Charger voltage testing

[biscuit]

Is it possible to find out what my "generic" chargers are doing? I'm thinking they are killing my batteries. My first wheelchair came with the old 3A charger that came standard with the Vienna chair. Mako Mobility up the road fitted new batteries when I got the chair, and those batteries lasted for about a year very reliably before dying. I very much doubt that those were particularly good quality batteries. That charger fell apart and since then I've been using other smart chargers . I always lost a light (and speed) before I left the carpark. I got a new Vienna & charger lately which does no better. I think the charger might not be the right voltage.

I've got one of those 2 pound multimeters but I don't think it's really suitable for testing mobility charger voltage.

[Burgerman]

Those really cheap meters are frequently miles out. So I would see if you can find, beg, borrow a fluke, agilent, or at least something a bit less chinese £2...

But its not really about voltage. Well it is, but its also about making sure that they are FULLY 105% charged.

If you have AGM batteries, then the charge voltage must be 14.4 to 14.6V.
If they are GEL batteries the charge voltage should be 13.9 to 14.1V.
The AMPS dont much matter. Although more is generally better. Saves a little time.

As you begin to charge, the voltage should slowly increase to this level over a few hours, unless its already pretty full. And it should sit there solidly at this voltage for around 8 hours or a little more. The green light should then come after around 12 hours total. At this point they are charged. And the charger does not need to do anything else.

But some charger will now switch to float. So now the voltage drops to 13.5V indefinitely. If your charger does NOT take 10 to 12 hours to go green, then this means its far from fully charged. It means that this float stage (on green) needs to stay connected for another 6 to 12 hours or longer. And only then is the battery fully charged.

Obviously if you have 2 batteries the volts are double all the figures above.

This shows what will happen if your charger is working properly. Note that it always takes 7 to 12 hours on the absorption stage. At your voltage.

[Burgerman]

You will need to measure battery volts as they are charging. And keep checking for many hours...
Easy things to check.
How long does it take before you get a green? Less that say 8 to 10 hours? Then it MUST also have a 3rd stage. So check that the volts are around 13.5 or 27V total, a few hours after the green. And then 6 hours after the green. If it is thats good. But it means the charger will take 24 hours for a complete charge.

A complete charge is essential or the batteries will have a short service life and range will get worse and worse fast! Its the final 1% thats important. Or some lead sulfate remains on the battery plates. And it builds up every charge. So after 10 charges, thats 10% of the capacity lost... And if not FULLY charged soon after discharge, that sulfate layer turn to large permanant crystals and cant ever be returned to the acid where it came from.

But. Cheap batteries. Over discharge level. Bad chargers. ALL contribute to the problem and are a perfect storm..

[biscuit]

My Shoprider lives on charge for days at a time. My indoor wheelchair, I don't care about its battery, I, but it gets a 24 hour or more charge about once a week. They get a lot more charging than they ever did with the old Shoprider charger. I'd hoped that it was a matter of charging for longer, but I don't think it is.

[Burgerman]

Charging for long enough depends on the chargers having a FLOAT stage. At least if they say "charged" in under 10 hours or so. Many do not...
And also depends on the charger charging at the correct voltage, for long enough before going to float...
It also depends on both batteries never being discharged too deeply. Cheaper batteries can only give a few 10s of really deep cycles. Which is why I use MK Gel, or Odyssey.
Also the battery fitted by design may be inadequate. Meaning average daily discharge level is too high by design.
Hills kill off batteries.
Cold means much less capacity.
Charging at too high voltage, by just a few 10ths of a volt can reduce life by 60%... At least on gel.
And cheap batteries chinese AGMs, are crap to begin with!

So its seldom one cause.

[biscuit]

Ok, I'll be aware that using the chair in winter isn't going to show is batteries at their best whatever I do. My light in both chargers go green quickly, like 5 minutes or less.

A pl8, can it charge my Vienna? it would need an XLR output because my batteries live in a box with an xlr charging port and they'd be a big pita to remove every day.

[LROBBINS]

You don't need a PL8 (plus power supply) to charge lead batteries. The ZXD charger available via the kind offices of of Shirley_hkg can readily be set up to do exactly the charge curve John has described, and though capable of giving up to 50 Amps, if you set it to max out at 12 A it can be connected by an XLR plug. The ZXD is available in several states: (1) already modified to be a variable voltage supply/3-stage charger but in its original case, (2) modified and shipped with the pieces to put it in a fancier aluminum case (some work needed - see the long thread about the ZXD), or (3) already in the fancy case. Stock fans are pretty noisy, but for not too much money (and again, some work) they can be replaced with low-noise, thermostatically controlled fans that make it very quiet. The later, if you switch to LiFePO4 it can serve as a rock steady power supply for a PL8 (or whatever's available and best then).

[Cornbread]

if you know someone with a quality meter, you can ask them to check yours against it. Of course owning a good one is better. But use what you got also applies. I've got a fluke that I checked my box store specials against. Some were waaaay off and trashed, while others were surprisingly on point. Perfectly fine for checking voltage. Some read a bit high, some low, as long as they were consistent then I kept them. They are my loaners, so if they disappear or get damaged no real loss.

[Burgerman]

If your charger shows green after 5 mins then throw it away!

[biscuit]

If I remain silent on this thread from this point, it is because as usual every single word of every single response is giving me a lot to think about - for example finding out what a fluke is, which I suppose everyone else here knows, but not me... and Shirley's machine, I haven't started reading that thread at all, it was information overload for me. Shirley when I have a clue what I'm talking about, I will pm you. Or maybe before that point
It sounds like my chargers are even worse than I'd suspected.

[stevelawiw]

I know what you mean. There is a crazy amount of information on this site, all good stuff that will improve your life, but taking it all in

[Burgerman]

Fluke = a brand of multimeter and test equipment.

Not usually cheap, but they make multimeters from around 70 uk pounds that you can rely on to be at least somewhere close to accurate. Up to many hundreds of pounds if you know why you need that level of complexity. This is way more than you need. But at least I know its accurate as it has a recent fluke calibration certifcate.

Heres mine above in the pic.

Heres the cheapest fluke test meter.
https://www.markhennessy.co.uk/budget_m ... ke_101.htm

Doesent have to be fluke to be accurate. They are designed to last, be safe at high voltages, be reparable, good backup etc. Work tools. A set of leads for a fluke can be 50 pounds... As I said more than you will need.

[biscuit]

BM do you mean that I can't test my charger directly, the only way to do it is to test my batteries while the charge is in progress, to see what effect it's having?

Sorry if that's a half-witted question. I need things spelled out or I can't understand them, usually.

[LROBBINS]

I'll answer for John. Most chargers will not output anything unless a battery is connected. To see its behavior - initial rising voltage at constant current, longer term constant voltage with falling current, steady lower float voltage - you need to measure the voltage throughout the cycle, or at least monitor it periodically if not continuously.

[Burgerman]

As lenny said above. The answer to your question is yes. And its very time consuming.

I do a lot of such measurement of things with solar systems, batteries, simple electronics, or figuring out why my van eats its battery for e.g.
So I use that fancy fluke meter above. Because it can be connected and set to log the voltage over time. And display a graph of voltage or current, or frequency or whatever over any time period. And I do not need to watch over it. It keeps all the data for me. Its really useful, but stupidly expensive.

Right now its monitoring the temperature of my bedrooms upstairs over a week. So I can correctly set the radiator thermostat to 65F and will do so in every room seperately.

[Arima]

do you mean that I can't test my charger directly, the only way to do it is to test my batteries while the charge is in progress, to see what effect it's having?

Sorry if that's a half-witted question. I need things spelled out or I can't understand them, usually.

That is the kind of question I would ask myself. Cause I want to know if my charger is doing it's job. It's a good question...turn it into a number question. Something like... Is my charger outputting (when it is connected to a battery) the correct number of volts and amps over a period of time. As in the graph below...which funnily has no numbers on it. The numbers hurt my head but it is the only way.

I've got one of those 2 pound multimeters but I don't think it's really suitable for testing mobility charger voltage.

Can you make a graph of your charger at work on your chair? I need to do this myself. I like the graphing function on the Fluke brand multimeter...there have got to be others for less money.

[Burgerman]

The PL8 charger many here have does the same graph as it charged onto your PC.

Heres my last ones
One is volts. and one is amps, showing the current fall over a very long time. Thats how long it really takes. Cannot be made faster.

This is a real graph, accurate to several decimal places..
I was charging a very large single battery. This was supposed to charge at 14.70V. The graph shows the charger charge at max power until it reaches the choosen voltage. And then it holds the battery at exactly this same 14.70V.
Note that this isnt yet complete, and that it took 9.5 hours. SO FAR!

VOLTAGE GRAPH

And this shows the MAX charge Amps, being applied, until it reaches the same 14.7V (ABOVE GRAPH) and then it gradually drops, and drops as the battery accepts the charge. Note that this isnt yet complete, and that it took 9.5 hours. SO FAR!

AMPS GRAPH

[Burgerman]

And THIS is the same pl8 charger, NOT charging. It is being used to MONITOR voltage only. In this case not by me,

The battery is being charged on scootermans chair, from memory, with a invacare upright style mobility charger...

516e898945556_flexel-scooter-charger-24v8a.jpg (16.72 KiB) Viewed 10479 times

Notice that its a complete mess, all over the place, wrong voltages, and it stops way too soon. Unfortunately, this is all too common.
Maybe you can see why I like the PL8! It should have looked the same as the first black graph above. If it was charging properly. Unfortunately non do!

Note that the scribble all over it was scootermans attempt to figure out what the hell was going on. This graph SHOULD have looked like the black ones above! Mobility chargers are generally junk. This was an invacare one. And it will destroy batteries. Note that it only "charged" at the wrong decreasing voltage, for 4 hours. Then appears to go to a too high 13.8 (double this as its 2 batts) float. They dont care. Its all £££$$$...

[Burgerman]

Heres another PL8 charge on a wheelchair.

Here I am charging a Salsa Wheelchair with gel battery, correct voltage is 14.1 or rather 28.20V as theres 2 batteries in series. Notice that its taking a LONG time. And this is charging at 12A. Thats higher than a typical mobility charger. So its faster!

VOLTS shown here. It was instructed by me to charge at 28.20V.
And initially you see the battery voltage rising, and then it sits at the correct voltage. For a very long time! And is still charging here!

VOLTS

And again, this shows the initial max power of the charger pushing the volts up to 28.20V. And then it shows the natural absorption of the battery as the current (Amps) naturally falls. When it falls no more, or after around 8 to 10 hours at the high voltage point, then charge is complete. Float isnt required.

You CANNOT charge faster. Here its not finished. It ended after around 14 hours.

AMPS. Around 4 or 5 hours left to go!!!

[shirley_hkg]

Why it drops volt , instead of CV, during absorption, and jumps to float immediately afterwards.

[Burgerman]

You mean scootermans mobility charger (yellow graph) ???

Because it is a invacare mobility charger. Like all the mobility chargers that I tested they are usually hopeless. And all are different. Scooterman tested his, just to see how bad! If you look, the only part that seems OK is the last bit. Is that meant to be float? Its at a too high 27.75V? And its going to need 16 hours of that! Since it only charged for 3.8 hours at the not very CV!!! At ever decreasing wavy voltage... Rubbish!!! That charger will result in rapid sulfation and short range. Thats why I dont use mobility chargers. They are mostly junk.

I charge using a bench power supply, or the PL8. Because I can choose the right settings, and they actually do as I set!

[shirley_hkg]

I still have 3 of them.

Each costs more than my PL8+psu together.

[Burgerman]

For those that have no idea what we are talking about!
The PL8. Is a very advanced charger. That I had a hand in making so useful!

Fully programmable, can charge any battery type, chemistry, lithium all types, lead, nickel metal, nicad, etc. And at any voltages, amps up to 40, and graph and display results. Also can discharge and measure battery performance, as well as monitor other chargers...

From left to right.

1. Silver thing, is a 0 to 50A and 0 to 60V power supply. In this case its being used to power the PL8. Want one? See shirley! It also can charge a lead battery properly WITHOUT a PL8.

2. The PL8. The red and black thing in the middle! It can charge anything. Any chemistry. And measure and display whats going on. Propely. Very user configurable. Overkill for lead. But it makes graphs! Tests capacity etc. And is very accurate. Essential for lithium conversions.

3. A cheap fluke test meter. Yellow thing... Not needed.

[Burgerman]

Biscuit never expected it to get this complicated. And now has smoke coming out.

Cant help it. Batteries and carging are not simple one line answers. And there are detail that really matter. Unless you want the wrong answer. Sorry!

Keep asking (dumb?) questions. Thats how you learn. People that know dont remember how hard it was when you didnt...

[biscuit]

Lol yes my brain is frying. I'm gonna ask Shirley for one of the all singing all dancing silver things, if he's in a position to supply one. But I will only have money for one in April so meanwhile I'll try measuring.

I see that my light isn't the thing that goes for <5mins, it's the fan actually that does that. My charging day usually ends with Stage 1 and I don't really feel like staying up all night to measure that silly machine so it won't be immediate. However if I get a ZXD2400, measuring the other chargers' performance will only be for interest.

[shirley_hkg]

For those that have no idea what we are talking about!
The PL8. Is a very advanced charger. That I had a hand in making so useful! ... Not needed.

PL8 would still be useless to us wheelchair bounded, if it had not been unleashed from all those FMA limitations by YOU.

Hats off to you, BM.

[Burgerman]

About a year of emails and testing and persuading a very stuborn bunch of programmers and beta testers!

Your invacare style chargers may be different. Every one I ever measured or monitored did something completely different. Some were more "ok" than scootermans one... None were great.

[Arima]

I don't really feel like staying up all night to measure that silly machine

Probably the reason everyone doesn't graph the charging cycle. Thinking about the logging multimeter I'm not sure how it can measure voltage, current and temp while keeping timing. When I use cheap old meter I need to physically switch between volts and amps. This can go in the dumb idea box unless someone else knows how to capture the data and save it cheaply.

[Burgerman]

It only measure volts. Or amps. You only need measure Volts for this though. As a quick guide.

I just use my accurate clamp meter thats accurate to 1mA to measure Amps. Every now and again. To check its still dropping away. I use the small yellow one here. https://www.youtube.com/watch?v=1sq2WRGPABw Or this does the same thing for 1/5th the price. https://www.youtube.com/watch?v=r7QjTEE2Sn0

Same with the PL8 if MONITORING another charger. Volts only.

If you CHARGE with the PL8 it automatically graphs both Amps and Volts as you watch...

[Arima]

Okay just measure and log volts during the day while on basic 8amp charger is what I understand. Just looking for the curve to go up to something near 24volts correct? Measure at the battery post or ??? If I need to do this to each battery separately that needs a bit more effort. Probably good to run down the previous charge so there is work to be done. Almost sounds like a plan:)

I won't see a smooth curve...mine will be more like scootermans? That curve goes the wrong way I think.