Explode probably not.
Depends how much current it's pushing through, they can still get damn hot and the overpressure deform the casing. Ask anyone who has a APC UPS. B-) And that's with a "proper" charger in the UPS.
You'd have to be using a historic charger to get excessive voltage and curr ent, something like the old ones controlled by a lamp or by metal rectifier resistance. As long as the charger is regulated, the battery isn't going t o pull enough current to melt down or explode. The worst is a gentle gassin g, which dries SLAs out.
NT
If it were my bath lift, my battery, I would agree. However it belongs to the social services I believe and it's either gonna work now or it ain't. Testing the battery's capacity isn't going to tell me anything that I
*need* to know as neither me nor my friend will be buying a new one.Tim
The instructions linked below suggest charging the battery after each use - that's pretty much normal so I'm surprised the set you have suggest the battery can power the chair through many cycles. That is not my experience with any of them even with good batteries. It is also very dependant upon the weight of the user.
A common failure mode with SLA is to appear to fully charge but to have only a fraction of their rated capacity. Under load the voltage drops very rapidly. Having the battery run out when the user is in the bath or half way out is not a good thing. With a failing battery the lifts in-built safety feature of reserving enough power for at least one upwards lift may work correctly.
If you look at the battery Ah rating (I think you said 6Ah) that should when new support a 50W headlight bulb (about 4.5 A load) for over an hour. It should certainly stay alight for 45 minutes. If you find the voltage dropping off after 20 minutes or so the battery is certainly unfit for use.
The battery might actually be only 2.5Ah if the lift is the one here
If so 55W is probably rather too high a load for a lengthy test, something like a 12W sidelight bulb would be better.
You're right, it's 2.6Ah, just vaguely recalled seeing a 6 on the battery. ;-) Also, dunno where I dug up the ability to manage multiple lifts.
I should get a chance to test it with my weight in the next day or two and if it manages me it should manage my friend with no trouble who must be 4 stone lighter.
The battery only gets slightly warm after a couple of hours on charge so I'm not too worried about cooking it.
Tim
The deformed caseing doesn't show up very well, does on the top of the foreground battery. Note the charring and leak on the negative terminal. They've not been recycled/weighed in and just had another look at 'em. They feel sticky greasy, the badly charred terminal fell off due to corrosion, the top is pushed up a good cm and split. I'll put up another photo later.
The charger in that UPS is a constant voltage one but APC set the voltage to high for float charging and they don't take into account the temperature these batteries sit at either (40 C ish at factory settings) which should reduce the charge voltage even further.
Previous sets of failed batteries have not been as bad but the cases were all distorted. A larger rack mount APC UPS would have required major surgery to the metalwork to remove the swollen batteries from it.
As you say that was produced by a faulty charger
NT
Not faulty as in broken, the setup by the manufacturer is not adequate, one could think that batteries and UPS's is like ink and printers...
I've "got at" the UPS since that incident, reduced the charge voltage and fitted a fan. OK it now takes 30 mins rather than about 10 to switch back on after switching off due to low battery but it runs much cooler and I hope is not cooking the batteries.
You could measure the voltage while on charge. The ideal for an SLA is
13.8v - anything more could cause it to vent.
There is always the possibility that a venting battery, could have the gas ignited. There is also the possibility of an internal spark igniting the gas.
Remember the gas is a perfect mix of oxygen and hydrogen, which is about as explosive a mix of gas as you can get.
They can and do blow.
Not really. The quantity of H2 liberated is tiny, and is diluted by a room's air to far below explosive concentration. Minimal ventilation deals with it just fine.
And the OP's scenario would take far too long to dry out an SLA for hydrogen buildup to be on the radar.
NT
Having charged the battery with my old car charger, I went round to my friend's house and found the original charger!
Tim
Sorted. We need to have a thread discussing what-ifs for the next 2 weeks then.
NT
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