How to test amp hour

[Themonty73]

Hi guys,

Is there any way of testing a battery's amp hour age as I have some battery's that are reading 12volt but I don't think they have enough oomph in them?

Many thanks

[Espeefan]

I could think of a few different ways to see what your battery's max capacity is.

You could fully deplete the battery (almost dead) and put it on a charger to see how long it takes to charge up, at the given current rate you set. If you can't set the charge current, then you'll have to see what your charger puts out, at it's fixed rate, and do the math. For example, a charger that puts out 5 amps, for 30 mins, will have put about 2500 mili-amps, or 2.5 amp hours of charge back into the battery pack. If your pack is rated for 5000 mili-amps, or 5 amp hours of capacity, and it only wants to take half that, from an almost fully depleted state, then it's lost a lot of it's capacity.

Some fancy chargers will actually display the amount of charge a pack has taken, in mili-amps. That's the easiest way to know how healthy your pack is.

Still not sure? Take the pack, fresh off the charger, and hook it to a load that you can measure the current with. For example, hook it to a motor and measure the current draw of the motor. A motor that draws 5 amps, continuous, under load, will be your known value. If your battery pack can continuously support that 5 amp draw for 30 mins, then you know it's max capacity is only 2500 mili-amps, or 2.5 amp hours.

Another easy way, but not cheap way, to know what your battery's condition is, would be to get a current monitor gauge hooked up in series with it. Monitor the current draw, of the load that way, and see how long the pack lasts. Then it's simple math to solve for the battery capacity. Here's the Watt meter I have. http://www3.towerhobbies.com/cgi-bin...&I=LXLMV0&P=ML You can do the same thing with a digital multi-meter, wired in series with the load, or current draw.

Or, if your battery charger has a discharge feature, you can run the battery down using the charger, and set the discharge current rate. How long it takes to discharge will tell you the capacity too.

If your batteries are old, and you haven't cycled them much, chances are they have lost a lot of capacity from just sitting around. You might not be able to bring them back to life. Even a battery that is heathy, and is cycled on a regular basis, will continue to loose capacity, the more it is used. A little at a time, but eventually it will suffer a noticable loss.

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.

Hope this helps

[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.

[Themonty73]

Hi guys,

Thank you for all your replys, It looks like the nimh battery's are on there way out not sure how old they are but will source a new ones from some where.

Thank you all again

[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.

[Espeefan]

Joe, your LiPo packs should surrive a long time, with such low current draw. 10 amps is nothing, compared to what sort of loads battery packs likes these work under, on monster truck, buggy, or other racing applications. It's not uncommon for these packs to deal with 30 or 40 amp continuous loads, and surges past 100 amps. Your excavator should be a walk in the park for them.

As far as charging, it's always best to let a pack cool, before you charge it, but as long as the pack is not super hot, it should be fine. Also, LiPo packs do not develope memories, so you can charge them anytime, even if not fully discharged. Also, the more I've read, the more I'm told you can charge a LiPo pack as many times as you like, in one day, with no ill effects, so given all that, I can only assume the life of your packs was decreased just from normal wear and tear.

As for the recommended storage voltage, I have no idea why they say to do it with 50% of the battery's capacity.

[FlyingBeagle]

Joe,
I dont know why the storage voltage matterts so much either, It may be a safety thing as a fully charged pack has more energy to disperse in a failure than a partially discharged pack (i.e. more fire and smoke). I can tell you that it has been my experience that the batteries for my micro heli and plane have not gone bad as quickly since I began storing them properly.


Regarding your charging jar, that will probably work well to contain the heat and fire but I wouldnt put the lid on tight for fear it could explode in a battery failure. As you witnessed the packs put off a lot of hissing and smoke and can create a good bit of pressure in an enclosed space. I would hate for the jar to explode and pepper you with glass. I never charge batteries in my house as I would hate to have all of the smoke inside if there was as failure.

-10 C wow, that is COLD!!! I would think that you would have gotten a much better show if they had been room temperature. I know a cold LIPO pack does not perform nearly as well as a warm one. -10 C I am amazed, I never felt anything near that cold.

Here a couple of links to some fairly useful pages discussing battery care. I see thes pages referenced quite a bit on the airplane forums.


http://www.hangtimes.com/redsbatteryclinic.html

https://sites.google.com/site/tjingu...po-terminology

[Lil Giants]

Thanx again for the informational replies fellas. And what a couple of great links for battery info of all types FB, you should post them in the Favorite Links thread.

oh & no doubt the results of destroying the lipos might have been vastly different if I hadn't gotten distracted with a ringing phone & forgotten the packs outside on the cold step, which is why I made mention of it & then saw not much excitement.

-10C can be a shocker when the temp might have been +20C the day before, but really it's quite mild compared to -40C = -40F that we do see sometimes during the winter. It hasn't gotten remotely close to that this yr yet.. usely January hi-lights.

[doodlebug]

I'll second the cold up there! Going back up Sunday for more hay.
Thanks for more battery info. What a great. Bunch Of people here!
Cheer's, Neil.