Minivator Stairlift Issues With Batteries Keep Going Flat


Postby Canutakethis » Thu Feb 16, 2017 11:10 am

Mother in laws stairlift secondhand was working fine for 6 month then stopped working changed the batteries working fine for 2 months then stopped again called a stairlift company out who serviced it said batteries where no good so pain out £145.00 for service and new battery's worked fine for 3weeks stopped called them out again and told need a new psu charger so she paid out another £120.00 worked ok for another 3 weeks then stopped told battery's are dead said he never seen battery's that flat no reading wot so ever checked it all over power from psu ok power fine all way down track could not find a problem anywhere and he looked as I said battery's covered so no call out charge he spent nearly 3 hour s trying to find a fault so he could charge a call out and wot ever else i.e. Part that's wot I believe he said if it happens again it would need a new pc board and they cost from £400 up wards now 5 weeks later yep stopped working again grrr any one have any ideas please as to wot the problem could be as the old girl is 85 and really started to relying on the stairlift thanks
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Postby ericmark » Thu Feb 16, 2017 10:39 pm

I also had problems with stair lift batteries. The problem with valve regulated lead acid batteries (VRLA) is you can't top up water so over charging can kill the battery.

It's a fine line between leaving the battery flat so you get sulphation of plates, or over charge and it dries out, so what most chargers do is use a stage charging system.

What it does is charge flat out, (stage 1) until voltage is around 14.4 volt, then monitor the current while holding volts at 14.4 (stage 2) and when current drops to around a 1/20 of the amp hour rate of battery, then drop the volts to 13.2 volts (stage 3), also a timer in case the battery is faulty which will drop it to 13.2 after around 8 hours should the current not drop.

There are other methods like pulse charging, but unlikely that would be used with a stair lift.

However a much cheaper method is to simply charge at 13.4 volt and hope the lift is used often enough to stop over charging. With 13.4 volt battery life around 2 to 3 years, with stage charging more like 8 years.

Now with fork lifts the last stage is switch off, rather than an equalising charge, there are variations, with a hedge trimmer they say in instructions only charge for 16 hours, and use a rather hit and miss system.

I would guess the charger has got stuck on one of it's stages and is either over or under charging. For the repair man the problem is how do you monitor a process that takes 16 hours in a 1/2 hour call out slot?

Mothers lift has three charging points, so very easy to put a meter on one of the two not in use, just did it and it shows 29 volt DC, that's for 2 x 12 volt batteries, so 14.5 volt each, well over the 13.2 volt required to maintain the battery, I will assume something inside the chair drops the voltage, but would not be surprised to find no voltage dropper.

So step one measure the volts to stair lift, if like the Stenner we have, everything runs on battery, then it's recharged once parked.
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Postby Canutakethis » Fri Feb 17, 2017 10:44 am

thank you for the info so I take it I will have to get a new pc board for the lift then ? as I was told it wil charge anywhere on the run where it stops not just on the bottom or top as I thought it did
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Postby ericmark » Fri Feb 17, 2017 10:24 pm

With mothers lift there are only three charge points, to charge anywhere it would need a pick up rail or flex the length of stair lift, not impossible but unlikely, the idea is in the event of a power cut it will still work, unlike a lift which you can't use in the event of a fire you should be able to use stair lift.

I am sure my mothers Stenner stair lift uses a simple 29 volt to charge battery which likely explains the short battery life, as explained it could have a complex charger, but unlikely.
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