Solar charging voltage

[david lloyd]

Guys, not wanting to muddy the waters any more than they already are but, I neglected to mention that at the start of this trip away we had an A/frame fitted by Towbars 2 Towcars which necessitated the original 7 pin socket on the motorhome being replaced by a 13 pin socket. This type of A/frame requires a constant feed from the motorhome to the Towcar to keep the car battery trickle charged as the cars own electrical system operates all the lights and the electronic braking system.

 

I know (by using the discovery method) that if the Towcar is left plugged into the motorhome overnight without the engine running these electrical systems on the car are left live and will drain the car battery - as it wouldn't start the first day after fitting it! Removing the 13 pin plug from the car switches off the electronic systems - plugging it in switches everything back on again.

 

Lesson learned, the car has obviously not been plugged into the motorhome during the last five days so there is no draw from the motorhome to charge the car battery but, is it possible that somewhere in the wiring up of the new 13 pin supply this is still taking amps from the vehicle battery? My understanding is that a trickle charge should only be supplied to the Towcar when the motorhome is running.

 

David

 

 

 

[spirou]

david lloyd - 2019-08-26 9:50 AM

 

Thanks again spirou. Certainly think the low readings now are to be expected after 4 nights/5 days off hookup with (apparently) nothing going back into the batteries. We are due to leave here tomorrow and will be on a site for a few days so will get the charge required then back to monitoring what is happening back home.

 

You are getting a charge back, but less than you're using up. The question I have left is how long you were on EHU before that first day with 12.7V reading in the evening? Allan's figures for LFD say just under 13V (~12.95) with a fully charged battery at rest. So a drop of 0.2V in the first few hours suggests either you didn't charge long enough to start with or you have a substantial drain that would register a lower voltage under load even when you maybe think there isn't one.

 

I have the same 120W/victron combination with a 120Ah gel battery and have more than enough juice in the summer. But I hardly ever need more than 10 to 15Ah per day so that gets recharged quickly and I can't remember if I ever saw 6A going into the battery simply because the bulk phase is over before the sun is high enough to produce larger currents. If this is a new development after the a frame then it just might have something to do with it but I have no idea what that even looks like.