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Using Arduino => General Electronics => Topic started by: danielb7390 on Aug 14, 2014, 11:40 am

Title: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 11:40 am
Hi,
So i got this new batteries (http://gp.batteries.pl/collection_uploads/gp_recyko_aa.pdf (http://gp.batteries.pl/collection_uploads/gp_recyko_aa.pdf)) already used twice to charge my phone and works great.
Now that i got home back to my electronics i was trying to power a router with them. Here's the info:

Router: 240mA@12V (measured by me with the multimeter between the ground wire)
Batteries: 4x 1.2V 2050mAh(typical)
Dc-Dc boost converter from ebay

They sit around 5.2V unloaded, but as soon as i plug the load the batteries voltage drops to almost 3.5V! Because of this the converter goes mad and drops the output voltage too....
According to the data-sheet they *should* go up to 6A discharge..

And no its not the converter tried with non-rechargeable batteries i have (6x C +-8Volts) and it works...

Any help would be appreciated!
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: TomGeorge on Aug 14, 2014, 12:04 pm
Hi, show us the DC-DC converter, what are you using for wiring and how are you holding the batteries.
Have you measured each cell when they are under load to check if they are all dropping in output or just one?
Sounds like they are not fully charged.
Can you measure the current being drawn from them when the fault occurs.
Also the current being drawn with the C cells.

A picture of your setup would help.

Tom...... :)
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 12:21 pm
The converter: http://www.ebay.com/itm/310717070508

I also thought of the charge I'm changing again just to make sure but i charged them yesterday and stored they should be good...

The current draw when it drops it increases a lot i saw 2A@-+3.5V from the batteries and then disconnected the wires.

Will try again with the AA when the charger gives me a green light!

Tests with the 6x "C" batteries:
I set-up the output around 12V for this test.

Battery  Voltage without load: 8.73V
Battery  Voltage in load: 6.90V - 7.10V (It jumps a bit up and down)
Battery Current Draw: 0.55A max

Output Voltage: 12V
Output Current: 0.26A

As for the picture i'm just using alligator clips to connect the things. Also i was using a battery holder to rule it out i tried with the batteries in a row and connect the alligator clips in the end by hand, same result.

You think this batteries are not enough?
Thanks for the help!
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 12:52 pm
First of sorry for double post but the other one is big enough already...

The batteries just finished charging witch means they were already charged...
Fresh from the charger: 1.45V, 1.45V, 1.44V, 1.44V

Pack unload voltage: 5.77V
Pack Load voltage: 3.35V

Load voltage Bat #1:1.32V
Load voltage Bat #2:1.31V
Load voltage Bat #3:1.30V
Load voltage Bat #4:1.23V
Total sum of bat voltages: 5.16V

This is strange.. the total of each cell is bigger than what i'm getting in the output how can this be?

Load Battery draw: 1.30A
Load  Battery voltage: 3.10V (its starting to drop from the above test...)
Output Current: 500mA
Output Voltage: 6.50V (should be around 12V that's what i set it to)

If i can do any more tests please say.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: TomGeorge on Aug 14, 2014, 03:00 pm
Hi, with 4 Nimh batts thats 1.2V x 4 = 4.8V. Thats using the nominal voltage per cell, so thats okay.

Try putting a capacitor across the Nimh, say 470uF or 1000uF, and a 0.1uF as well, you may be getting problems between the ripple current from the SMPS and the internal resistance of the Nimh.
Keep the leads between the Nimh and the supply as short as possible.

http://www.ti.com/lit/ds/symlink/lm1577.pdf

The spec sheet even shows an example circuit, 5V to 12V.

Tom......... :)
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 04:00 pm
Still same...

On the output i placed a: 2220uF 35V cap
On the input i placed a: 2200uF 16V AND a 104 ceramic cap

Same, with the big one in the output if i let it charge up before plugging in the router it decreases slower but ends up in the same...

More ideas?

EDIT: Just tried with 4xAA normal ones and same problem happens! I'm starting to think the voltage in the input is too low for the converter... this ones drop from 6.30V(no load) and 3.72V (load)

EDIT2: With 5xAA IT WORKS! (7.80V)
Now its safe to assume that the input voltage is the problem?
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: polymorph on Aug 14, 2014, 04:40 pm
In my experience, many alligator clip-leads use -very- small wires that are poorly crimped in place. I went through all mine and soldered them, or replaced with larger wires. Some sets of my clip-leads had what looked like about 24 to 26 gauge stranded wire, of not very good quality.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 04:46 pm
But if it was that it wouldn't work with the other "C" batteries...?

With 5x AA making 7.80V input it works, with 5xAA making 7.40V input same problem...

About the alligator indeed they seem very bad crimped when i can i will solder them or maybe change the wire in some of them with wire i got from a pc psu!
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: polymorph on Aug 14, 2014, 05:00 pm
All the voltage drops add up. So if you start with a higher voltage, maybe it works.

There is also the matter of corrosion on the ends of the cells.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 05:03 pm
Well the rechargeable batteries are new, same for the normal ones.

EDIT:  :0 REALLY??? Just connected with just 4 wires and guess what it works! Even with the rechargeable ones, safe to assume alligator clips are the culprit ...

Its drawing:
2.76V
1.30A
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: elac on Aug 14, 2014, 05:05 pm
You need higher capacity at 4.8V, those modules will boost 4.8V to 12V, of course the efficiency is very poor.
You will need to provide 600mA @4.8V plus whatever the mA the module consumes for reliably running 240mA @ 12V.
That's over 25% of your total capacity.
To avoid large voltage drops on your supply keep the load to 10% of your batteries capacity.
So to reliably run 240mA @ 12V  from 4.8V you should have a battery pack with an 6aH capacity.
With a booster module it is most efficient to keep the supply voltage as close to the load voltage as possible.
At 9.6V you would need 300mA plus the mA the module consumes, so a 9.6V battery pack with 3aH capacity would also work.
But what about this question, how long do you want run the load for?
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 05:21 pm
Its drawing:
2.76V
1.30A

It's wrong! I was still using the aligators to measure the current, changed to my multimeter probes and it gives total different results!

5.12V
800mA

Now thats better!
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: polymorph on Aug 14, 2014, 06:25 pm
Where are you measuring that? At the power inputs on the regulator, or at the battery terminals?
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 06:31 pm
I don't know if i follow you?

The CURRENT I'm measuring in-line between battery GND and the GND input of the converter.
The VOLTAGE I'm measuring in the GND and VCC of the input of the converter.

I just have it like this and its working perfect: ( AA + AA + AA + AA) --- DC-DC --- Router

This alligators really need some better solder/cable they all show the same problem  :P
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: elac on Aug 14, 2014, 06:36 pm
Better?
Batteries: 800mA @ 5.12V = 4.096W
Load: 240mA @ 12V = 2.88W
Module consumes 1.216W
Not very efficient.
Total power of the "batteries in perfect world" @ 5.12V = 10.24W
Shouldn't drain your batteries more then 50% or 5.12W of power to safely use.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: polymorph on Aug 14, 2014, 06:48 pm
If you are measuring voltage at the input of the regulator, then that includes all the voltage drops along the way. I thought it would be unusual for a NiMH cell to drop that far in voltage.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 07:05 pm
@elac
It's better because its working  8)
There's any way to make it more efficient?

@polymorph
Before i also read the voltages on the battery pack it was same result.

If im making this right this setup should be able to run up to 2h almost? or I'm wrong?

One of the problems is the router(s) i have 2 i can use, both of them have another dc dc converter inside them! They used those linear transformers...  And yes tried direct to batteries but the voltage is low... it boots up but when connecting it drops.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: elac on Aug 14, 2014, 08:18 pm
It's not good to drain the rechargeable batteries until the router shuts off, that will be well below the recommended discharge.
The boost module will keep boosting until there is not enough current or voltage to do so, regardless of the battery pack's state of charge.
Go with your assumption that the router will run for 2 hours and see how many cycles you get before the time your load runs becomes dramatically lower or your batteries won't charge properly.
Be aware that as the voltage of the batteries drops the modules efficiency gets worse.
For better efficiency raise the voltage of your battery pack.
2 x 9.6v battery packs in parallel a 4aH total capacity will give you around 2aH of useable current or 19.2W.
That you could safely say will run your router for 2+ hours.

As for adding another router, it might "work" for you, but with your current setup it surely will not be "properly working".
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 08:36 pm
You guys keep talking of battery packs problem is i cant seem to find anything for a good price!
On ebay  most of them are fake, local stores only have this batteries for digital cameras where can i get nice batteries from??

I wasn't going to run it until it shuts down, i was going for around 1v/battery 4v total pack.. isn't that the correct discharge voltage?
Also if i get more 4x AA and connect in series i should get 8x1.2 = 9.6v would that be better??

This is part of a bigger project, im converting a rc car to wifi controlled it already works perfect problem is the batteries!
The car itself used a 9.6v 900mAh battery and my friend said it would run for around 30minutes, if i bought 4 more to join like i said above would it work? I don't need huge runtime at least 30min it would be nice :)
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: retrolefty on Aug 14, 2014, 08:39 pm

You guys keep talking of battery packs problem is i cant seem to find anything for a good price!
On ebay  most of them are fake, local stores only have this batteries for digital cameras where can i get nice batteries from??


Those designed for digital cameras should work fine for servo application as both are higher current/shorter duration type loads. Any battery will have some limit of number of servos that can be manipulated simultaneously due to the specific battery's internal resistance rating.

Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 08:49 pm
The ones i got were on the digital camera section. I really didn't have much to choose from: gp or varta or sony it's the ones i saw in the stores around here...
If i can be sure that buying 4 more will solve all the problems... otherwise seems like the wifi car will get stuck... at least my LED screen is almost done  :smiley-roll:
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: elac on Aug 14, 2014, 10:04 pm
With your current setup using 800mA @ 5.12V, 2 hours of run time will be 1600mA or around 80% of your batteries total 2050mA capacity.
For only 1/2 hour of run time this is fine as you are only discharging the batteries about 20%.
But, you are pulling 40% of the batteries total 2000mA capacity to achieve this voltage boost, which is not the best for the batteries as that current has to go through the batteries internal resistance. More current = larger voltage drop = wasted power(heat) = faster wear down of the batteries.
Most 9.6v RC battery packs like the ones sold at Walmart are nothing more then 8 X AA's in series.
So a DIY 9.6V battery pack consisting of 8 x the batteries you are already using will give you around 2Ah @ 9.6V which is 19.2W total power and about 9.6W of useable power.
Your 12V 240mA load draws 2.88W of power plus the power of the boost module, whatever it is at a 9.6V source voltage.
You will be able to get around 2+ hours of run time at about a 40% discharge, but for how many recharge cycles?
More then your current setup, but also much less then the batteries rated amount of recharge cycles.
If you double the Ah capacity to 4Ah @ 9.6V and properly care for the batteries you could safely run the router for 2+ hours daily. This way you can get much closer to the batteries rated amount of recharge cycles as you would be around a 20% discharge for each 2+ hour cycle.



Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: MarkT on Aug 14, 2014, 10:51 pm
When you say 4x AA NiMH pack, are these cells a pack, with spot-welded tabs,
or just 4 cells in a battery holder?

If a battery holder your problem may be the battery holder is not designed for high
current and has steel springs and rivetted contacts - these are hopeless above about
0.5A.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 14, 2014, 10:58 pm
@elac
If i need all of those just for the router don't even want to know how many i need for the rest of the rc car...
Seems like this project is going to end...  i paid 20€ for this 4 batteries ... if i need to get all of those... its way too pricey...
Don't know if makes difference, but it would be to use at worse case one a week... would that help?
Also with 8x AA router shouldn't need a external dc-dc converter since the internal one works with 7v+!
Did you take a look @ the data-sheet i placed on the 1st post?

@MarkT
Yes they are separated cells (bought with the charger).
And yes im using the battery holder but i don't see a problem there its not getting hot at all.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: MarkT on Aug 14, 2014, 11:42 pm
The bad battery holders can drop more voltage than the cell's internal
resistance, that's the point.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: elac on Aug 15, 2014, 12:59 am
Ok, let's read that data sheet where it says "Recommended discharge current 200 to 6000mA".
That being 200mA steady draw which is 10% of the 2000mA nominal capacity @ 1.3V up to 6000mA pulsed @ 1.17V.
Running the router off the internal regulator from 9.6V or 7.2V will definitely be more efficient then the 2 step process your trying to do as of now.
And it will eliminate the frequency introduced by the booster module into the RC circuitry.
Take what MarkT said about the battery holder and put together a proper pack or purchase one.
It will also prevent the batteries coming out or bad contacts when the RC is bouncing/vibrating.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 15, 2014, 05:12 pm
I would love to get a battery pack problem is WHERE! Any legit ones on ebay? Amazon UK?
You guys on USA are just lucky... can buy this kind off stuff in lots of places...
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: elac on Aug 15, 2014, 07:05 pm
Like this (http://www.amazon.co.uk/Digital-Additions%C2%AE-Battery-Pack-Charger/dp/B006OKNPAW/ref=sr_1_3?ie=UTF8&qid=1408122083&sr=8-3&keywords=9.6v+rechargeable+battery+pack) and this (http://www.amazon.co.uk/Digital-Additions%C2%AE-Battery-Flat-Tamiya/dp/B007QSJLUO/ref=sr_1_5?ie=UTF8&qid=1408122083&sr=8-5&keywords=9.6v+rechargeable+battery+pack), both from Amazon UK.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 15, 2014, 07:11 pm
See that's no really that expensive!
Here they want 50€ just for the battery pack    =(

Are those any good? Would those work for the car and the router?
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: elac on Aug 15, 2014, 07:33 pm
Any good, I don't know never used them.
As for them "working" for the RC car + router, if the car needs 9.6v and the router will run from a 9.6v source, then yes they are the correct "working voltage". But that doesn't mean much.
Without knowing the total current draw of the combined RC car + router and how much run time is needed nobody can answer what total Ah capacity you need for your project.

Please post as much detail about your project as possible.
As it is now every answer to your questions is just raising more questions that could be avoided with more details.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Aug 15, 2014, 07:47 pm
Yes i understand...
As i said before the car used to have a 9.6v 620mAh battery. It's this one.
(http://www.wonderlandmodels.com/media/managed/large/9.6v.jpg)

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:
(http://music.columbia.edu/~douglas/classes/Motor_Mania/DC_simple2.jpg)
Also the draw from the Arduino but that's little.

The comments for the batteries look positive!

Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Oct 02, 2014, 07:49 pm
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
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: TomGeorge on Oct 02, 2014, 11:38 pm
Hi, can you post a picture of how you are setting everything  up please.

Tom....... :)
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Oct 03, 2014, 10:15 am
Just wanted to know if that battery is a good bet or no...
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: jremington on Oct 03, 2014, 07:31 pm
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/
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Oct 03, 2014, 07:33 pm
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?
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: MarkT on Oct 03, 2014, 11:46 pm

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).
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Oct 03, 2014, 11:50 pm
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
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: jremington on Oct 04, 2014, 05:47 pm
Thanks for correcting the typo, Mark!
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Oct 04, 2014, 05:58 pm
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!
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: Ritlee on Oct 05, 2014, 06:49 am
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.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Oct 05, 2014, 11:10 am
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?
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: Ritlee on Oct 06, 2014, 05:11 am
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.
Title: Re: 4x AA Ni-Mh voltage drop on load
Post by: danielb7390 on Oct 06, 2014, 10:50 am
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...