I've read that using the IMAX B8 charger is helpful in checking/reconditioning batteries. Looking through Amazon, however, there seem to be many types of IMAX B8 chargers, all claiming to be the real deal.
1. How do I tell whether I'm buying the real deal?
2. Is there a better brand than IMAX for working with NIMH batteries?
3. What's the procedure for using the charger to check/repair batteries?
Any help or links would be much appreciated. Thanks!
I recommend you Icharger.This device has a finer level measurements. And more features.
http://www.hobbyking.com/hobbyking/store/__6609__iCharger_1010Bplus_300W_10s_Balance_Charger.html
Hi,
You are interesed in Checking/repairing NiMH Batteries.
The chargers mentioned are not capable of either of these functions.
The chargers mentioned are balance chargers and therefore suitable for LiPo battery packs and not NiMH, even though NiMH is mentioned in their specs. NiMH batteries don't have or need a balance cable.
For charging NIMH you need a constant current charger such as this.
http://www.ebay.com.au/itm/2-PIN-12V-DC-2A-Power-Supply-Charger-Adapter-AU-Plug-For-3528-LED-Strip-Light-/251272021635?pt=AU_Ele...
If you are interested in flying R/C planes then you could make use of the more complex chargers features.
I will tell you how to test used Vectrix NiMH batteries to build a replacement pack. First the theory of what happens to these batteries in use. The batteries are damaged by over charging, over discharging and reverse polarisation. Side reactions and excess pressure typical of Mi-MH chemistry are higher in these individual batteries. The GP30 prismatic Ni-MH cells are rated at 2C continuous discharge which the Vectrix bike exceeds.
To test individual batteries with basic equipment do the following. Inspect the individual batteries for swelling. These cells are damaged and throw out the swollen ones. Assemble the individual batteries you have left into packs of 8 cells in series. Fit a compression strap around the pack as the cells must be under compression when charging. Charge at a charge rate of 1.5 - 3.0 amps until all individual batteries are fully charged/ same voltage. This will take 15 - 30 hours. Take the pack off charge and write the date on the side. Leave for 2 weeks to allow self discharge of the damaged high leakage individual batteries. After 2 weeks check the voltage of each individual battery. You will notice most of them will be within 0.015 volts of each other. The individual batteries that are below the norm have high self discharge and will cause imbalance in a future battery build. Do not use these batteries. Build a new battery from the individual batteries you have left. Start off with more than you need so you can pick the best individual batteries for the replacement pack build.
A bit of background probably helps - Josh has been trying to sort out the nimh battery in his Vectrix for sometime
The reason we use the chargers like the i-max is because we're capacity testing 102 cells at a time, looking for cells that are dead or dieing.
the swollen short circuit ones are easiest to find, it's the ones that aren't so swollen and not short circuit that are the real pain to catch out
it is exceptionally time consuming to do manually
basically you need to discharge all cells to ~0.4v (ie fully discharged) then put ~35Ah in at between 1A and 2A
then do a capacity test
much easier to do if you have a few devices that will balance at 0.4v, do a timed charge (or better yet do a temp based charge termination), and graph voltage vs Ah
Doing a top balance is only something you would bother with a known good battery - the original vectrix charger does that anyway
by repair we are usually replacing individual cells
In answer to Josh's question - I hadn't realised there were fakes for sale - the imax isn't particularly expensive
I bought one but never got around to using it
When I was testing cells, I was using a west mountain radio CBA II, a few Ah meters, a few powersupplies and a couple of 12v loads I had floating around.
A real PITA - the imax would probably be better, but can't say till we try it
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
This also works fine
I did find that if I charged faster than 2A that once all cells had reached full the compression straps would fail - after it happened about 3 or 4 times I backed off to 1A
I did find the remaining good cells in a battery also had memory effect, probably due to being continually short cycled. so a full cycle is well worthwhile
when rebuilding the battery it is worthwhile starting with all cells fully discharged (less than 1v resting)
these nimh batteries have higher self discharge when at higher state of charge, so unless you test all cells simultaneously, you're better off starting with them flat.
The other bonus is the fuel guage also starts at 0 - particularly useful when using The Laird's nimh firmware
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
The biggest time consumer is the discharging part, because those small chargers only discharge at around 1A max. However, it is really a maximum wattage, not current, that limits the discharge current, so that the discharge current is much lower than 1A if you discharge multiple cells in series.
A CBA3 is much more suitable if discharging is required.
Testing the batteries in more detail ,so that you know the capacity of all cells as well as their self-discharge rate, will allow you to place marginal cells into the top layer of the battery, where they are easily accessible for checking and/or replacement later on.
I'm not so sure if low capacity cells always have high self-discharge rates. If you only test open voltage ( = not under load) after a 2 week period, then you might include cells into your battery that have low self-discharge, but also low capacity.
The definitive test to do is a capacity test after a self-discharge period of several weeks.
The charger I would use is the SkyRC Quattro. It does 4 batteries simultaneously.
Instead of buying a CBA3, you could build an inexpensive load that does a pack of 8 or nine cells at a time. 12V Halogen globes are perfect for this purpose. Each 50W halogen globe will waste 50W/12V = 4.1A into heat and light when connected to 12V.
V/I=R --> 12V/4.1A= 3ohm at the temperature reached under 12V.
For a 9 x 1.2V = 10.8V NiMH battery you get a bit more than V/R=I --> 10.8V/3ohm = >3.6A current drain per globe, because it will not get as hot under lower voltage and it's resistance will be lower than that of a hot globe.
For an 8-cell pack: 8*1.2V = 9.6V --> 9.6V / 3ohm = >3.2A .
Therefore, the current drain for a 8-cell module will be about 10% lower than for a 9-cell module if you use the same halogen globe array.
You will need to watch each modules discharge, so make the load big enough to make it a fast process. A 30A load will be within the specs for the battery and discharge the modules within less than one hour, so you could complete the test within a day.
What you need is about 2-3 metres of thick cable, rated for 30A or more, 10 Halogen globes, two crimped-on or soldered connectors for the cable ends (to bolt them to the cell connectors) and a wooden board or something like it to tie the cables to. Holes drilled through the wood allow you to tie the cables on with cable ties. Cables thick enough for the job will be spaced about right when next to each other so that you can just poke the sharp ends of the halogen globes into the cables. Poke as many halogen globes into the cables as you need to get the current drain you want. If you use 9 globes for 9-cell packs and 10 globes for 8-cell packs, then the results should be roughly comparable.
The result you measure is the time required to discharge the cells, so you also need a multimeter or voltmeter to check.
30A for one hour = 30Ah capacity. If yo are lucky and the cells have 20Ah capacity left after self-discharge for several weeks, then each test will take about 45min to do.
Once the first cell in a pack is empty, it's voltage will reverse and it's time to stop the discharge. You will see the halogen lights dim quite a bit when the voltage drops.
Summary of my suggested procedure:
- visual inspection: remove swollen cells.
- recombine remaining cells into 8 and 9-cell modules (compressed).
- charge at 1-2A under compression until full.
- let sit for several weeks to allow self-discharge.
- measure open voltages, remove cells with marked open voltage drop due to self-discharge.
- combine remaining cells into 10 cell modules (not compressed), then discharge with halogen globe array at 30A to find the lowest capacity cells. You could remove the lowest capacity cell from each 10-pack if the first cell is empty very early, and then continue the test with less cells or put in a marginal cell to continue the test.
This information may be used entirely at your own risk.
There is always a way if there is no other way!
Yes Josh, the constant current charger that I recommended is the correct one. It is designed to run a string of LED’s at a constant current and this is the correct way to charge Ni-MH batteries.
Leaving the batteries for 2 weeks will identify the damaged cells because these will have a high internal discharge. These batteries are the damaged ones in your Vectrix and will quickly unbalance the 102 module battery pack. These damaged individual batteries give you the symptoms of reduced range, high battery temperature while charging and the Vectrix charger performing an equalisation charge all the time.
The Imax B charger is not a suitable charger for the Ni-MH batteries. It also cannot test the batteries in a way that will identify damaged batteries in a Vectrix Ni-MH battery pack.
The problem of testing Vectrix cells was discussed on “The Australian Electric Vehicle Association”.
Posted: 03 June 2013 at 7:52am
Hi Tom,
Testing of NiMh cells is a chore but you need to do this.
Swollen cells are obviously damaged. The other poor cells have either low Amp/hr capacity or high leakage current and self discharge.
To test capacity charge a string of cells at 1.5 amps for 30 hours. Then discharge the string of cells at 10 to 20 amps. Check each battery periodically until flat say 1.0 volts. Capacity of each cell is amps x hours.
To test for leakage. Charge a string of cells at 3.0 amps for 14 hours. Leave them to self discharge for 2 weeks. Cells that have the lowest end voltage have high leakage. I would consider a drop of 15% in voltage compared to the best cells in the test to be high leakage. These should not be used in your vehicle as they will cause the pack to become unbalanced and can cause damage to your good cells during charging.
Ni-Mh batteries like to be worked hard in a vehicle and charged often. They do store well and the batteries you buy that have not been used for years will not have deteriorated, though most will be flat. The 1.5 amp charge is an equalisation charge that you should do first to check capacity.
Reference : Cobber, Australian Electric Vehicle Association, June, 2013
http://forums.aeva.asn.au/forums/studentevs-daihatsu-conversion_topic3276_page4.html?KW=student
It is not so!
The Icharger has a constant current charge function.Current up to 10 amps.
With this device, you can check the internal resistance of the cells.
Icharger can count watts / hour, it is necessary if you want to know the capacity of the cell.
The heading of this thread is " Checking / repairing NiMH Batteries."
The Imax B8 charger is a control box. It cannot charger anything without a power supply to run it. Why not buy a constant current charger that costs $15, suitable to use with Vectrix Ni-MH batteries. The charger I described is built to power a string of LEDs and is constant current with the correct voltage range.
The issue with damaged Vectrix batteries is not due to high internal resistance. This is another issue that is lower down my list and does effects old batteries. This causes poor acceleration and limited range with high speed cruising. Measuring the internal resistance will not find the batteries that will be a problem in the pack. Please read back through the post for issues in the Vectrix battery pack caused by damaged batteries. The way to test damaged Vectrix Ni-MH batteries is by testing for high self discharge rather than counting watt/hours. Previously overheated and damaged batteries have high internal chemical side reactions that cause high self discharge. If you test the battery immediately after charging with the watt/hour discharge count of the Imax8 charger you will not detect the faulty batteries.
It requires tests that can be done with other test equipment as explained. The Imax8 charger is better suited to charging Multi cell LiPo battery packs with a balance lead and then testing these packs. I will admit that this charger has a constant current mode and NiMH is mentioned in its specs, as mentioned in my post. Why not buy a complete charger than the Imax8 and a power supply.
I agree, in my NiMH battery pack the bad cells would not have been identified by IR testing (except when almost completely discharged).
See http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=6277&sid=f7722ec3f3720cfa381b7a58c4f02f16&start=25#p116761 for details.
Mik
This information may be used entirely at your own risk.
There is always a way if there is no other way!