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Leaving van on EHU for long periods

rambling robin

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My van (Bentley Amber) charges both the leisure and vehicle batteries when on EHU - as shown on the internal control panel. Since it has this facility I hope charging does actually stop when the batteries are fully charged.

Now, for various reasons I want to leave either a fan or dehumidifier in the van running on a timer plugged in to a normal socket. Over winter this will run for a few hours each day to keep things stirred up and dry. I've noticed that even with the door wide open the toilet/shower cubicle seems to feel as though it needs more ventilation and the cab upholstery feels not so much damp as a bit clammy.

There does seem to be a mix of opinion on the question of long term hook up, but if I was on a site somewhere for 3 weeks I'd think nothing of it..........so, having answered my own question is there any combined wisdom out there that would help with this?


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When we had a boat, we left it plugged in (when on a berth), for the same reason. Dehumidifier/heaters in winter. Did this for many years, with no problems. Mind you , we did have 4 large batteries in line,.

Don't think you can "overcharge" a battery , can you?

We don't have the option of EHU for the van, so just leave dry crystals, to do the job. These do work, as we checked last week, having left van for some time, There was moisture in the containers


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I have used a dehumidifier in the garage over winter and if ambient temperature drops too low (I think below 5 deg C is when it gets critical) the evaporator mesh of dehumidifier can ice up.  Mine did this spectacularly and obstructed the fan, so its motor burnt out.  In order to run dehumidifiers continuously in winter you probably need a heater as well, set to maintain 5 degrees or higher.  Mine (in the damp garage) collected quite a lot of water so I ran a tube to a drain rather than have to keep visiting to empty the tank. 


It's possible that it collected all this water because I was effectively trying to dehumidify the atmosphere of Lancashire, so whether a dehumidifier in a non-leaky motorhome over winter is really necessary is a moot point.


Our MH now lives outdoors in Suffolk, so less moisture but more risk of freezing.  So far it seems to be doing fine without either heating or dehumidifier - and doing without either will hopefully reduce the risk of vermin infestation because the warmed shelter won't appeal to them.


As far as battery charging is concerned I left our Hymer MH on continuous EHU in storage for most of its life without harm and the Schaudt Electroblok  charger maintained the gel batteries extremely well with no loss of battery electrolyte or other problems.  Now I have solar panels and the MH is outside I rely on them to maintain battery charge and don't bother with EHU.  That seems to work perfectly too.


Whether continuous EHU in storage would be safe for your MH will depend of what type of battery charging system is fitted and whether that backs off to a maintenance voltage and maintains that once the batteries are fully charged.


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I leave our Autotrail on long term hook up, to keep both 110ah batteries and the vehicle battery topped up, also have a small convector heater to keep the temperature above freezing. Have done this for many years, without any I'll effects, also have 2 sonic mice scarers running, all for very little cost.

Previously had a Caravan, which I did not have EHU, the battery failed, and we got bad mould on the soft furnishings. No contest.

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I see no reason not to leave the hook up in place for a long period...unless of course there is the chance of overcharging your batteries.  So assuming your regulators are good then I would think it would be fine.

The comment about dehumidifiers icing up is correct in part.  Not all dehunmidifiers do this.  Try this one...

It is a dessicant dehumidifier as differentiating from a compressor type and works at lower temperatures.  In general compressor dehumidifiers efficiency drops off at around 15 degrees whereas a dessicant type will operate more efficiently  than a compressor type at those lower temperatures.   We have the model I posted in the link and using it in the conservatory on damp winter days the humidity level drops very quickly and the temperature soon rises to a comfortable level.  It even has a setting for airing clothes it is so efficient.
I'm not sure if you can leave this type on on a timer as it has flush fit press buttons for on/off and differing duration (2/4/8 hrs etc) and humidity settings.  Basically once the mains power is off the next time you want to use it it requires switching on......switch mains on....switch dehunidifier on.  It won't sit there hibernating waiting for mains power from a timer.

As for a fan on I don't see it will achieve anything in terms of humidity.  All it will do is circulate the air which is not really going to achieve anything in terms of damp control.  If you wanted to go that route I would couple it with one of these...

However cycling from warn to cold is likely to increase the condensation/damp issue.

Oh and there are those who will say dehumidifiers in a MH are somewhat pointless as there are so many vents all you are doing is dehumidifying the air and sucking in more humid air through the vents to replace it.

Just my 2d thoughts on the subject.
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Thanks for the various observations - I guess there's no right answer, each situation is different.


I have a couple of small rechargeable desiccant d/h things in the cab area together with a number of old winceyette sheets over the dash and seats which get dried out once a week. They also pick up any condensation running down the inside of the windscreen and stop it puddling a the bottom of the screen. The habitation cushions live behind the sofa over winter.


Certainly running a dehumidifier will result in trying to dehumidify the planet. The output from the d/h compressor is both warm and dry, I do understand the issues with warm/cold encouraging condensation.


My general feeling is that the natural ventilation in the van is fine, but the air is stagnating in certain areas which is why the fan seems to be a good compromise as it will move the air around without increasing the temperature.

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