dc to DC Renogy charger

[pianotuna]

Hi all,

I finally have the dc to DC 20 amp Renogy installed.

It works, but not quite as I expected.

It appears to not "like" solar much--cutting way back on amps, even though the dip switches are set to 14.7 volts output on the Renogy.

I do have manual control of the solenoid that feeds the Renogy.

It was distinctly NOT an easy install. The only place for it was under the passengers seat. I added some spacers under the unit as it appears there is an additional heat sink on the bottom of the unit.

Installation was with #8 wire.

I did turn the Renogy on after a night of boondocking where the "house" bank got down to 12.3 volts. At idle, charging was about 10 amps. At highway speed that went up to about 19 amps. I did not have a long drive that day.

I can still do a "poor man's" boost system should the starter battery ever be low.

The Renogy did stop the energy drain from the Telcom "house" jars to the engine. On the other hand, I could have done that with the original upgrade which gave me a dual charging path to the "house" bank--with manually controlled solenoids.

I think this may be the last "tech" upgrade I do.

[time2roll]

pianotuna wrote:
I did deliberately get the smallest dc to DC charger that I could find--for the same reason. Burning out an alternator is not my
cup of tea.

IIRC the Renogy can be set to 10 amp output if desired. Although I believe 20 amps (30 amps input) is well suited for just about any modern vehicle and alternator.

[pianotuna]

12thgenusa wrote:
I'm thinking of installing one for my 5th wheel. Concerned about the extra 30 amp draw on the alternator, long run of large gage wire (at least 6 ga) and an additional disconnect on the tow vehicle.

My oem feed to the battery bank is #8. Therefore I chose #8 for feeding the dc to DC charger, and #8 from the new charging device to the battery bank. Ampacity of #8 is 40 amps.

The path to feed the dc to DC is about 8 feet. From under the seat to the house batteries is at least 12 feet and perhaps longer. The alternator is not direct connected to the new charging device. The feed is from the starter battery.

I do have an ammeter that measures flow to and from the house battery bank. My meter falls over at 70 amps. When I had flooded marine jars (875 amp-hours), I did have occasion to exceed 70. I had added 2nd charging path from the starter battery to the house jars.

When I switched to telcom batteries (for the house) the alternator ceased charging them. Their voltage was too high I guess. I attempted to fix this by moving to an agm for the group 65 starter battery, which changed nothing at all. Hence my desire for the dc to DC unit.

If concerned about the alternator, add a switch to manually control the "feed" of power to the house bank, and a volt meter to let you know the starter battery is not being charged enough by the alternator. My control switches can be operated while I'm in the drivers seat.

My alternator is 130 amps. (stock Ford oem)

I did deliberately get the smallest dc to DC charger that I could find--for the same reason. Burning out an alternator is not my
cup of tea.

I left the oem charging path alone--and leave it switched off. It does give me the ability to have a "poor man's" boost if the need should ever arise.

[pianotuna]

.

[pianotuna]

time2roll wrote:

pianotuna wrote:
When I started to drive the dc to DC was charging at 19.5 amps. Therefore the location works.

As long as it puts 20 amps on a low battery I would count this as a success.

Many chargers will sag a bit at the top end. I assume all is normal.

The battery was not terribly low. About 8 minutes of 174 amps, which caused battery voltage to drop to 11.9. It recovered to 12.8 volts under no load.

I think that makes the install even more of a success.

[pianotuna]

12thgenusa wrote:
Have you measured your input amps? I've read these take 30 amp input to produce 20 amps at the battery.

I'm thinking of installing one for my 5th wheel. Concerned about the extra 30 amp draw on the alternator, long run of large gage wire (at least 6 ga) and an additional disconnect on the tow vehicle.

Input amps were measured "on the bench" and in the RV before the seat was reinstalled. As expected it was around 30 amps.

There was no drop in output voltage from the alternator during a short test.

I did not test with the engine running and the microwave heating.

In the bad old days when I'd load the alternator to 111 amps (running the electric side of the water heater) the starter battery would sink to 12 volts in about 20 minutes. Then I'd let the system run for 40 minutes before I'd have "another go" at heating the water.

I will be starting my last trip of 2022 on Tuesday. I'll probably try running the fridge on DC and on 120 volts. I already know the fridge is a 2:3 duty cycle.

[time2roll]

pianotuna wrote:
When I started to drive the dc to DC was charging at 19.5 amps. Therefore the location works.

As long as it puts 20 amps on a low battery I would count this as a success.

Many chargers will sag a bit at the top end. I assume all is normal.

[12thgenusa]

Have you measured your input amps? I've read these take 30 amp input to produce 20 amps at the battery.

I'm thinking of installing one for my 5th wheel. Concerned about the extra 30 amp draw on the alternator, long run of large gage wire (at least 6 ga) and an additional disconnect on the tow vehicle.

[pianotuna]

time2roll,


The dc to DC charger is stand alone. I use a Blue Sky 30 amp charge controller. It is set at a lower output voltage than the Renogy.

[StirCrazy]

pianotuna wrote:
The unit got a work out today as I stopped to use the microwave for lunch.

The micro draws 176 amps.

When I started to drive the dc to DC was charging at 19.5 amps. Therefore the location works.

what was the voltage it was putting out?

[time2roll]

pianotuna wrote:
It appears to not "like" solar much--cutting way back on amps, even though the dip switches are set to 14.7 volts output on the Renogy.

May need more panels to fully drive the solar. Have read something about not combining power inputs. Possibly more limits with solar. I would have recommended staying with the existing controller and just get the straight DC-DC.

I like separate components over these all-in-one outfits.

[pianotuna]

The unit got a work out today as I stopped to use the microwave for lunch.

The micro draws 176 amps.

When I started to drive the dc to DC was charging at 19.5 amps. Therefore the location works.

[pianotuna]

Slownsy wrote:
Why under passenger seat? It should be as close to batteries that it is charging as possible.

no room needs to be cool and dry.

[Slownsy]

Why under passenger seat? It should be as close to batteries that it is charging as possible.

[StirCrazy]

pianotuna wrote:
Hi all,

I finally have the dc to DC 20 amp Renogy installed.

It works, but not quite as I expected.

It appears to not "like" solar much--cutting way back on amps, even though the dip switches are set to 14.7 volts output on the Renogy.

I do have manual control of the solenoid that feeds the Renogy.

It was distinctly NOT an easy install. The only place for it was under the passengers seat. I added some spacers under the unit as it appears there is an additional heat sink on the bottom of the unit.

Installation was with #8 wire.

I did turn the Renogy on after a night of boondocking where the "house" bank got down to 12.3 volts. At idle, charging was about 10 amps. At highway speed that went up to about 19 amps. I did not have a long drive that day.

I can still do a "poor man's" boost system should the starter battery ever be low.

The Renogy did stop the energy drain from the Telcom "house" jars to the engine. On the other hand, I could have done that with the original upgrade which gave me a dual charging path to the "house" bank--with manually controlled solenoids.

I think this may be the last "tech" upgrade I do.

19 amps driving that not bad at all from a 20 amp setup. I wonder if the tapering amprage is because your using LA batteries who taper off amps as they charge and since you have solar going the renogy is getting a higher voltage back and tapering off. everyone I have seen tht uses them so far is using them with LFP batteries.

Steve