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albert465

How long should I charge my battery???

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Hi,

I've just built my first RC a re-re grasshopper and got the battery and charger thrown in from the shop. Its a 2000mAh battery and a Ansmann AC30 charger just wondering how long I should charge the battery for on trickle and also will the 30 min fast charge fully charge a 2000mAh battery.

John.

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There's a formula for working out how long it should take to fast charge a battery:

( Capacity (mAh) / Charge Rate (mA) ) x (efficiency constant) = time (H)

The efficiency coefficient is usually about 1.4 for fast charging, but will vary a bit from battery to battery. The AC30 charges at about 3A or 3000mA on fast charge, and your battery is 2000mAh. So using the above formula...

2000 / 3000 * 1.4 = about 56 minutes.

I am not sure what the trickle charge rate is from that charger, but it's usually around 0.1A. At that rate it's going to take about 24 hours to charge the pack.

When fast charging the pack, the battery will start to get very warm when it is nearing its full charge.

I'd suggest putting the pack through two 30min charges, and see when the battery starts to get very warm during the second charge. <edit> and immediately stop charging when it gets very warm. Note the time elapsed in the second charge so you can set the correct charge time next time.</edit>

- James

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Hi John,

2000mah means 2000 milli amp hours which is 2 amp hours. so if you charged at 2 amps it would take 1 hour, at 1 amp would  2 hours , at 4 amps would take 1/2 hour etc.

with a new pack its recommended to trickle charge for the first charge, this allows the voltage of the individual cells in the pack to stabilise ( if there is any individual instability) and the pack to 'bed in'

on the charger(or in the supplied document) it will say the trickle charge rate. for example 100ma which is 100 milli amp i.e. 0.1 Amps , at this rate your pack will take 2000mah / 100ma = 20 hours minimum to charge. i say minimum because the losses at such a charge rate are significant. if this is the trickle charge rate leave it for 24hours, any longer will do no harm at such a low rate, excess charge will be dissipated as heat.

with your charger there is no readout of how much charge you are putting in to the pack. i am not familiar with the charger you have, i have just read that the fast charge is timed limited to 30mins , then it auto switches to trickle charge. some websites say it's  fast rate is 2 - 3A. i dont know how the charger determines a full charge? some chargers use heat/delta peak etc but are not senstive to such for the first xx mins. Also various websites recommend this charger for packs up to 1700mah only.

i would NOT recommend fast charging for 30mins then fast charging again for a full 30mins at all. Never fast charge a fully charged pack whatever the chemistry. the method james suggests is possible but do not leave unattended on the 2nd charge!!!!!

 personally i use a Schulze 330d charger which has an LCD display of how much charge has gone in ( and also how much out on its discharge setting). i have been using it for years for electric flight wilth nicd's, nimh's and lithium polymer batteries. its ultra reliable. tough as boots and fully  upgradeable if need be.  for example if i were to charge your pack with it, i'd set it a say 2amps  ( its selectable between 0.1amps and 5.5amps) and it would take 1 hour to charge, it automatically stops when its full and displays the exact amount of charge 'put in' , this is helpfull because it allows you to monitor the packs well being, for example if id run it to 'empty' and it only put say 1346mah back in id know the pack was dying.

it also allows you to select 'auto charge' and it will ramp the current up to whatever it detects the cells and charge leads can handle, and tail the charge off once the pack is nearly full. it also has multiple charge/discharge cycle programs which are good for wakeing a pack up this hasn't been used for a while, or for prepareing a pack for storage. (storeing a pack when full will cause very significant loss of capacity holding ability)

 wah! abit long winded, but its all usefull  [;)]

Have fun!!

Alex

 

 

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Just clarified my post above. [;)]

The Ansmann charger only has a fast charge timer, it doesn't use peak detection it appears.

I use a Duratrax Ice charger, it's superb.

And regarding battery storage - It's best to store NiCD nearly empty, but from what I hear it's best to store a NiMh with about half charge.

Note about discharging the battery - when the car starts to slow down at the end of the battery charge, that's the best time to stop. If you keep using the pack from that point on, you could over-discharge one of the cells and cause it to reverse.

- James

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If it helps, the AC30 is rated on the box to fully charge a 1400/1500 battery in 30 minutes.  So rule of thumb is much simpler - if it's 10 minutes for 500ma, 20 minutes for 1000ma and 30 minutes for 1500ma - give it about 40 to 45 minutes and you should be spot on.

Remember, if you're giving it two blasts on the fast charge, always do the shorter charge first as that way you're not likely to give it a full hour if you get distracted.

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I've got 4 nicads that I think have had cells gone into reverse.  It was a couple of years ago, when I was running a boat and wanted to squeeze more runtime out of it.  Big mistake.  I've been trying to get them to hold/take a charge on and off for a while now.  My friend just got an old Falcon, so I've been trying to get those old packs charged up.  I think I might have had some success with one 1800mah pack.  I let it charge on a 400mah "wall wart" charger until it felt very slightly warm, then put some charge into it with an older timer charger.  The charger doesn't have any rate selector, just a meter that seems to show a varying charge rate depending on how full the pack is.  Anyway, I charged it that way until it was pretty warm - about as warm as pack is after a good run in the car.  I immediately took it outside and managed to get 10+ min. of runtime.  I let it cool off completely then charged it with the timer charger until it was pretty warm, but warmer this time.  I took it out the next day, but the charge seemed to drop off pretty quickly - 1 or 2 min.?  Is it possible that the pack isn't holding it's charge overnight?  If a cell has reversed is it possible to coax the pack back to life without a complicated/expensive electronic charger?

 I also have a question regarding how my friend should charge his new 3300mah nimh pack.  He only has a 500mah plug in "wall wart" type charger.  Can he charge the pack using this type, and the old "stop when it's warm" technique?  Is 500mah too high of rate for the first few charges?  Once charged, can he run the pack normally in the car, or does he have to drain it gently?

Thanks alot,

Rob

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The most common reason for damaged batteries is overcharging (The next most common is probably over-discharging). For this reason, I recommend investing in a decent delta peak charger if you're going to use decent batteries and want to remove the guesswork from charging, and want to charge at a rate over half the capacity of the battery.

Modern cells shouldn't really need trickle charging, fast charging them is fine - as long as you are careful not to overcharge. NiMH cells usually come with some charge in them.

For that old NiCd pack, I would try cycling the pack a couple of times, fast charging it at 3A or 4A on a decent charger and see how it goes.

A NiCd pack that's left charged will slowly lose its charge, but not as rapidly as you describe. It normally takes a couple of months to go that flat. I suspect one or more cells in that pack is probably shorted due to material buildup inside the battery. Zapping the pack may help, which is putting a large current through the pack for a short time, but if the pack is self discharging it's probably a lost cause.

If you suspect there are problems with individual cells in a stick pack, then there isn't much else you can do without dismantling the pack.

- James

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James,

Thanks for the help.

I charged up the old nicad again today with timer charger until hot, and managed to get a good 10 min. or so out of it, so it seems that they might usable, but only when pretty fresh off the charger.

I myself have a GWS peak charger that seems to do the trick for my nimh 3300 pack.

My friend was looking for a cheap peak charger to go with the 3300 nimh that he's buying(tonight actually), but all of the basic peak auto chargers were for nicads.  Do they make a basic type charger that works for nimh?  He wants to charge it up tonight, but as I said right now he's only got the wall block.  I told him I thought it was safe to use it, as long as he keeps an eye on the temp.  Is it ok to charge nimh with those?

Thanks again,

Rob

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Rob,

 I'm currently looking for a new charger.  For me, it is between the ProPeak 2500 and the Ansmann ACX1.  Both are around £30, and both will charge Ni-MH from 12 and 240 volt sources.  The main difference appears to be that the 2500 has a 1 hour shutoff (actually 66 mins I have been told) and the ACX 1 has a 90 min shutoff!

 Andy

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If the propeak is a 2.5amp (2500 suggests it might be) you'll find a 1 hour cut off means it may cut on a 3000 battery before it peaks.

The ACX1 with the 90 minute cut off means it's OK to charge up to approx 3700 nimh (despite what it says on the box) we've successfully tested it up to 3700 and it peaks before 90 minutes but don't have any packs above this to charge...

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Just checked, and the Propeak is 3.5A charge rate.  It would be interesting to know if one or the other is actually better!!!!

Andy

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While you technically can use a NiCD fast charger to fast charge a NiMH battery, since it's just applying a current to the battery for a period of time, there is a caveat. Note that if you use delta V peak to end the charge, the dropoff at the end of charging a NiMH is much less pronounced than with NiCD. This means a NiCD charger that's not specifically designed to charge NiMH may false peak or not detect the peak at all when charging a NiMH which can lead to an undercharged or worse an overcharged and damaged battery.

Trickle chargers that charge at up to around 300mA are pretty much interchangeable though.

Decision is up to you, but if your friend is going to use NiMH, it's best he get a decent delta peak charger that's designed to detect the peak in that type of battery.

- James

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