Test battery for Ah after charge?

[briogio]

Is it possible to get an Ah number on a battery fresh off the charger?. I don't think the CA can give me a figure.

[Pure]

No it can't. But it can tell you how much you use before the LVC kicks in. Or you can hook it up to a string of light bulbs and monitor the usage with a Ah meter, or a watts up meter.

[dogman]

Yes no. A wattmeter, or an RC charger can tell you how many wh or mha went in. Chances are, you get to take close to that back out again, though a bms or balancer can burn off some of what went in.

I used to use an AC wattmeter to be sure a battery fully charged. When it had used a full kwh of 110v, I was sure the battery had fully charged from 100% discharged. If it took less, I'd have known something was fishy.

Mostly you just know you got x watthours last discharge to whatever you are considering the stopping point, so if you fully charged, you expect it to be the same this time. An RC charger does have the advantage of being able to show you the voltage of each cell, so you can see if any are undercharged, or even worse, charge way too fast which indicates low capacity.

[DAND214]

This where the CA SA comes in play.

Ca tells you what used and then you charge thru the CA shunt, if all is right you have 0 amps used.

I do that a lot, charge thru my CA SHUNT. I get almost a total rest on the AH reading.

Dan

[amberwolf]

That is also how I charge CrazyBike2's pack.

This can also be done thru the controller's shunt, but may require addition of wires from inside the controller to connect to the charger, and perhaps a switch to flip-flop the CA sense wires on the shunt.

[whatever]

I'm using an rc charger ( from hobby king: icharger 208b but there are cheaper ones should do same ) it shows how many ahr have been put into the battery during charging,
in fact I was quite surprised to find that i get about 10km for approx 3.5ahr put into the battery ( 48v, controller is 48v 18amp max).
The rc chargers are a very good investment for ebikers, so many things you can do with them.

[dogman]

Beats the green light on a charger, that indicates your battery is full. Or indicates your plug is broken, and your battery never charged.

A wattmeter tells you the power did flow, whether a dc wattmeter or just an AC one on the way into the charger. Either way, you know some wh went somewhere.

[amberwolf]

The rc chargers are a very good investment for ebikers, so many things you can do with them.

Just be careful and pick one that has been tested by others for accuracy/etc., if you intend to rely on it's numbers. I have a Venom here that is a rebranded E-station BC8, and it is not accurate at all, nor can you even simply add or subtract a set amount as it seems to depend on what it is doing and on what kind of pack as to *how* it is inaccurate. Cell and/or pack voltages read high one way, then low doing something else. Even though it's only a tenth of a volt or so, that adds up to notable difference from reality, and could result in overcharge or overdischarge depending on which way it swings in a particular operation. It also isn't even close to accurate on charging *or* discharging current, reading 6A+ when it is only 5A or less, 2.3A when it is really 1.8A, etc.

I don't know about any other chargers' accuracy, but those two would be ones to avoid if you need accuracy. It does work, but if you're trying to collect data for anything, it's not very useful. (except perhaps for the overall curves, generated via LogView on a PC).

[dogman]

Wow, that's pretty inaccurate all right. .1v off on a single cell even meets my slacker definition of out of balance.

Guess I got lucky with my turnigy cheapo chargers from HK. They agree with my cellog 8 at least, and agree with each other.

[amberwolf]

The problem I really have with it's inaccuracy is that it is not consistent; depending on what it is doing it will read differently. It is still better than not having one, for purposes like testing to get charge or discharge graphs, but I feel like I have to sit and watch it when it gets near the end of either.

Mostly, I just wanted to point out that not all of these things should be trusted to accurately charge your stuff. I suspect units like these to be a source of long-term pack damage from overcharge or overdischarge (if cycling for testing, for instance), that eventually result in some of the RC LiPo fires. With newer pack chemistries and better manufacturers, the packs can probably handle it, but with the older stuff that was less tolerant of any overcharge...well, you know.

Even the Battery Medics have been shown to be inconsistent. I suspect that part of the problem with some of these things is part tolerances not being tight enough, so too much variation from cell channel to cell channel, but that only accounts for units that have consistently inaccurate readings. For those like my Venom/E-station, it might also be in it's software design. I haven't investigated it, as there is little I could do to fix the problem either way. (no software skillz, and I have reached the point with eyes and hands that SMT work is almost beyond my abilities).