60a DC-to-DC Charger Powered by 220a Alternator

DC-DC converters can put out much higher voltages than their supply voltage.

Be aware that just because your alternator is rated at 220A, it won’t always supply that much. At idle there likely won’t be anywhere near 60A available for the charger even with the vehicle batteries charged.

Anyone know how many amps a 220a alternator on a Cummins is capable of producing when it’s idling (~700rpm)? I measured 80a of charge current about a year ago when the batteries were discharged quite a bit.

Your going to have to measure that one for yourself for your vehicle.

It will vary a lot depending on battery age and condition, the temperature of the alternator and air around it and what accessories may be running.

Generally, the alternator is "geared" to run just fast enough to handle typical operating loads at idle like engine electronics, lights, fan and perhaps A/C without drawing the battery down..

Just because it may be a "220A" alternator, doe not mean it can and will produce all 220A at idle OR for LONG PERIODS OF TIME..

It is intended to provide short intermittent bursts of current to cover spikes like your power windows and such. We are talking seconds to a few minutes, not hrs of heavy use.

I've been researching this myself. I have been looking at Redarc DC to DC chargers. Etrailer has a lot of information on installing which you may find helpful.

dccamper wrote:
I've been researching this myself. I have been looking at Redarc DC to DC chargers. Etrailer has a lot of information on installing which you may find helpful.

Renogy has a 50 amp for a lot less money than the Redarc 60 amp.

jkwilson, thanks, good to know a dc-to-dc charger is capable of voltage compensation.

Gdetrailer, thanks for the explanation. I was aware of some of the various limitations and concerns which is why I posed my question. With dc-to-dc chargers becoming more mainstream and the Ram Cummins being one of the more popular TV's, I was hoping there may be more specific info in regards to what this alternator (and/or a Ford/Chevy HD alternator) is or is not capable of.

FWIW, I believe the stock alternator on a Ram Cummins is rated at 160-180a. Our truck came with the optional 220a alternator. Wouldn't this extra capacity significantly reduce (not eliminate) any concerns about an additional 60a load on this alternator---even at idle?

Do you really need 60 amps of charging for your camper batteries while driving? Is the DC-DC charger going to be your primary means of charging them? Or will you be using the DC charger to keep from running your camper batteries down while driving?

I run my fridge in AC mode from an inverter while driving, and that’s about a 28 amp intermittent load. I’m using a 40 amp Redarc DC charger to keep the camper battery charged up. If we dry camp for a night or two and run the camper battery down, the DC charger might need to go to full output for a while when we start driving again. The input to the charger is fused at 60 amps, so it will never exceed that. With the size of the wires I installed to feed the charger, I doubt it will exceed 50 amps. I haven’t monitored the amperage output from the charger while driving yet, but I have forced it to supply its full 40 amps while idling, and it will do it.

Consider carefully what you need the DC charger to do for you, and size it from that. Mine isn’t my primary means of recharging the camper battery. If we’re needing to use a lot of power while dry camping, I will get my Yamaha 1000 generator out and let it provide that power and charge the camper battery as well.

:):)

60 amps is probably higher than the designed add-on accessory load for the vehicle. Assuming it is a diesel the grid heater or glow plugs may also add significant 12v load. You could reduce the issue by not immediately turning on the A/C and running lights etc. Or to add a switch to delay the 60 amp charger until the start batteries are mostly topped up. Best would be to measure or monitor alternator output in extreme load conditions to see actual existing load.

Worst case the alternator quits??? For most people I think it is best to limit these to 20-30 amps.

The documentation should explain the voltage and current requirements to produce 60 amps at 14+ volts. I speculate it may draw 80-90 amps depending on conditions.

If you plan to run this at idle for an extended period I recommend a high idle modification.

Look at the install instructions for the unit you’re considering and see what fuse rating they recommend on the charger input circuit, and assume it will at least get close to that at times.

:):)

otrfun wrote:
Thinking about installing a 60a dc-to-dc charger in our truck camper. Have plans to power it with the 220a alternator in our truck.

How big is your current alternator ? It is probably sufficient to power a 60A DC-DC charger.

otrfun wrote:
Also have a question about how most DC-to-DC chargers operate.

Without getting into too many gory detail:

• Incoming DC is converted to AC by switching it on and off. This is done much faster than the 60Hz that we get from the power company so that they can uses smaller transformers.
• The transformer boosts this AC voltage to something higher than required to charge batteries (18VAC-24VAC ?)
• This AC voltage is converted back to DC
• Some kind of "smarts" controls the output DC voltage to the appropriate amount.