Battery / chair storage

[Burgerman]

Best way to keep any battery healthy long term is to keep it on a low accurate float at a cool temperature.
This way a battery can stay healthy for a decade or more.

To do that is problematic.
The only way most people have to do this is to charge a wheelchair every 2 weeks overnight with whatever godawful pile of crap the manufacturer shipped with your chair.

I bought this https://www.ebay.co.uk/itm/405108313343

If a chair is fully charged then after a few hours it will read around 13.2V give or take a little. After a week it may be at 13V approx. If it reads 12. anything at all it needs charging. Why does it drop? Batteries have an internal loss, called self discharge. And the chairs system has anything from 3 mA to maybe 15mA residual drain on top of this, 24/7 even when turned off. So if not using a chair DISCONNECT the battery. Or top off frequently like every 2 weeks max.

Any battery that is sat below its max fully charged voltage IS slowly sulfating and losing capacity long term. This is ONE of the things that kills batteries.
(Other things are higher average depth of discharge (so fit a big battery! Or charge intermittently as well as overnight for a few hours during the day)

If you want a easier long term storage solution hat YOU can choose the long term float voltage easily, do what I did and get one of these!
For under £10 you can just buy a cheap chinesium "power supply" that is 3V to about 36V. These are regulated and have just 1 adjustment knob! You must set this to the voltage you want. Then just plug it into the chair. Now the battery will be held FULL with almost no current and under 1 watt of AC power indefinitely. These are weedy. At 2A max. So are crap as a charger. But in the case of storage thats all we want!

So order one. https://www.ebay.co.uk/itm/405108313343
Whats bad about them? They fit crappy thin short AC cords!
They fit a long enough and equally thin DC cords. Its big enough for a weedy 2A supply electrically but a bit fragile physically!

Anyway, these are so cheap it doesent matter.

So FIT a AC plug to match your country (mine came with a terrible and illegal adapter! So I fitted a UK plug and a tiny 1A fuse.
I also fitted an XLR connector so I can charge a chair.
I CHECKED the voltage matched the displayed voltage and mine is pretty close. That doesent mean yours will be! So best to check before use.

[Burgerman]

First. Plug into chair, dont turn it on. READ the chairs battery voltage. Disconnect from chair.
Second. Turn on, adjust the voltage to what you want - probably 26.6 for long term indoor storage.
Third plug XLR into chair.
Leave for days, weeks, years as needed.
Once battery reaches the voltage set then current falls to almost xero, and drain on AC is around 1 Watt, (under 1 watt!) measured.

To TOP OFF a chair that is basically full, say a week on non use, set to 13.8 or 27.2V for 12 hours. Disconnect for a few hours.
Then set to 13.3V (ONE BATTERY!) or 26.6V for a powerchair with 2 batts in series, for LONG TERM storage...

DONT TRY TO CHARGE ANY BATTERY THAT ISNT ALMOST FULL WITH THIS! THATS NOT WHAT ITS FOR!

[Burgerman]

But the real reason you need one is for LONG TERM STORAGE!

Set to 13.3V or 26.6V and plug it into your chair. Best way to keep battery as close to new as possible for months to years.

Charging a chair (at any higher voltage) means some current long term and that causes grid corrosion, electrolyte losses etc and so gradual deterioration.
Not charging it means the chairs continued small drain even when off, combined with the battery slow internal self discharge garantees capacity loss over monhs to years.
Charging monthly or bi-weekly overnight causes less sulfation, but some battery wear/corrosion etc but is quite effective.

Long term float, means holding a battery at the 100% full point (so no sulfation can happen) but at a really low current so that negligable wear or corrosion happens. On most batteries at temperatures that WE are comfortable at, this happens to be around 13.3 volts. On AGM and gel.

So if its charged already, then set it 26.60V, connect it, and forget it!

[Burgerman]

Heres my salsa getting a bi-weekly (to a month max) 13.6V (27.2V) safe storage top up. A full day is OK for that if it hasnt been on or moved at this voltage. Up to a few days/a week max. Not very time sensitive. Will end up at 100% charged. Ignore the pile of junk on the seat.

13.8V (27.6) will also do this faster in a 12h to 24h session. And more time sensitive.

Once I know its full, I can then just leave it set to 13.3 (26.6) indefinitely. Long term. Safely. No danger of overcharge damage or sulfation. AGM or Gel, @ room temperature. Under 1W AC draw.

This thing is really bright clear red. Looks orange and very dull in pictures as its flashing/on/off at high frequency so doesent photograph well. Quite odd. Quite sensitive to set correct voltage. Once set its super stable over time, never changes.

[shirley_hkg]

It cannot control current.

Big initial Rush current when plug in ?

[Burgerman]

Its only 2A. It is controlled to limit to this 2A current automatically. Also protected against short and reverse current. So it just does 2A for a couple of mins then drops away to whatever the battery draws.

It isnt really meant as a charger. Just maintainer. It WOULD charge if you had a week to waste set to say 13.8V...

[scottnj@gmail.com]

That power supply looks like a good idea for a battery maintainer. The only thing that I would be worried about is someone else in my household accidentally knocking the dial up to full voltage and me not realizing it until the batteries are fried.

Do you know of any others that might need a screwdriver to adjust the potentiometer or something else that can't get accidentally changed?

[Burgerman]

No. But I do have a wall wart that is 1A and JUST HAPPENS to be the right voltage with a diode in series and no adjustment.
So its worth looking at a few. But no clue whare that came from.

[shirley_hkg]

or something else that can't get accidentally changed?

I found something similar. It has several charger modes(stops when full), and a POWER SUPPLY mode (CC /CV adjustable)

@£13.5

[LROBBINS]

A dab of goop or similar will "lock" a knob, yet can be easily removed with mild heat if you need to.

[Burgerman]

Or a quick dab with hot glue gun.

[slomobile]

Sounds good.

I wonder if there is a way to do the same thing by just regulating down the float voltage of whatever charger they happen to have.
I'm thinking an XLR to XLR adapter that goes between charger and chair, and can be removed to connect charger directly to chair when you need to fully charge in preparation for putting it in use again.
Using a chip like this https://www.ti.com/lit/ds/symlink/lm74930-q1.pdf and its bidirectional current control to burn off excess power in a resistor or other small load.

Not a lot of benefit over your method other than being automatic and easier to market. "Allows you to keep your battery charger connected indefinitely without harming your batteries"

[Burgerman]

Well if you want to complicate it you could just build a 4 stage charger. With a low V long term float as stage 4.
This relies on someone else to guess what the right settings are... Invariably these are always wrong.

Or a GOOD 3 stage that charged the 2nd stage and ended PROPERLY so that only 2 stages charged it to 100% and then only have a low long term float.
Harder to build as very battery/situation dependent for good settings.

But the main advantage of that tiny 1A or 2A ones I use is easy adjust, set whatever volage you want. And once the thing has been on charge a day or so the current is super low at the wall. I measure under 1W.

Of course many people never do any of this. And use stock mobility chargers in regular use. People also do not get the huge advantages of intermittently connecting to the charger for a while if get chance during the day. To lower average DoD levels. And run smaller batteries. Etc. So they get months instead of years usage.

*******
If you charge overnight CORRECTLY with correct complete charge etc, AND do daily opportunistic charging as you eat or check mail as well, and store at a nice low 26.6V continually when not in use then you SIGNIFICANTLY improve service life. BY 2 to 5 times, I have sets of very hard used batteries that were good after 7 years. By good I mean MEASURES not "still works"...

On the other hand, I originally used to charge ONLY overnight, and used a mobility charger, and did a lot of distance every day. And got 9 to 14 months at best per set of batteries. At which point they couldnt cope with my days typical use.

Why? All these things hurt lead batteries.
1. Too slow charging in cyclic use.
2. Incorrect stage 2 absorpion voltage.
3. STOPPING this stage 2 absorpion CV voltage too soon.
4. Not allowing enough time for the too high float level to top off the battery that is undercharged because of 3 above...
5. DEEP DISCHARGES! (murders batts fast). So do intermittent charges when you have an hour during the day. Several times daily if poss. Works best with 15A min to 50A charger. As it puts more back faster! But even a weedy 8A mobility charger helps a little.
6. HEAT cooler = longer life by a huge margin.
7. NOT 100% recharging, and doing so AS SOON AS POSSIBLE. Lead gel, AGM, and all lead based batteries hate not being 101% full!

So...
-USE QUALITY Battery! MK gel, Sonnenschien A500, Haze gel EV, Odyssey etc.
-USE LARGEST POSSIBLE CAPACITY THAT FITS!!!
-USE ANDERSON connection to charge so a faster charger can be used.
-USE A BIGGER Amp charger. 5A to 8A is not enough. 12 better (XLR) or bigger (Anderson 50) 15 to 50A.
-Set CORRECT charge voltage, 28.2V gel, 28.8V AGM, and set to end after 8 hours CV in cyclic use. Or when current stops dropping by 0.1A per hour. Or when 1/500thC to 1/1000thC occurs whichever happens first.
-Set 27.2V float and leave on for an extra half a day at least weekly.
-USE 26.6V float for long term storage AFTER a charge.

Do this above and your batts will last many years instead of 9 to 14 months.