Redarc 40 amp DC to DC Charger issue

Maybe it is wire size, I use 1/0 DLO cable rated at 270amps so I don’t have much voltage drop.

All cabling is well within spec. The starting and house batteries are within two feet of each other and the charger is next to the house battery. Replacing the tripping breaker with a Blue Sea unit solved the problem. Input current to the Redarc gets as high as 54 amps with the ignition on without starting the motor. Settles to around 45 with the motor running. Output current stays about 43 amps when driving and climbs to about 48-49 at idle. This seems somewhat out of spec but it's certainly acceptable to me in terms of performance.

Oh ok mine is not triggered by the ignition, it is sensing voltage to trigger it on and then after about 30 seconds slowly ramps up the amps. I wonder if you got a mislabeled 50 amp unit?

S Davis wrote:
Oh ok mine is not triggered by the ignition, it is sensing voltage to trigger it on and then after about 30 seconds slowly ramps up the amps. I wonder if you got a mislabeled 50 amp unit?

Maybe? That works for me.

Ok DC/DC chargers are voltage converters. they work one of two ways (Buck only or Buck/Boost) if boosting the amps in go up as the volts out go up.
And they also draw "overhead" power.
How to limit the current so the breaker does not pop I do not know other than a longer wire.. I'd not recommend a smaller wire, between the unit and the battery Make sure the wire can haul the full 40 (in fact 50 to be safe) amps but lengthen it so the resistance limits the current DO NOT COIL IT

wa8yxm wrote:
Ok DC/DC chargers are voltage converters. they work one of two ways (Buck only or Buck/Boost) if boosting the amps in go up as the volts out go up.
And they also draw "overhead" power.
How to limit the current so the breaker does not pop I do not know other than a longer wire.. I'd not recommend a smaller wire, between the unit and the battery Make sure the wire can haul the full 40 (in fact 50 to be safe) amps but lengthen it so the resistance limits the current DO NOT COIL IT

Replacing the cheap breaker with a quality Blue Sea unit did the trick.

Teleman wrote:
. . . Input current to the Redarc gets as high as 54 amps with the ignition on without starting the motor . . .

Any particular reason you would allow your dc to dc charger to be on-line when the alternator is off-line? Most use a battery isolator or trigger wire (found on most dc to dc chargers) to prevent the dc to dc charger from inadvertently discharging the starter/TV battery when the alternator is off-line for any reason.

Teleman wrote:
Output current stays about 43 amps when driving and climbs to about 48-49 at idle.

Are you saying the output or input current climbs to 48-49a at idle?

If the output/charge current climbs to 48-49a at idle, I'd have to agree, it's definitely out-of-spec. How high did the input current go?

If you're referencing input current to the dc to dc charger, then 48-49a would seem perfectly normal with the alternator operating less efficiently at idle (higher voltage drop forces higher current).

otrfun wrote:

Teleman wrote:
. . . Input current to the Redarc gets as high as 54 amps with the ignition on without starting the motor . . .

Any particular reason you would allow your dc to dc charger to be on-line when the alternator is off-line? Most use a battery isolator or trigger wire (found on most dc to dc chargers) to prevent the dc to dc charger from inadvertently discharging the starter/TV battery when the alternator is off-line for any reason.

Teleman wrote:
Output current stays about 43 amps when driving and climbs to about 48-49 at idle.

Are you saying the output or input current climbs to 48-49a at idle?

If the output/charge current climbs to 48-49a at idle, I'd have to agree, it's definitely out-of-spec. How high did the input current go?

If you're referencing input current to the dc to dc charger, then 48-49a would seem perfectly normal with the alternator operating less efficiently at idle (higher voltage drop forces higher current).

I only turned the ignition on to measure the current briefly out of curiosity before I started the motor. The charger activates with a signal from the ignition. The output current is about 43A at higher rpms and 48 at idle like I said.

Teleman wrote:
I only turned the ignition on to measure the current briefly out of curiosity before I started the motor. The charger activates with a signal from the ignition. The output current is about 43A at higher rpms and 48 at idle like I said.

I prefer using a battery isolator because it requires >13.3v to activate the dc to dc charger. Zero chance of inadvertently discharging the starter/TV battery—ignition on or off.

I was hoping it was your input current fluctuating. Very unusual for charge current to fluctuate like that based on alternator rpm/output. The whole purpose of a dc to dc charger is to stabilize the charge process.

I have manual control of the isolation relays.