Renogy 20A dc to DC report

theoldwizard1 wrote:

otrfun wrote:
The 3-4a drop in output current at idle vs. driving would concern me. This potentially indicates the alternator is unable to sustain the proper current/voltage at idle. In other words, the dc to dc charger may be overloading the alternator at idle. Every dc to dc charger I've installed has exhibited negligible to no drop in input current to the dc to dc charger when the engine is idling at, say, 750rpm vs. driving at 2000 rpm.

It is not an amperage issues.

As long as the alternator can sustain the MINIMUM input voltage to the DC-DC charger, it is a non-issue. Most of these chargers have a way to determine if the engine is running or not to prevent discharging the vehicle starting battery OR they need to be wired to a KEY-ON circuit.

An adjustable minimum input voltage might be useful.

The Renogy ignition trigger lead and/or commonly used battery isolator accomplishes would you're describing. If the Renogy ignition trigger lead detects a "nominal" 12vdc, the charger turns on. If the 12vdc goes away, it turns the charger off. A battery isolator operates in a similar fashion, but it's much more voltage selective. It closes its relay (providing power to the Renogy dc to dc charger) when voltage reaches approx. 13.3v (alternator active) and then opens it (releases) when voltage drops to approx. 12.8v (alternator offline). These are simple on/off devices.

What pianotuna is describing is a 3-4a drop in output charge current at idle (vs. driving). Neither the Renogy 12vdc ignition trigger lead, nor a battery isolator would cause this. They simply turn the Renogy dc to dc charger on or off. Nothing more, nothing less. They do not interact with the Renogy's internal voltage/current regulation circuitry in any way.