Jump to content
Sign in to follow this  
Kalameja

Battery Charging Basics

Recommended Posts

I've read that in order to determine how long to charge a 7.2v NiMH one should divide the total number of battery mAh by the DC output of the charger, also mA, and factor in a 20% fudge factor. 

In my case that would be for my 7.2v 5300mAh battery over 35 hours!! Can that be right?

5300mAh for battery/ dc output of charger of 150mA  + 20% fudge factor = > 35 hours

Should I purchase a battery with a lower mAh? I had read that the higher the mAh of a battery the longer and better performance you could expect. 

Can someone suggest a charger that has a higher DC output of  150mA? I only have a simple cheap charger that plugs into the wall like a cell phone charger. Any other suggestions?

 

ek

Share this post


Link to post
Share on other sites

Yes that pretty much sums it up, as much as i need to know anyway. There will probably be a few people on here that can explain it better, especially the fudge factor! I ask an electrical engineer mate until i think i know enough. 

 

Anyway, i have a very basic charger which sounds just like yours and is 700mA which cost about NZD$12. This charges a 3800mah nimh in about 5-6 hours depending how flat the batt got. I also have a proper charger for lipo which balances etc, but don't use it for the nimh even though it does all types. 

 

How serious are and whats your end game? If bashing is it and you will stick with nimh then just find a better version of what you have. You can buy 8 of them for the price of a decent charger. If you want to go racing then you will probably need to go to lipo, so will need the better charger in future anyway. Also how many batteries do you need to charge at once? I have 2 cheap chargers so i can keep both my car and my sons charged easily. 

If you stick with cheap chargers then a cheap voltmeter/multimeter is useful too to check how charged they are, instead of what i used to do in the 90s and if it felt warmish then if was probably fine!

 

Oh yeah, those charge leads that connect to a car battery, do they still work? I assume they do, that would be the quickest, probably 40min or so

 

 

  • Like 1

Share this post


Link to post
Share on other sites

You can get chargers with multiple output settings. I use the Dynamite Prophet Sport NIMH. I run 7.2v 3000mah NIMH batts and can charge one of them full in about 50-55 mins on the 3a setting. It also has several other settings for current (.1a, .5a, 1, 2, 3, and 4) I believe. You choose the amp setting then hold down charge, it begins the charge and it shuts off when complete. :D

  • Like 1

Share this post


Link to post
Share on other sites

Yeah, 5300 mAh / 150 mA = 35 hours.  If you want to use your car more often than once every two days, a better charger is needed.

Generally you can safely charge NiMH batteries up to 1C charge rate; in this case you could charge your 5300 mAh pack in ~1 hour using a 5 A charger.

This works fine for $28:  https://hobbyking.com/en_us/imax-b6-50w-5a-charger-discharger-1-6-cells-genuine.html

And you'll need a power supply for the charger; that's another $15:  https://hobbyking.com/en_us/hobbyking-105w-15v-7a-switching-dc-power-supply.html

Plus a charging lead for $4:  https://hobbyking.com/en_us/tamiya-and-t-connector-multi-charge-plug-adapter.html

Or similar equipment from another supplier.  In the short term, the value of the setup is it will definitely charge your battery faster.  In the long term, you can change over to LiPo batteries later and still have a valid power supply and charger.  You may need a different charging lead at that time.

 

  • Like 1

Share this post


Link to post
Share on other sites

I started off with the most basic of chargers and yes it takes hours!

Next was a multiple output charger, it detects the delta peak and then reverts to a minute trickle charge, i.e. it knows when it is charged and effectively shuts down.

In addition when I bought 2 new batteries I also got in another charger that is a single output but shuts off.

It is a bit excessive, but I keep the third charger at work and after a weekends bashing I can charge up all six batteries in rotation at work (using their electricity! ;) ) and also I'm there to swap them round, so it gets done fairly quickly.

Prices were £25 for the multiple outputs and the single output was included in a deal with 2 batteries for £40.

  • Like 1

Share this post


Link to post
Share on other sites

Buy a better charger... trickle charging makes battery performance very lacklustre.

NiMH for RCs best done at around 3-4A with a reliable peakdetect charger specifically for fast charging NiMH (they're different algorithm to nicads). 

Don't have much confidence in any subC cells labelled above 5000mAh... IMHO bit optimistic, have doubts anything much improved since 3800-4200 mark. Best not to go pumping 5A into them if you can avoid it.

  • Like 3

Share this post


Link to post
Share on other sites

Some NiMh packs actually like being charged at more than 1C. I have a 3Ah Hobbyking NiMh pack that I routinely charge at 4.5A (so 1.5C) and it's the best-performing NiMH pack I have, actually on par with a Lipo for the first few minutes of a run in a non-demanding car. (After 2-3 minutes, the Lipo's keep going where the NiMH starts to lose Volts)

Your mileage may vary though. ;)

  • Like 1

Share this post


Link to post
Share on other sites

Don't u think waiting nearly an hr to charge is such a drag?

Early days we charged nicads in only 15mins!! :blink:

Only 1200mAh but hey :lol:

haha recently I rediscovered a 2000 nicad pack. Looked dead but I stuck it on the charger and it woke back up... AMAZING! Took a charge, still pumps out juice fine.

Wouldnt be trying that with any 0V lipo...! :o

  • Like 1

Share this post


Link to post
Share on other sites

Still running 4 2400 NiCds got them used as giant plane stickpacks.

yJgNS4EvIG94sWv66ImR4t_3UYk9epE5lQkUgr2O

 

Share this post


Link to post
Share on other sites

only ever got 1 pack of 2400s :( they were good! But batts weren't cheap back then.

nowadays I'm told nicads are banned in many places... gah, greenies hate heavymetals <_<

had to go looking for stickpacks as that's the only thing that'll fit CC01 without hacking. Battery slot has slanted rear edge so I don't think I can even carve it out square to fit lipo like on DF01. 

Share this post


Link to post
Share on other sites

I have one Nicad at 1600 mAh, which is about ten years old and it holds a charge nicely. And yet another Nicad from probably back in the 80's. It's so old it still has the hump! I've yet to attempt to charge it. I think I'll wait until I pick up a better charger. 

 

 

Share this post


Link to post
Share on other sites

bad news, "1600" nicads are usually basic commodity cells

there's a trick with nicads, observing whilst growing up with them - the cutting edge cell technology B) always went to RC usage first... 

for a long time capacity stayed at 1200, mainly Sanyo. Later Saft & Panasonic joined in. With 1200mAh you prayed HARD that your car would last the 5min race :rolleyes: but that's FUN because you could just be top 3-5 at the 4th minute and just cruise... hoping your leaders would dump before the finish. Often they do...

then batts jumped to 1700 circa 1988... but early yellow SC cells are fragile. Later Sanyo made High Discharge versions in Red SCR... these are legendary (for their time)

next jump was 2000 blue... pretty good generally, weaker ones probably par with a good 1700SCR

final iteration for nicad were the Sanyo red rainbow 2400 shown above :wub: good voltage good capacity good punch.

Sanyo fell behind, by then subCs moved on to GP's orange green NiMH 3000! Voltage and punch a bit weak and some applications a good 2400 might beat it, if you didn't need all that capacity.

3000, 3300, 3600, 4200... zero chance of dumping before the end buzzer now :ph34r:

These days when you buy any generic RC pack that's not the highest capacity available, the cells are often either rejects from testing for higher capacities &/or just any old cell that's meant for building into cordless tools.

Cells that aren't built for High Discharge will boil their electrolyte and vent; tool grade cells might not even like being fast charged before they vent.

Share this post


Link to post
Share on other sites

Needed a battery to test and setup the electrics for a new build at the weekend.  My NiMh was in a box and I couldn't be bothered to dismantle half the garage to reach it, so I used a NiCad that I bought 25 years ago, and probably haven't used for maybe 12.  It worked fine.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...