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Ping Burgerman.....

Doki on uk.rec.cars.maintenance said that you may be the one to ask about this my friend, so here's a cut 'n' paste from the message I posted there earlier this afternoon:

Been asked to look at a friend's wheelchair because they're finding that a full charge only lasts to the shops (a lot less than half a mile) and he has to be manually pushed back. They only recently bought the chair from a friend of a friend of a friend of theirs because the guy who used to own it has now died.

Anyway, the batteries currently fitted are these

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Europa 12V 33Ahones, connected in series on the chair to give 24V. Tested with a digital multimeter each battery is reading 12.8V off load and when connected together for use on the chair, total voltage is 25.6V off load. The charger is an electronic type and has LEDs to indicate the state of charge and when connected, the output of the charger measured across the battery terminals is 28.8 to 29.1V.

Unfortunately, I can't measure the current output of the charger (rating plate says it gives out 5A) because it connects to the control box (steering joystick-type thingy) of the chair by some sort of 3-pin DIN-type connector - and even while I'm typing this I've just realised I could measure it at the battery end rather than output of the charger end. What a bleedin' plonker I am eh?

Anyway, the batteries are sealed and, even if they weren't, there's apparently no liquid electrolyte to draw up into a hydrometer to test each individual cell - the acid is in gel form, I believe. There are labels on the batteries stating "19 June 03" so they are four and a half years old.

For this reason alone, I'm suspecting the batteries as being the problem rather than anything else, but I'm also concious of the fact that 118 quid for new batteries is not an inconsiderable sum for my mate to pay out - especially if I'm wrong and he still has to pay to get the fault fixed so can anyone give any pointers to anything else, or confirm my not brilliant diagnosis that it's the batteries?

Any thoughts on that Burgerman?

Cheers, John

Reply to
John
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This is completely off topic of couirse which is perfectly normal on here!

Off load voltage directly after a charge sdhould be higher than that. Typically 13.4 or thereabouts or higher. 12.8 or above is typical after charging and then testing the next day after 24 hours after the surface charge has gone.

But this only gives you a "state" of charge. So if this 12.8 is after some light use or after a day then they are fully charged. The charger if its the correct charger for deep cycle batteries and for traction use will pull the voltage up to 28.5v or so for about 30 mins at the end of the charge cycle to equalise all the cells. After that it just holds the voltage at around 27v permenantly on "float" charge.

None of this tells you the batteries remaining capacity though!

A battery that is correctly charged every 24 hours, and every daily "cycle" will give x number of cycles depending on several things.

One thing, how long a discharged battery is left discharged matters a lot. A battery left at less than 90 percent charged starts to "sulphate" internaly. This slowly reduces the batteries capacity. And does it faster if its left discharged to any large degree. Remember that batteries naturally use a small amount of charge just sat doing nothing... When sat in a switched off powerchair they are still being drained slowly by the "computer brain" under the seat. So left for as couple of weeks with no charge means flat or partially flat batteries... So damaged.

Plus...

Good deep cycle batteries will give 300 cycles or days if used and charged every night with a 80 percent depth of discharge.

10 percent = 10k approx cycles 20 percent = 2.5k 50 percent = 1k 60 percent discharge and you get areound 600 cycles or 2 years. 80 percent (as I average due to a lot of use and you get 300 or about a year if lucky. 90 percent = 75 charge cycles. 95 percent = 10? 100 percent most likely a couple if lucky.

Now my powerchair batteries are 75 amp hour. Yours are about half that so you can expect reduced battery range as well as life.

So most likely you need new batteries due to misuse. But you wont ge all day range and good battery longevity with batteries that size.

The charger is an electronic type and has LEDs to indicate the state

Yep thats correct. Its designed to equalise all the cells after a deep discharge - helps keep all 12 in balance. Its a controlled short term overcharge that isnt enough to boil the electrolyte.

You dont need to measure it. It will give 5 amps for the bulk of the charge, as the volytage reaches a certain level it switches to a lower rate that is voltage dependent and then at the end gives a small burst to equaliuse the cells and then moves to a continual float charge. ts logic controlled and they seldom fail unless totally!

Theyre dead Jim

Its a combination of the batteries (which are at least chemically aged after that time) and a chair thats designed for light or indoor use.

Reply to
Burgerman

Well Burgerman, that's a very comprehensive and superb reply! Thanks very much for that mate, I really appreciate it. I owe you a pint :o)

John

Reply to
John

i used to work for a firm that sold power chairs (until 6 yrs ago) and batteries were the biggest problem we had, every different person at every different supplier and maunfacturer we spoke said something different, although our usual advice was to put the chair on charge overnight every time it was used and if it was not used for more than a week charge it for

24hrs, also to charge it for 24hrs every month anyway.

as usual the exception that proves the rule was the chair i saw one day that had 5 year old batteries where the owner had been told by the original dealer to run the batteries right down before charging them and they were still going strong!

BTW Burgerman, we did have great fun one saturday morning following the instructions on your website and changing the settings on one of our F55s then rolling around the car park on the rear wheels and anti-tips turning at full speed :-)

james

Reply to
john doe

If you scrap all the overweight bits, move the seat back to a more sensible position like mine, rewind the 4 pole motors to make them draw more current, fit the bigger 100 amp controller wheeliies are easy at all speeds not just from a standstill!

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Reply to
Burgerman

As an aside Halfords do lesure "deep cycle" batteries. With a 2 year warranty... Now they are shit as far as real deep cycles are concerned but cheap. I got

2 with 50 percent off (ask for a trade card first).

They cost me 47 quid each. Now these are 75ah so yours would be cheaper. But GOOD deep cycle batteries are about 100 to 200 each. The halfords ones so far are lasting 2 months a pop... But they keep giving me new ones so who cares. I normally use optimas

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though but even though I sell them (or used to) they are still expensive.

Reply to
Burgerman

So, how is the Voyager going ?? Still looking shiney and dent free!

Tim..

Reply to
Tim..

5k miles, looksd just as clean and polished as ever.
Reply to
Burgerman

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