Question Excessive Charging from Alternator?

[skibum42]

I have a 2013 RoadTrek Adventurous RS, Sprinter 3500 chassis. When my house batteries stopped charging while driving, I diagnosed it to a bad battery isolator. I have dual Trojan flooded 200AH 6V batteries, connected in series, rated at a maximum charge rate of 20 amps. The cores have been getting warped, so while testing the new isolator, I measured the amps going from the alternator to house batteries, discharged to 12.5V. The charge rate from the alternator started at over 60 amps, falling within a minute to 45 amps and settling in at 40 amps. This is a sustained charge rate of 2x and momentary 3x the maximum charge rate! Did I buy the wrong replacement batteries or is this a design flaw in my 10 year old RoadTrek? A DC-DC charger would be today's best practices, but there isn't room to swap one in where the isolator is. Is my best solution to find a replacement battery that can handle a faster charge rate?

 

[B52Bombardier1]

I'd get the alternator tested at an auto parts store and soon, before it boils the electrolyte in your batteries. I think your alternator's voltage regulator has died.

Rick

 

[Kevin D Pem]

The Isolator is not a charge controller!!! The idea of an Isolator is to keep the house from draining the starting battery.

The DC to DC converter is a current limiting device. It would be a mistake to think they serve the same function.
The poor man's approach is to limit wire size on the charging wire. Use silicone insulated wire if you go that approach.

DC to DC converter close to house batteries is a good answer. If you set the current setting.

Plates warp when drawn down to low as well. Take some time to diagnose the issue, as all lead has a Cx close to the same.

 

[skibum42]

I'd get the alternator tested at an auto parts store and soon, before it boils the electrolyte in your batteries. I think your alternator's voltage regulator has died.

Rick

Thanks for the response. I don't think the voltage is the issue here. The alternator is putting out 14.7, which is normal. It is a 150 amp alternator and the battery isolator connects it directly to the house batteries, so no limit on current. So, initially, 14.7v meets 12.5v (2.2v difference) and with minimal resistance, the amps flow. When on shore power, the house batteries are charged by a three-stage charger and my inverter/charger has a switch that can limit the charge rate to 12 amps. That's why I'm wondering what the battery max charge rate was for the OEM batteries. The new Lithium batteries can handle 50 amps, but I don't have that and the OEM batteries were lead-acid.