Mili Amp hours

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6 February 2011 at 21:18 #29750
Sam Evans
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@samevans47801
can anyone tell me what Mili Amp Hours are? I know they’re somehow a measure of battery capacity, but what will an RC model with a high MAh battery do better than one with a lower MAh?

Also, is it possible to add up the MAh values of battery cells? so if you couple up 2 1000 MAh cells can you get a 2000 MAh cell pack?
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6 February 2011 at 21:18 #5110
Sam Evans
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@samevans47801
6 February 2011 at 22:15 #29751
Charles Oates
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@charlesoates31738
1000 mah = 1 ampere hour.

Basicly, it’s a measure of how much power (amps) the battery can hold. If a battery is 2 amp hours (2000mah) capacity, it would run a motor that draws 1 amp current for 2 hours. So, the bigger the capacity, in terms of ah (mah) the longer the motor would run for. A bigger capacity lasts longer.

That answer will do nicely to give you the idea of what the term means, but in reality it’s a bit more complicated. The actual running time for a given current will vary with battery type,and the current drawn as some batteries capacities depend on the actual current taken.

In practice don’t worry too much. If you are getting the running time from your 1000mah battery that you want, you don’t need to upgrade.

To answer your last point, yes you could join them in parralel, BUT I certainly wouldn’t. Any slight difference in the packs will lead to problems very soon as 1 pack will charge / discharge differently to the other. Profesionaly made packs of this type have carefully matched cells.

I hope that helps, if not get back on the forum.

Charlie.
9 March 2011 at 18:51 #30043
Brian Morris
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@brianmorris30448
my bantam charger denotes that the7.2v MIAH Battery has terminated its charge having reached 8.9volts ,however its capacity only reached 645mah well below its 4600mah capacity . is this because it hasn,t been cycled .and the memory effect has reduced its capacity Regards Brian
10 March 2011 at 10:56 #30044
Telstar
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@telstar
Hi Brian Your charger tells you how much has been ‘put in’ to the battery. If however the battery has not been fully discharged the value shown will be below the maximum for the battery. Most cells have a designed max capacity, when you try to exceed this, the voltage will rise above the nominal value for that type. (your 7.2V up yo 8.9V) If you then only partially discharge it, (say 1A for 1Hr 1000mAHr) when you recharge it will not need 4600mAHr to recharge, and the charger will stop it when it considers it fully charged.

If the charger has a cycle program then running this will give you a good indication of how ‘good’ the battery is by fully discharging, then fully charging the battery (between its max and min safe voltages). You don’t need to do this all the time, but now and again helps to stop memory effect

Cheers Tom

Sorry Sam I missed out your question. As Charles said 1AmpHour is 1000milliAmpHour theoretically you can run a 1Amp load (motor?) for 1Hour or a 2Amp load for 1/2Hour etc. Connecting batteries in Parallel will increase the overall capacity, BUT the batteries MUST be the same Voltage (putting a 7.2V in parallel with an 8.4V battery is a recipe for disaster) , also the state of charge should be the same. It is something that shouldn’t be done without considerable care and knowledge. IF however you must do this then a simple device using diodes can reduce the risk of damage. Look at Dave Milbourn’s website www.action–electronics.co.uk/ for one of these

Cheers Tom

Edited By Telstar on 10/03/2011 11:17:44
10 March 2011 at 13:34 #30047
Brian Morris
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@brianmorris30448
Thanks Tom , i wrongly presumed that the charger was telling me what was in it at end of charge ,now i am much clearer . i have started cycling my batteries today ,although it seems to take some time.thanks again

Note ,is there a device that would tell you the capacity??,or dowe assume that when full its what is on the label .?
10 March 2011 at 15:49 #30048
Telstar
Participant
@telstar
Hi Brian To the best of my knowledge it’s a matter of trust. It’s only when your battery lets you down, short run time or lack of performance, that you have to doubt the battery. Even then it’s a case of “did I charge it last night?”. The only check I’ve found is to make sure you charge it fully, then see how long it lasts with a known load(a resistor or light bulb). These new ‘processer managed’ chargers can handle this easily, (if long windedly). I do tend to trust my charger (a processer managed one) if it gives a short charge time its because the battery was not fully discharged and it was just topping it up. Once in a while I use cycle to ‘reset’ the battery to a known state, (a bit of conditioning)

In good condition a fully charged battery should hold its labled capacity, as they get older and/or misused they loose capacity.

Cheers Tom
10 March 2011 at 17:44 #30050
Brian Morris
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@brianmorris30448
thanks Tom
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