Thinking out loud

[martin007]

Suppose there are two standard powerchairs.

Powerchair number 1 has AMG batteries.
Powerchair number 2 has GEL batteries.

The gel batteries are charged at 28.2 V.
The AGM batteries are charged at 28.8 V.

The charge level indicator that the control knobs have has no way of finding out which batteries it mounts.

With what type of batteries does the estimator think of the level of charge it is?

[biscuit]

Is this question more technical than it looks?

It's easy to say that joystick battery lights are a guess.

[Burgerman]

The voltage of a battery in use has nothing much to do with the voltage you charge it at. Which is typically around 12. something volts as soon as you move 10 feet.


Does the powerchair understand the difference between AGM and GEL?
Both have quite similar STATE OF CHARGE voltages. Within a tenth of a volt. But thats not important. In use the voltage jumps up and down by 2 or 3 volts over a few minutes depending on load. And hen it takes a full day to "normalise" where the voltage then relates to state of charge. So the battery meter is at best a guesstimate. Not remotely meaningful.

Is this question more technical than it looks?

You have no idea! Its not difficult it is impossible.

[shirley_hkg]

It's easy to say that joystick battery lights are a guess.

You are right . Since AGM and GEL had different discharge platforms , you could program the controller to tell you much or less the same level of guess.

You can try it with your ZXD2400 adjustable psu.

[Burgerman]

The problem is that the battery meter checks voltage when the joystick is central. No load.

And this can read ANYTHING depending on the last 12 hours or more usage.

For e.g If I cruise along at 4 or 5mph for 10 mins then I may take just 10A out for 10 mins. The battery voltage remains high. Say 12.7V.
If instead I take the same omount of Ah out going up a hill in 1 minute then the current is 10x higher. This drops the battery voltage down to maybe 12.4V. It revovers IF UNUSED to the 13V point over the next 12 to 24 hours. Quickly to begin with. Then ever more slowly.

In the first case the meter will read as if the battery is full.
In the 2nd case the meter will read as if the battery is partly discharged. At forst. Then over time it will read higher and higher.
In both cases it is wrong. In different directions...
By a much greater margin than the tiny difference between gel and AGM. In fact the important differences are IMPEDANCE and PEUKERT and discharge or charge history rather than difference between AGM and Gel.

[slomobile]

You can try it with your ZXD2400 adjustable psu

I think Shirley was saying hook up a variable power supply to the chair instead of batteries. Don't drive the chair, but turn the power supply voltage up and down to determine the exact voltage that each level bar on the gauge comes on and off.

How do we buy one of them from you? In my case I'm in US.

[LROBBINS]

No, you buy it from Shirley. PM him to get current price and availability.

[martin007]

You can try it with your ZXD2400 adjustable psu

I think Shirley was saying hook up a variable power supply to the chair instead of batteries. Don't drive the chair, but turn the power supply voltage up and down to determine the exact voltage that each level bar on the gauge comes on and off.

How do we buy one of them from you? In my case I'm in US.

What you are saying is not viable.
I don't have to buy anything.
I have bought 2 chargers from Shirley.

[slomobile]

Sorry if I was confusing. I wanted to buy a charger from Shirley, not you. I just didn't know if there was a digital storefront or something I was supposed to go to. This thread gave me ideas for a testing a bunch of stuff, including noting the exact voltage that each bar on the joystick represents.

*note- American apologizing. May never happen again.

[Burgerman]

Most modern joysticks dont work directly on voltage. They try to estimate the past usage/peukert and voltage depression and the voltage loss under load of the cables seperately. They then have some kind of map that means the current voltage will give you a different numbers of bars regardless of voltage depending on usage history and whatever the programmer thouht was a good idea. And it seems that he was an optimist.

XXDs can be had from shirley, PM him. In the same way I just bought another PL8 charger.