How to test amp hour

[Espeefan]

Originally Posted by Lil Giants

I have these Venom 4s 25C (charge rate 1C) 5000mah lipos for my JD850. The 1st three I had last yr were cycled nearly everyday (all three) & were balanced charged everytime (charger set to 5A, but usually showed 3.3A or less). By summertime I wasn't getting much runtime from them & charger only showed 3 to 3500mA & the voltage @start of charging was over 14v. I thought something was ary with my lipo cut off of the esc I was using in the model.

I got three new Venom lipos mid October, the same everything as the old ones, they are working like they should in the model, draining down to 12.5+v & using up 4600 to 4850ma every use. The 3 older lipos have gotten worse & are now down to 2600ma per use and upwards of 15v at the start of charging.

Visual comparison of the old vs new, the older 3 lipos have expanded outward quite a bit.

Since mid October I have been just "charging" all packs and now having six lipos, the new ones are not getting cycled as fast as the old ones were last yr. And also I'm not digging anywhere near as hard as this time last yr, so the lipos aren't being drained as quick either. Last yr when I switched out a lipo, the lipo was warm, but now that isn't happening with either of them.

Is it better to charge lipos vs balance charge? Or just balance charge on occasion?

Why did my original 3 lipos go bad so quickly? What do you Nathan (or anyone?) suggest that I should have done differently to keep them in optium working form longer?

Joe, LiPos are something I don't fully understand 100% yet, but from the reading I have done on the subject, it sounds to me like you were doing everything right, in maintaining them. Any LiPo pack should never be discharged below 3 volts per cell, so you having 12.5 volts plus, left in a 4S pack, after depleting it, sounds safe. The 1C charge rating, with a 5000 mili-amp pack would be a max of a 5 amp charge, again exactly what you were doing. The discharge C rating, of 25, means your packs should handle 125 amp current draw, which I highly doubt you came close to with your excavator! Any idea what your excavator does draw, continuous?

So why the shortened battery life, I'm not sure. I've had some Venom battery packs, although never their LiPos. My experience with Venom battery packs is that they loose their capacity very quickly. They are a cheaper grade of battery pack, in my opinion. I ran some 5000 mili-amp 7.2 volt NiMh packs, from Venom, and even brand new, they never took a full 5000 mili-amp charge. I just don't trust their packs to be of good quality. Though your second set of packs is doing fine. Maybe something changed, with the construction of the packs since then, and they have gotten better?

The biggest things that kill battery packs is heat (excessive current draw), overly discharging them, or over charging them. I hear of people using a balancer on their LiPo packs only once in a while, while charging. Some only every 10th time. Ideally, using a balancer everytime is the best for keeping your packs healthy, but I think some would say that is overkill. The whole point of balancing a pack is to be sure that each cell is properly charged, and not over charged. Likewise, you don't want one cell to not have enough of a charge either, because the next time you run the pack down, that cell could be discharged beyond what is safe, while the others still have plenty of capacity left in them.

I've heard people recommend you should not discharge any LiPo pack beyond 80% of it's total capacity. So a 5000 mili-amp pack shouldn't be left with less then 1,000 mili-amps of capacity in it, when you are done using it. I'm not really sure how you would know this, other then by running a timer, and guessing at the average continuous current draw of the load that is being run by the pack. Once you put the battery back on the charger, you could see what it takes, but then not all 5000 mili-amp packs are going to have a true 5000 mili-amps of capacity either. Anyway, isn't the whole point of running a voltage cut-off, to protect your pack?

Tough to say Joe. If you are getting longer life out of your packs now, then you must be doing things right. I could only assume the shorter life was because you were cycling the packs more often, running them harder, or because the quality of the pack was simply poorer. It really doesn't sound like you were abusing them. LiPos do have a life span too. Something 300 to 400 cycles? If you charged a pack once every day, for a year, then maybe it's just normal wear and tear. Some people on the internet say they have gotten 1,000 charge cycles off their LiPos, so who knows?