How to test amp hour

[Lil Giants]

Originally Posted by Espeefan

Sometimes, you might think the battery is the problem, when in fact a battery charger can be the problem instead. Cheap chargers sometimes false peak, before the pack has reached full capacity. It makes it look like the pack is bad, when it really isn't.

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?

[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?

[FlyingBeagle]

i agree with ESPEE fan for the most part. I have a good bit of experience with LIPO packs as most of my hobby time has been spent with Air Planes. I have several planes that run on LIPO packs and probably 25 packs of various size and voltages. LIPO's are finicky, and there are a lot of rules of thumb that you will hear from people some true, and some B.S. LIPO packs also vary widely in the quality between manufactureres and a lot of manufactures claims for capacity and C ratings are optimistic at best. As you would expect you usually get what you pay for although I have some cheap rhino packs from Hobby King that have out lasted and performed all the others in my collection.

I never discharge my packs below 3.3V per cell. Most flights I only take them down to about 3.6V per cell. My packs have all given me a good life cycle and I have only had one go bad so far and it was a cheap pack that never performed well in the first place.

I never cycle my packs unless I am trying to get one to balance as they do not have memory problems like other types of packs and they only have a certain number of cycles before they go bad. Why accelerate thier demise? Also if it is very far out of balance there is usually a bigger problem with the pack and I would be suspicious of it and probably just get rid of it. I may cycle it once to see if it is fixed, but if not it would be gone.

I always, balance charge them. I never charge them at more than 2C rate (4.4 amps for a 2200mah pack).

If they are going to be sitting for a while I store them at 3.6V~3.8V per cell. I never store them for more than a week fully charged.

Lipos do not like to be abused, and can become dangerous if they are not properly cared for. I had a pack with a bad cell go off in my hands as I was about to dispose of it because it would not balance. I was getting it out of the case and was going to puncture it in a fire pit with a spike when it just went off in my hands. 1 Minute earlier and it would have gone off in the storage case (ammo box) with all my other packs and likely would have burned my trailer and airplanes up with it. At best it would have coated all my hobby stuff with soot and smoke. A lipo that is more than a little puffed is dangerous. You should think about getting rid of it. It is not worth burning down your house or damaging a plane or the piece of equipment it is powering. Youtube has plenty of videos of LIPO fires and counting mine I have seen three in person and they are pretty wild.

Long story short, Joe you may be pushing your packs a little to far, but it does not sound like you are abusing them. Like anything if it is continually operated at its limits it will fail earlier. I imagine that your packs have quite a few cycles on them with the amount of work you have been doing. You may want to up your voltage cut off a little to help lengthen your pack life and always balance charge them.


Oh, and to the original question in the thread to test capacity (mah) you have to use the pack in its usual fashion and time the run time you are getting and see what the digital charger is putting back into it.

[Lil Giants]

Thanx for the reply Nathan. I should note that the Venom lipos started out working normally w/4600+ & starting on the charger above 12.5v. I think it was sometime after seeding when capacity started to drop, the packs would have been left fully charged for a month or longer. I can't remember when exactly they started to puff outward, but they have ballooned quite a lot now.

I was getting about 50mins run time with casual digging with the bucket, and around 40-45mins ripping - maxing the hyd press constantly.. about 10amp draw?

Cheaper pack? they run me about $65ea, what do the better ones cost? I have a 3300NiMH 7.2v paxk that's been in my bd trl 6 - 7yrs now, pretty good life span for a pack, though it's not a huge drain running the pump for less than 20s per load.

The original 3 lipos might be around 250 charges, I always let packs cool before charging, does that matter either way?

One of the three, I forgot the hoe on over night & drained the lipo well below, I tried the trick with the NiMH setting to get the volts back up & it worked with no issues for many recharges later. I charge my lipos in a large glass cookie jar with its metal lid, it all sits in front of me while I watch tv & surf the net.

Originally Posted by FlyingBeagle

If they are going to be sitting for a while I store them at 3.6V~3.8V per cell. I never store them for more than a week fully charged.

What's the reason for that?

A lipo that is more than a little puffed is dangerous. You should think about getting rid of it. It is not worth burning down your house or damaging a plane or the piece of equipment it is powering. Youtube has plenty of videos of LIPO fires and counting mine I have seen three in person and they are pretty wild.

Yes, I do see your point.. and my original 3 have ballooned out quite a bit!

Today I set my packs out in the yard & shot one of them with my .22 rifle about 5x to see what would happen.. maybe it would worth filming..


nothing happened!

I walked over to it carefully after 5mins of distant observation to only smell a sweet aroma coming from the pack & a faint hiss. So back to my rest & emptied my clip into the other two with no drama to be seen. Went into the house to put my gun away (took a couple mins) and came back out to clean up the mess with a shovel when all of the sudden the fireworks started with one of the last two shot! Sparks flying pretty good & then it burst into flames!!! Then other one was like a smoke bomb, big cloud of white smoke, that's all. Scraped them all up & dumped the remains in the burning barrel.

All 3 were fully charged prior to shooting at them, but they sat 4hrs on my cement step in -10C before I destroyed them.

You may want to up your voltage cut off a little to help lengthen your pack life and always balance charge them.

There's a noticable drop in pump speed a few mins before the cut-off kicks in, I'll change packs then & see what the voltage says. Might be a good thing to prolong lipo life. Thanx for the info FB.