Voltage drop between Charger and Batteries

[hayton55]

Just finished swapping out the old WCCO 65 amp charger for the Powermax 55 amp multi-stage charger. Prior to swap out I measured the output of the WCCO and it was 13.6v, then measured the batteries and the voltage was the same...then removed ac power and checked the batteries and they were at 12.3v...the batteries are AGM 105AH.

So I then swapped it for the new charger and when everything was connected tightly and turned on; the new charger measures 14.4v at the terminals, but only 13.1 at the batteries. I don't understand how it could be lower than what I had before. The terminals from the MH connecting to the batteries had some crud, so I had sanded all that off before connecting them to the batteries.....the original cable connections to the old charger had some of the wires missing or cut from the looks of it; so I cut the ends off and redid them so all wires would be connected to the charger. I believe I have enough of the insulation removed so as to not interfere with the connection; I may have to recheck it....

[wolfe10]

Only two choices-- resistance due to connections OR wire gauge/length giving a voltage drop.

[hayton55]

My thoughts too, but there wasn't a v drop before I swapped the units....

[HarryStone]

Are you using the same wiring between? What gauge wire and how long?

[Old-Biscuit]

How soon after install and energizing were those voltage measurements taken?

14.6V almost 0.5 hour, 13.6V almost 12 hours and then to 13.2V. ---3 stage charging


Power Max recommends 8 ga wiring

[Jzack]

Could something be drawing power after the install that wasn't before?

[twinboat]

Try cycling the Battery Disconnect switch off and on a few times. Bad contacts will cause low voltage readings.

[hayton55]

I did the measurements with the old charger a couple of days ago, it was steady at 13.6v at the charger and the batteries. I tested the batteries disconnected right before I installed the new charger and they were at 12.3. As to the question about positive wire gauge I believe its 2/0 leaving the charger but at the battery it looks larger which suggests a connection somewhere. I really don't know how it is all connected. The 12v/120v distribution box is in the bedroom up top in the corner cabinet next to where the tv is supposed to go; the charger is under the fridge and the batteries are under the steps. Strange setup but thats how it appears to have come from the factory...

[hayton55]

As to the question about something new drawing power; will that affect the output at the charger? Its sitting at 14.4v....but as I stated before at the batteries I'm only measuring 13.1 or 2.......

[twinboat]

I have the PowerMax 55 converter.

There is no way I could fit a 2-0 gauge wire in the connectors. Must be a mistake.

The battery disconnect switch will be wired between the battery and wire running to the converter/charger area.

[Old-Biscuit]

[hayton55]

Hmm, it was a guess on the wire size...however in looking at the chart the number of strands is greater than the largest gauge...I wonder if they used welding cable?

[twinboat]

Originally Posted by hayton55

Hmm, it was a guess on the wire size...however in looking at the chart the number of strands is greater than the largest gauge...I wonder if they used welding cable?

What was posted is a generic graffic.

Multi strand wire comes in many flavors.

[Jzack]

Originally Posted by hayton55

As to the question about something new drawing power; will that affect the output at the charger? Its sitting at 14.4v....but as I stated before at the batteries I'm only measuring 13.1 or 2.......

No it shouldn't. But it would definitely affect the readings at the battery terminals. There are all sorts of small 12v power draws throughout an RV.