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Author Topic: Wheelchair power supply  (Read 723 times)
KD5AIU
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Posts: 12




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« on: September 09, 2009, 10:06:19 AM »

I've been "charged" with repairing or replacing a 24Volt 5Amp charger for a mobility scooter. Would hooking up two 12V battery chargers in series work until I find another supply?  

I've read the pitfalls of hooking two supplies in parallel but wonder if power would be pulled evenly from both supplies if in series.

I'll break open the factory charger and look for any obvious faults but have no experience with such repairs and may be back for advice on that topic.

Thanks for any help.
Dave
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KA5N
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Posts: 4380




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« Reply #1 on: September 09, 2009, 10:52:40 AM »

The cautions against series connecting power supplies mostly applies to REGULATED supplies.  If the power supplies are unregulated probably nothing much bad will happen.  Now replacing a battery charger designed for a particular function (charging the chairs batteries)with another charger designed for different types of batteries may open one up for new problems.
First I would contact the service department of the chair company and find out what a new charger would cost and the cost of repairing the one you now have.
You may decide it is not cost effective to try to do it yourself.
If you decide to tackle the job (and you admit that you don't know much about the charger) try to find out as much as you can about how the charger functions.  There are chargers and then there are chargers, some are simple and some have sense circuits to prevent damage to the batteries and on and on.
You can always take the batteries out and charge them from a current limited power supply and as long as you monitor the state of charge, safely charge them.
This will soon become a big bore.
How many times have I heard someone say: " It don't
work now, so how much damage can I do?"
Allen
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K5LXP
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« Reply #2 on: September 09, 2009, 12:05:43 PM »

In general you can charge two series batteries with an isolated charger on each one independently.

The key issue isn't if it will "work", it's what kind of chargers you intend to use.  "12V battery chargers" isn't specific enough.  If you have two 12V gel cel chargers rated appropriately for the Ah size of batteries you're attempting to charge, you're fine.  If they're two different capacity units or not made for gel battery topology (i.e. a car battery charger) then you will run into problems with fully charging, overcharging and/or keeping the pair balanced.  The insult to injury would be to wreck the pair of batteries trying to make do for a while.  This would be one of the "how much damage can I do" situations KA5N alluded to.

The reason they use a series charger is you put the same current through both batteries for the same amount of time.  If the batteries are reasonably close to being matched, they should both come up together.  By charging them independently you can't assure they're both charging at the same rate over a given period of time.  If they're the right chargers, both the same type, and you allow each to charge to completion, then you should be OK.  Or if you only have one charger you could do one at a time, again making sure one has charged to completion before charging the other and not using the chair until both have had equal charging.

The right answer is a replacement 24V gel battery charger, whether it's the repaired original, OEM replacement or suitable substitute.


Mark K5LXP
Albuquerque, NM
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WA3SKN
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Posts: 5480




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« Reply #3 on: September 09, 2009, 02:07:08 PM »

This is a "theory vs practice" problem... and I wouldn't do it.  If everything is perfectly balanced, all would be well.  But, if they are not, it would be easy to draw too much current from one unit and breaking it... and possibly the other unit too!
73s.

-Mike.
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N5RMS
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Posts: 37




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« Reply #4 on: September 09, 2009, 05:34:06 PM »

Go to a sporting goods store (Cabella or Bass Pro Shop)or buy one online.  They usually have 24 volt battery chargers for trolling motor batteries (fishing).
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K9YLI
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Posts: 863




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« Reply #5 on: September 10, 2009, 06:42:53 AM »

I would try and fix it.   Its already  broke so how much more broke can you make ity.

and battery chargers are usually quite simple and its even possible to follow the lines and draw a schematic.

mostly  its a transformer and  2 diodes to give  a dc  ripple out put.
pusle charging does a better job than filtered  DC.
and diodes are the weakes link.
check the transformer output for 26 volts or so  AC.

then check the diodes with an ohm meter.  
they read  high one way and reasonably low the other.
exact readins are not critical.  and they shoud be close to each other.
  several megs  one way and  couple hundred K  the other.

Of course if its   economical to have repaired then  don't mess with it. .....
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KC0RBX
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Posts: 165




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« Reply #6 on: September 10, 2009, 09:46:04 AM »

You will have no problems.  This is done on industrial hydraulic scissor lifts all the time and almost predominantly.  Locomotives have the same thing to achieve their desired voltage on diesel electric engines using 8 volt batteries in series.  It will work just fine till you get a 24 volt battery.
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KA5N
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Posts: 4380




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« Reply #7 on: September 10, 2009, 10:00:33 AM »

"I would try and fix it. Its already broke so how much more broke can you make ity"

OK! Now I've heard it another time.

To KC0RBX
He asked if he could parallel two 12 volt chargers,
not two 12 volt batteries.  The charger is broken not the batteries.

Allen
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K1CJS
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Posts: 6034




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« Reply #8 on: September 10, 2009, 11:42:38 AM »

If you're not sure about fooling around with the battery charger you've got and can't get a 24 volt charger, go into the battery box and see if the batteries are 12 volt batteries.

If they are, get two sets of quick disconnects and put a set of them on each battery--and the 12 volt charger you've got.  You HAVE TO charge each battery separately if you set it up that way, but it could be done.

Of course, the proper way is to fix the charger or get a 24 volt charger.  You can take the connector cord off the bad charger and put it on the new one.
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N6AJR
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Posts: 9908




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« Reply #9 on: September 10, 2009, 11:55:46 AM »

my mobility scooter uses two 12 volt batteries, but they are in parallel.  can you take them out or unhook them and charge as 2 seperate 12 v units?  call the company and order a new charger.. ?
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