Undersung Tank Heaters

Discussion in 'Tech/Mech General' started by motorhomer, Feb 8, 2015.

  1. motorhomer

    motorhomer Funster

    May 17, 2008
    South Shropshire
    Our Autosleeper came with the winter pack which included tank heaters. Perhaps naively I thought this would mean that the tanks were protected from freezing in freezing weather.

    What I didn't allow for was that after only a few hours use, the leisure battery voltage dropped to such an extent that the system was powered down completely.

    So it appears that these tank heaters are only really any use when the van is plugged into mains. Not much good when staying in French aires whilst travelling through france in February!

    The problem is made worse because the Sargent control system fitted to Autosleepers, switches everything off when the engine is running - so you cannot even run the engine to warm things up! And what happens if you want to drive in seriously freezing conditions?

    My current impression is that this system of underslung tanks heated in this way is poor compared to having on board tanks that my previous vans have had.

    Or is there something wrong with my van? What have others found with this system?

  2. jonandshell

    jonandshell Funster

    Dec 12, 2010
    Sorry to say, you fell for the marketing bull.:doh:
    Despite what the manufacturers say, external tanks are as much use as a chocolate fireguard in freezing weather.
    Those heaters will draw 5 amps between them and unless you have decent batteries, flatten them in no time, as you found out!
    I insulated and put a heater element in our underslung waste tank to save draining into a bucket whilst skiing.
    It works fine, but the extra current draw is noticeable. With our 345Ah battery bank and blown air heating going 24/7, endurance is about 3 days at best.
    We are going back next week and it looks much colder now. I don't think we will last longer than 2 days.
    Normal Alpine routine is to top up the batteries with an hours run of the engine each day. This puts about 90 Ah capacity back into the battery Via the Sterling Alternator to Battery charger.
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