Puzzled

[RobinE]

I am loosing about 5% charge on my 300Ah lithium battery for every hours driving, according to the Victron smart shunt. There is nothing switched on except the fridge on battery, as selected by AES function of the fridge.
When stationary with engine running there is no current discharge according to the smart shunt.
The B2B charger has been removed as it is faulty and I am waiting on a replacement.
The fridge should be getting it's power from the engine battery via the relay.
On site without EHU the solar panel is maintaining the battery charge quite nicely at this time of year with limited use of inverter and 12 volt appliances.
This is not a huge issue as the replacement B2B will keep things topped up when received.
But really curious to understand what the current drain may be?
Thanks

 

[autorouter]

5% of 300Ah is 15Ah, so if it uses that in 1 hour that's a rate of 15A. That's exactly what a fridge would take if the leisure battery was the only thing supplying the 12V to its element. Does this Hymer have an EBL, and if so what model number is it? And was the B2B wired into the starter battery wire to the back of the EBL? And does the MH have a smart alternator?

 

[Guigsy]

The B2B has been removed... So there's nothing connecting the alternator to the hab battery right now?

3 way fridges are horribly inefficient on electric. They draw silly amounts of current.

 

[RobinE]

Thanks, guys, yes smart alternator, it is a 2021 Sprinter. There is a Schaudt relay fitted, EMS 03-4. I thought this would be switching the power to the fridge from the engine alternator. You have prompted me to have a look and it seems the input wires are coming from the other direction where the Elecktroblok is fitted. It is an EBL30.
So looks like the fridge is taking its power from the leisure battery? So the relay is acting as a switch between the leisure battery and the fridge?
As to how the B2B is wired, no idea, it is a plug and play Schaudt unit, many wires bound together with an input and output plug, plus to other plugs doing I know not what.
It all seems very complicated for what in my mind is a very simple application. I am no doubt being a tad naive.

 

[autorouter]

The EMS 03-4 is a red herring I think. It's normally used to control the electric step motor, and the microswitches that stop it when it's in or out. The fridge relay and the split charge relay are inside the EBL30.

One possibility is that for some reason the D+ (engine running) signal is not reaching the EBL, so the fridge relay is not switching. That might make the power come from the leisure battery instead. You could test this by removing the fuse labelled 'Kompr/AES Kuhlschrank', one of those on the left of the EBL front panel. Power from the leisure battery to the fridge goes through that fuse. If that stops the current drain then at least the problem is identified. If it doesn't, there are other possibilities, but that one's nice and easy to try.

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[RobinE]

Thank you, that makes sense..The step warning buzzer is working fine.
I will try removing that fuse when we are out in the van on Monday.
Curious that the fridge must know that the engine is running as it automatically switches to battery and back to gas again when the ignition is switched off.
When I eventually get the B2B replacement all should be well hopefully. That is a Schaudt WA121545 by the way.
Also, am I correct in assuming that the fridge will take less power from the battery directly rather than running on 240 volt via the inverter?

 

[RobinE]

I have tried this and it has proved that the fridge is taking power from the leisure battery. When the replacement B2B is received and installed I am hoping the issue will be resolved.

 

[RobinE]

Just to confirm that the replacement B2B charger has now been fitted and has resolved the issue.
When the fridge is switched to battery and the engine is running, the amount of charge to the leisure battery is reduced by around 20 amps.
Whether the fridge is taking current from the leisure battery or from the alternator I do not know

 

[Guigsy]

Just to confirm that the replacement B2B charger has now been fitted and has resolved the issue.
When the fridge is switched to battery and the engine is running, the amount of charge to the leisure battery is reduced by around 20 amps.
Whether the fridge is taking current from the leisure battery or from the alternator I do not know

When they are connected, it's all the same system. It's taking 20 amps. Provided the b2b is making more than that, the battery will get some charge.

Tip: if you can, pre-cool your fridge on mains before you go. Add chilled freezer blocks or have your beers cooled in the fridge at home. Then the fridge won't be working to bring down the temperature while you're driving.

 

[autorouter]

The fridge should get its power from the alternator/starter battery, through a separate wire with a 20A fuse on it. Very near the starter battery there should be 3 fuses, a big fuse maybe 50A supplying the B2B, a 20A fuse for the fridge, and a 2A fuse for the D+ (engine running) signal. Maybe that 20A fuse has blown, or there's a bad contact somewhere.

The fridge power should come through that separate path, so it shouldn't be reducing the amps from the B2B output to the battery.

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