EHU connected & charging, Truma Ultraheat on...but engine battery now "flat"...how come?

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MH04RMV

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Cheyenne 632 SE
Hi All,
Given the cold snaps of late, have had the EHU connected to house supply over the last couple of weeks with the Truma Ultraheat on, set to number 7 and either 1Kw or 2Kw with fan speed of 2 (to hopefully prevent pipes from freezing, given the other thread about using antifreeze).

Went to try and start it up last night, and the engine battery wouldn't even try and turn the engine over (subsequent check of the display panel was showing ~10.7V for engine and ~13.7V for leisure).

I had thought that if the EHU was connected, the heating and any charging (for both leisure and engine batteries) would be "covered", with no drain from either the leisure or engine battery?

So...
1) Is this just a case of "sudden battery death" following a couple of cold (minus °C) nights/engine not having been run for a couple of weeks?

2) Is running the heating at such levels too much for the EHU to cover on its own, so also taking some power from the batteries?

3) If yes to 2, why would the ENGINE battery be drained first and not the leisure battery)?

4) Could it be that the engine battery is just old (I don't know how old it is), and maybe its time has come (linked in to the cold nights)?

5) Is there perhaps something more fundamentally wrong with the electrical system?!

Appreciate any thoughts/suggestions you're able to provide.

Cheers,

Rich.
 
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PS
I should add that the charging switch on the internal distribution board is "On"...
 
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The heating system only takes 12v power to run the electronics and the fan so no excessive draw.
The engine battery is seperate and does not run the habitation electrics.
First thing to check is engine battery getting charged when on EHU most vans do this automatically but not all. I think you may have a Sargent system and they may need to be set up correctly to charge the engine battery.

With the engine battery that low fingers crossed it hasn't taken out the airbag ecu.
 
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Vic said:
What van do you have?
Click to expand...
A Cheyenne maybe?
I see this when using my laptop.........


1638018615100.png

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Hi All,
Thanks for the input.
Yes, it's an Autotrail Cheyenne 632 SE (2004), with a Sargent PSU 2007. All MCB's "on".

When I checked earlier this (Sat) evening, the engine battery was showing as 8.7V 😥
I've put it on a "recovery charge" cycle via separate charger, but suspect it may be dead now & new one will be required.

A spin-off question following Lenny HB's note about airbag ECU's...presumably a garage can plug a box of tricks into the main system port (wherever that may be, and presuming there is one), to see if any error codes might be thrown up?

Cheers,

Rich.
 
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Rich H said:
A spin-off question following Lenny HB's note about airbag ECU's...presumably a garage can plug a box of tricks into the main system port (wherever that may be, and presuming there is one), to see if any error codes might be thrown up?

Cheers,

Rich.
Click to expand...
No need. If the airbag ECU goes you will get a red warning light permanently alight on the dashboard. It will be am MOT failure.
 
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Rich H said:
Ah ha...OK, thank you.
Click to expand...
We had an ECU failure 2 weeks ago. It threw the Fault Code U172687 Sensory & Diagnostic Module, Body Controller & Instrument Panel, lighting the Instrument Panel like Blackpool Illuminations. Airbag & Seatbelt Pretensioner Lights on Instrument Panel, audible alarm every 30 seconds, 'Check Handbook' message scrolling across the Instrument Panel and the dashboard warning light [to the left of the Hazard Flashers, opposite the passenger's knees!] lit up with bright yellow light and 'X 2' message overlaid. Difficult to ignore or to be blissfully unaware of the problem ...

Steve
 
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Rich H said:
A spin-off question following Lenny HB's note about airbag ECU's...presumably a garage can plug a box of tricks into the main system port (wherever that may be, and presuming there is one), to see if any error codes might be thrown up?
Click to expand...
Shouldn't be a problem on your van only appears to affect vans around 2014 to 2019.

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What causes the failure? Is it just a low voltage or no voltage? I'm asking as I was going to fit a new cab battery before we go abroad again.
 
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In many Autotrails the engine battery and habitation battery electronics should be considered separate.

If the engine is running the habitation system gets a charge from the alternator via a relay in the Sargent PSU, as well as the engine battery being charged.

On hook up, or if you are fortunate to have solar, your habitation will be charged, but there is no reverse link to top up the engine battery. Meanwhile alarm systems and other nominal stuff from the vehicle will gradually drain the engine battery. A few, but certainly not all, of the Sargent PSU thingys do allow the engine battery to be charged from EHU and / or solar, but you'll need to read the manual to check if it has that capability, and how to configure it. Certainly my extremely pants system did not have that option.

To avoid this problem, when on solar or EHU fit a Vanbitz Battery Master. A very simple bit of kit that when it detects the habitation voltage is a small bit higher than the engine, it will trickle charge at less than 1A, just enough to keep the engine from flattening when not in use.
 
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Richard n Ann said:
What causes the failure? Is it just a low voltage or no voltage? I'm asking as I was going to fit a new cab battery before we go abroad again.
Click to expand...
Low voltage and I think you shouldn't leave the cab battery disconnected for more than 15min.
 
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Hi All,
Took the battery to local car parts shop, and they confirmed that the battery had a dead cell, so I think the first couple of cold nights must have done for it.
New battery going in this afternoon, so will keep an eye on the panel voltage numbers and see if there's any significant drop, which might also indicate bad earth/drain somewhere (the only thing that is "on" (that's connected to the engine battery, as far as I know) is the radio clock display. Might be able to turn that off too.

@ Kannon Fodda - thank you for the info about the likely lack of charging to the engine battery from the Sargent PSU - I'll have a look at the bumph I was given from previous owner and see if there's anything in it that relates.
Will also check out the battery master, thanks for the tip.

@ Stevewagner - heating has only been on to (hopefully!) prevent any frozen pipes/fittings etc., as I had a separate query/thread about whether Star Bright -46°C antifreeze could/should be used in the potable water system (inc. water heating tank) - seems it's not suitable (for the tank), so will see if I can put an air blower system together (similar to Floe) to blow out any lingering water while draining down.

Cheers,

Rich.
 
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I have a Cheyanne 740s and the engine battery is very low showing 1.9v on the panel above the side door. I read earlier, elsewhere, that when EHU connected I should make sure the Seargent is switched on. I have done this and just left the right hand breaker on, which is for heating and charger. I have switched the other 2 off.
The control above the door. I pressed the left button and a blue light lit. Pressing the right button it reads Vehicle battery 1.9v plus I pressed the botton of three to the right and it gives readings of amperage, water and lots more. I have switched the Alarm off so not using any power.
I have left it with the left button pressed and blue light on and the right button pressed with the reading Vahicle battery 1.9v.
There is however no light staying on.
It has been like this for 3 days and the vehicle battery is not charging at all. Can anyone tell me where i am going wrong or give any info at all?
Many thanks and I must join this group.
 
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CJN If the vehicle battery is down to 1.9 v it is probably finished and is to low to allow the van charger to operate. All you can do is remove the battery see if it will take a charge from a separate battery charger .

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I've got a Sargent system fitted to my 2021 Auto-trail Expedition PVC, and like Kannon Fodda I also thought originally that it would only charge the habitation battery on EHU, but I found that it can also charge the vehicle battery. I needed to turn the display on above the door, and then select "vehicle battery". (Whilst it will charge the habitation battery with the display turned off, it has to be turned on to charge the hab battery). It is not possible to charge both batteries simultaneously, or have any level of smart or automatic charging. It's basic but sort of does the job.
 
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THanks for all advice. I have also been told I can use a leisure battery after removal, to jump start the engine and then see if it will charge the vehicle battery. If it doesn't i will buy a new battery.
 
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Make sure that if and when you get the battery charged or replaced you find the cause of it going so very flat in the first place, was something left on or was it left uncharged for a long period ? (if you fit a new battery and it then gets to be that flat it could be damaged)
 
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Sargent systems vary so you need to look documentation for your particular setup. For example my 2013 Auto-Trail Mohawk has the EC500 PSU and EC480 control panel and in the menu there is a setting for smart charging with EHU and Solar where it will charge the Hab batteries then the Cab battery, or you can set it to just charge either and not the other. The other thing with mine is I find it better to shut the whole system down due to the high parasitic drain of the EC500 PSU, all charging then goes to the Hab battery by default.

Sargent systems don't all work in the same way.

The best way to keep the engine battery charged I have found is to fit a VanBitz or equivelent battery master.
 
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