13.2 to 13.8 according to the BMS. The Victron dc dc charger only reports input and output voltage. I need to look at each battery's BMS for its report which differs and includes current. So, Engine RPM makes a small difference on my setup, I don't know if it's enough to change the time to charge or heat profile. I will have to take a drive to do that. My alternator is 160 amps so it should be able to handle the truck load and the dc to dc. It took an hour at idle to bring both batteries up to 90 and 91 percent charge. My latest weather forecast shows clouds and snow the next 6 days so I'll have to do some driving in the TC to keep the system charged. About an hour a day but tomorrow, I think I'll do some extra running around and bring the batteries back up to about 100%, then watch it slowly go down from there, with all the DC stuff that isn't necessary shut off to make things last longer.
About 5 weeks till I get the new Victron 3000 and get shore power again. Even though I installed 675 watts of solar on the roof, it just isn't enough for winter up here in the Seattle area.

Is there any particular reason you didn't mention any specific current readings? Voltage readings alone only tell us a fraction of what's going on with our dc to dc charger. Voltage is akin to water pressure. Current is similar to gauging how many gallons of water are flowing per min. One can have tons of water pressure (or voltage), but have very little to no water (or current) flowing.

To determine how efficiently our dc to dc charger is operating, we take current readings (with max rated charge current at the charger's output terminal) at the power source (i.e., TV alternator/battery terminals) and battery terminals of the battery being charged by the dc to dc charger. These two current readings determine the overall efficiency of our entire dc to dc charger installation. If the efficiency is less than desired, we'll also take voltage readings, along with additional voltage/current readings at the input and output terminals of the dc to dc charger to help locate the source of the efficiency (voltage) drop.

I can't vouch for Victron dc to dc chargers, but Renogy dc to dc chargers can achieve almost 90% efficiency IF large/short enough cables are used on the input and output (and alternator voltage is high enough relative to charge voltage). For what it's worth, our 40a Renogy dc to dc charger is roughly 90% efficient. It uses approx. 44a of alternator current to produce 40a of charge current at the battery terminals.