How long is a piece of string?

I am certainly not an electronics specialist, but my understanding is that you can charge batteries at different rates, so you select the amps for the time you want to take.

A convenient rule of thumb is that a slow charge is 1/10 of the nominal capacity of the battery for 14 hours. Every battery should be able to accept that. So you could charge a flat 4.6Ah battery at 0.5amps for 14 hours.

Some batteries can take a 'quick charge'. So your battery might be able to take a 1.2A charge for about 5 1/4 hours. Or a 5A charge for 1 hour. Or a 20A charge for 15mins. The battery should indicate what the maximum charge rate it can accept without blowing up is!

Of course, the battery has to be 'flat' for the full charge to be correct. More complex chargers can detect when a partially full battery is fully charged, and shut themselves off at that point…

I should think I've supplied sufficient info to enable an exact answer

The exact answer, as I wrote above, is 5 1/4 hours. You will see that written in the 4th paragraph down. My calculation actually made it 5.38 hours, or 5 hours 23 mins. If you want any more precision, we will need to see the precise specification of the battery, since charging efficiency will vary depending on battery type.

Edited By Dodgy Geezer on 18/07/2015 13:30:23

Edited By Dodgy Geezer on 18/07/2015 13:31:24

Edited By Dodgy Geezer on 18/07/2015 13:35:05

Bob. One would have thought the Turnigy charger is automatic and would cut off when the battery is charged?? or is that not the issue?

I have batts charging at the moment and every now and then I pop in and if one of the charge lights is green I unplug that one and put another in.

Ashley

Hello Bob

This subject is way out of my field of expertize, just like Ashley I plug them in and forget them until the green light pops up. However I have found this site a useful rule of thumb guide. **LINK**

Paul

Sorry all the link didn't work

Edited By Paul T on 18/07/2015 15:48:14

Bob

Which Turnigy charger are you using, what make and cell size of batteries and how many in the stack, finally how old are the batteries and how many cycles have they had.

Paul

in the old days, we used to fast charge them in about 15 mins

What further info do you need to know?

So you were using a 20A charger? Or the batteries were not 4.6Ah? 4.6Ah is rather impressive for 'the old days'…

So it looks like…..4600 / 1200 = 3.8 hours……( Why does DG say 5 1/4 hours?)

Because there can be considerable inefficiencies in transferring energy from a charger to a battery. You can see this from the 'rule of thumb' that I used, which suggests that to charge a battery you give it 1/10 of its nominal amp output, not for 10 hours, but for 14. That's an old estimation, assuming a 70% efficiency – I wouldn't be surprised to find modern batteries to be much more efficient. You can also get a reduced charge rate if the charger has a constant voltage phase – again, I don't know what charger you are using. I googled 'Turnigy 1200', but that didn't provide a clear answer….

Now different batteries all have different characteristics, and as they age the characteristics change, so I can't be sure of what your battery wants, or will take. I suggest that if you were charging a 4.6Ah battery with a 1.2A charger for 40 minutes you were not charging it to full capacity – though I don't know how discharged the original cell was. Charging fully in this time from flat requires a 7A charger – 10A allowing for inefficiency.

Note that the first part of the charge puts most power into a battery, and the last part puts less in. You may find this reference handy:

**LINK**

Edited By Dodgy Geezer on 18/07/2015 17:15:11

Why do you say that I may have been leaning rather heavily on my batteries?

Because your set of NiMH 4600 (sold by Component Shop?) has 6A recommended at maximum charge rate, and my calculations suggest that you have been using 7A.

Of course, this is an estimate based on my estimate of your charging current (which might be wrong).

which is why I said 'may'…

Reading the manual, if you set max charge rate to 1.2A and mode to 'manual', you will get 1.2A. And that should charge a fully-flat 4600 pack in a minimum of 3.8 hours (as you stated) – though I would not be surprised to see it take 5. If it takes much longer or much shorter there is either an issue with the battery pack, or you are not actually charging at 1.2A.

If you are flattening the batteries each run you should not need to recycle. Ideally, of course, we could do with an electronics buff to give us some definitive comments…

Edited By Dodgy Geezer on 19/07/2015 22:03:02

Bob,

If you have your charger set to 1.2 amps and your 4.6Ah batteries are flat then the charging time MUST be at least 3.8 hours as you are only putting 1.2 amps per hour into the battery. If the battery is not actually flat then the charging time will be reduced depending on how much charge is left in the battery after you last used it.

If you charge at the maximum recommended rate of 6 amps then the charge from flat will; be 0.75 hours or 45 minutes and things may get a little warm.

Generally batteries respond better to lower charging rates which increases their longevity (please be gentle with me!)

As DG says, the precise characteristics may vary things a bit but the basic arithmetic remains the same.

If you have abused the batteries by high discharge rates into the motors then they may no longer be able to hold their original nominal charge.

To get the best out of any electronic components, including batteries, it is always best to run them within their nominal maximum limits.

As a rule of thumb, if something is getting very warm or hot then the installation is not operating at optimum efficiency.

Colin

Edited By Colin Bishop, Website Editor on 19/07/2015 23:34:04

Hi Bob, I’ve followed this thread with interest, as I’m sure have many others. It seems to me that you are on a steep learning curve with this subject, and may not have fully appreciated the full and correct answers given, especially by D G..
As you have an excellent charger with automatic charging settings, I implore you to make use of that feature,it works very well. Change from manual to auto and let the technology do its job.