No, I'm saying it uses the transformer on hook up whether the battery is fitted or not. Off hook up it switches to the battery if fitted.

Steve

Steve is correct. I had a look at the BIP design yesterday. The BIP Power Pack SE (Part 30.65100.84) generates a regulated DC supply from the 230V when on EHU, so all the lights and pumps are supplied by a thyristor. With no EHU, the 12V side is powered by the battery (if fitted). If no battery then the Vehicle supplies the 12V via trailer plug pin 9, as long as the BIP switch is closed.

The circuitry seems quite straightforward. Relatively easy to fix but you have to take the printed circuit board out to do it. The 9V Voltage Regulator LM79L05 and the op amp (used as a comparator to sense the battery voltage) are easily available. The other components (BC337 transistors, diodes and thyristor BT145 are also easily obtained). The only problem with my BIP is that the 881-2CC relay is not working hence no awning light. This 2C variant is a Double Pole Double Throw (DPDT) relay - one pole does the awning light and the other provides a switched ground connection (not used). Unfortunately this relay is now obsolete.

To fix the problem I have connected the awning light spade terminal to output 4 on the BIP (protected by F2 - 7.5A) as this is unused. So it's on the same terminal set as the Kitchen light and 12V socket. Of course this means the awning light needs to be manually switched off for towing - so I'll put a label above the light switch by the door.

In taking out the BIP and fridge relay, I noticed that the fridge relay had a bent pin (on the coil side). Probably someone fiddled with the relay in the past. I straightened the pins carefully with pliers and re-inserted the relay into the board, I'm hoping this has fixed the problem with the fridge not working on 12V while towing (not tested yet).

My next job is to renew the trailer lead cable as it's evident the trailer cable has scraped along the road in the past (and been repaired by a previous owner). I got a 3m lead with a plug attached from EBay at £34.95 from Discount Towing Supplies - it also came with a cap to keep the rain out of the plug. I'll revert all the connected grounds to how they should be while I'm under the caravan.

Pete