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Switching for a S+/D+ connection to a motorhome Dometic AES fridge

I have successfully installed a Smart Solar MPPT150/35, BP65 and a BMV 912 to my motorhome. My plan was to connect the output from the BP65 (with suitable on/off voltages set) to the S+/D+ input to my Dometic AES fridge so that it would be powered from the battery bank when solar/battery conditions allowed. The fridge works on battery power when the engine is running (with the D+ switching connection from the alternator) but I have had no success so far with switching using the S+ connection. I would be very grateful for any advice/help for this type of connection/configuration.

MPPT - Solar Charge ControllerBattery Protect
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1 Answer
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kevp answered ·

Simon, I have just been doing the same thing. However, I have the smaller 75/15 MPPT which has a load output. This means I can use the AES setting on the MPPT to deliver 12v when sufficient solar is available. I found I needed to install a diode to prevent my electric step closing and satellite dish automatically stowing. I was quite surprised how much 12v the fridge uses though, it draws 10A continually (vs 400g of gas per day) so it is only an option on the best summer days.

I should say that I have a D+ only fridge hence the interacting with the dish and step. If you have a designated S+ connection then that should be straight forward.

One thing I did read recently was that there is a time delay (15 mins) after using the fridge on 12v via the D+. This is to stop the fridge switching to gas mode when you stop to fill at a petrol station. If you have had the engine running prior to trying to get it to switch, it could be that preventing the S+ working. Perhaps you could try supplying S+ after the van has been parked for a while. You only need switching current on the S+, the power should be provided via the EBL large DC cables directly to the fridge. Will you be using a manual switch or something more elaborate?

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