Go Down

Topic: 4x AA Ni-Mh voltage drop on load (Read 11867 times) previous topic - next topic


Aug 15, 2014, 07:47 pm Last Edit: Aug 15, 2014, 07:56 pm by danielb7390 Reason: 1
Yes i understand...
As i said before the car used to have a 9.6v 620mAh battery. It's this one.

I measure before the motor draw at full throttle it was around  8v@400mA.
Now there's the direction motor but its a simple dc motor like this:

Also the draw from the Arduino but that's little.

The comments for the batteries look positive!


Well, i got a laptop battery its 10.8v 44.8wh, already found the pinout and turned it on and got the 10.8v out.

Is it a good battery? I believe  its good just in doubt if it will not blow up in my face!

And yes battery is good, i tested it.
To charge it i would use the laptop it came from it still charges the battery, its just a barebones motherboard.

I followed this: kuzyatech.com/testing-laptop-battery-pinout-smbus-charge-capacity
The battery looks the same


Hi, can you post a picture of how you are setting everything  up please.

Tom....... :)
Everything runs on smoke, let the smoke out, it stops running....


Just wanted to know if that battery is a good bet or no...


Most laptop batteries are LiPo and need to be charged and discharged properly, or they can be destroyed in the very first use.

I have obtained good quality batteries at reasonable prices from http://www.all-battery.com/


Its a Lithium-Ion battery,
For what i found on the net it has a protection circuit so that shouldn't be a problem also the charge i will charge it on the old laptop it came from.

Or not?


Most laptop batteries are LiPo and need to be charged and discharged properly, or they can be destroyed in the very first use.

I have obtained good quality batteries at reasonable prices from http://www.all-battery.com/

Most laptop batteries are _not_ LiPo, they are lithium ion, not lithum ion polymer, which is
much more dangerous (for instance must never be charged unattended).

The normal recommended regime for laptop batteries that I've heard of is to fully charge
and discharge them about 8 times when new, then occasionally subject to a full discharge/recharge to maintain capacity.  And yes all lithium batteries must always
be charged and discharged under proper battery management (which will be the case in a
phone or laptop).
[ I DO NOT respond to personal messages, I WILL delete them unread, use the forum please ]


So it can work for me?
I suppose the circuit inside the battery protects the cells so no problem there?

Also i will try to connect to smbus to get the battery charge level and other info


Thanks for correcting the typo, Mark!


Oct 04, 2014, 05:58 pm Last Edit: Oct 04, 2014, 06:03 pm by danielb7390 Reason: 1
Well managed to connect to the battery gauge chip, and tried to use a 12v fan on it and worked ok.

Code: [Select]
Voltage: 12.00 V
Temp: 25.15
Current (mA):0
Capacity (mAh):3229
Charge %: 100
Charge % of designed: 81
Capacity Remain: 3227
Capacity Total Charge: 3229
Capacity Designed: 4000
Voltage Designed: 11.00
Cycles total: 296
Manufacture Date: 2008-10-8

Its quite good for the date it was manufactured!

My question is since now i can access the charge level and stop using the car when its bellow certain %, its safe to use?
As i already said i'm charging it on the laptop it came from so no problem with charging!


NiCad or NiMH batteries, and even LiIon/LiPo batteries, and every other battery out there, suffer from something called internal resistance.  Your high capacity made for cameras kind of battery that you paid a lot of money for generally isn't worth the price. The name brand find it in the grocery store battery is made for the general person that doesn't know any better, and truthfully doesn't really need any better. Also the battery packs for RC Cars that come from a Toy store are crap, they weren't designed for a high discharge, they were designed for very low performance cars.

From what you have described you need hobby grade batteries. The kind of battery that you purchase from a hobby store, no not Radio Shack (bad juju) but from a store that sells primarily RC Cars, Planes and Helicopters. Again not Toys R Us or a store that primarily sells other than Remote Control Vehicle products. You can find these batteries online at hobby stores as well (not sure of the best option for Portugal). The batteries used in RC Vehicles are designed for high discharge, high discharge in the effect of several amps used often in less than 10 minutes (less than 5 for RC Helicopters). That goes for all, NiCad, NiMH, and LiPo.

I recommend the hobby stores mostly because it's a much easier way of finding these batteries. They aren't exclusive to the hobby field, but a good hobby store is going to give you a good range of battery capabilities, and they're lowest grade battery should still exceed the common grocery store battery.

I recommend those because of the voltage drop you are reporting. On new, freshly charged batteries your voltage should not drop below nominal. As stated before, nominal is 1.2V per cell for NiCad and NiMH.

As for your Laptop battery........... DO NOT GO THAT ROUTE!!!............  If you are going to use a lithium battery get LiPo in a 2 cell set up, preferably in a flat cell. The battery pack might have some kind of discharge protection, but even from big name brands I wouldn't trust my house, office, my neighbors house with the pack, unless of course the laptop that it was designed to be in was what it was being ran in. Not just the charge, but the discharge.

Currently The vaping crowd (e-cigarettes) is learning about charging and discharging LiXX batteries that the RC hobby world learned about 10 years ago.  If you want some nice after pictures of an unrespected Lithium battery go to an rc forum such as RC Groups, and search lipo fire.

Most lithium fires don't happen in the discharge, but the discharge can be the cause.

I am not trying to stop you from using a lithium battery, but want you to use a proper set up. Hobby Grade Charger, with Hobby Grade Batteries.

Flat packs are better than round cells, although the round cells are rigid, they do not compare in capacity and discharge capabilities that a flat pack has.

I have thought about using LiPo's to power a number of items but haven't yet because of the voltage cutoff necessary. It would need to be set up so that at 3.4v or 3.5v per cell, yes they claim 3.1v per cell, but for longevity and safety the higher voltage is much better. For the cutoff it needs to be absolute, ie once it cuts off there is no more draw no matter how small once the low voltage limit has been met. maybe a relay that turns on when you turn on the circuit, and then when the limit is reached it cuts all power? I haven't worked on it yet.  You do not want a software switch to turn off the circuit because they draw power even though they "turn off" the circuit. They may only draw a few mAh in an "off" state but they still draw power, and if you don't get to them for a few hours, those few mAh it draws could set your batteries to undervoltage which destroys them (or should for safety).

My resume in batteries is 12 years experience with using them in RC Airplanes and Helicopters, and a little more recently in RC Cars. With proper handling, care, and maintenance I haven't had any of my own batteries fry, although I have seen others lose their entire vehicle in a blaze of glory.


Oct 05, 2014, 11:10 am Last Edit: Oct 05, 2014, 12:07 pm by danielb7390 Reason: 1
Easy to say not so easy to do! I can't seem to find any good battery for good price!
I have already spent way to much money i cant see any result and this is driving me mad!  =(
I find nice battery's in a uk site but then they want almost the same for the shipping because its lipos and its dangerous and have to pay extra to the mail company... ebay they can be good or not ...

Also i still don't get it this battery should at least be ok for a 1C discharge no??
The motor draw 600mA@10v and when stalled 3A@10v, but that situation would be avoided to avoid over current...

What about a power drill battery? That must be rated for high discharge! Cant remember the capacity but it was very high!

Also if i can't use the battery for the car, can i use it for something else safety? Like max x current?


a quick search turned up www.rtr-modelismo.com and the single cell NiMH Batteries I saw on there were about 4.25 euro? that's not too bad of a price for quality NiMH batteries... I would presume the battery pack from a large brand cordless drill would have good batteries inside of it as well, DeWalt comes to mind, basically any cordless you'd expect to find at a construction site. 

It might be a bit of a stretch for 5+ cells for a battery pack, but it should fully provide for what you need, and continue providing for a long time.

Some one mentioned the Capacitors to reduce the ripple, even on a short lead (less than 2 inches/ 5cm total), a capacitor pack would be a benefit. If the leads are longer you may want a second Cap pack... sadly I don't know what the proper set up should be, I have in the past used speed controllers with them built in, and don't have long leads. the other posts recommendation is probably good.


I wanted a pack already done... most of them are 7.2v i doubt the motor will like it i needed something more on the 9.6v range..

I have seen this: http://www.amazon.co.uk/gp/product/B002TSKO5W/ and http://www.amazon.co.uk/gp/product/B006FHUBCE problem is all this is 70€! And the reviews of the charger not the best...

It seems i must forget this project its getting way out of price...

Go Up