Which <span class="highlight">solar</span> controler to buy ???

You don't say if you batteries are Charged when the reg is only putting out 4V. If so then that is probably OK. If batteries are flat and you only get that then yes maybe reg is done. I'm also not sure if you are talking about a reg mounted in your van or if panels are portable. If so then Jcar do regulators that do the job.

Tim,

If you've got about 17V before the regulator, that suggests the regulator is loading the solar panels correctly.

The 4V after the regulator (i.e. at the battery) is a worry though. Could be the battery is crook, could be a short in the wiring, could be the controller is crook.

Before going straight to a replacement controller I'd suggest investigating further by disconnecting the controller and monitoring battery voltage and current while charging using a standard 240v charger. This will point to any battery or wiring issues, and may breathe life back into the battery for use another day.

Starting with a full battery and no obvious problems, I'd then reconnect the solar regulator and monitor for any peculiar happenings, especially excessive current flow out of the battery. If you do see signs of distress I agree that a replacement controller is probably the way to go. I can't make any specific recommendations, beyond favouring an MPPT type with ample current rating.

HTH

Cheers

John

Tim,
What is the voltage measured at your batteries and was the regulator connected to them when you took the measurement?

If that 4V is measured WITHOUT the batteries connected to the reg output, that was a pointless exercise. Connect it to a batery and monitor the voltage, or better still the charge current.