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This is part 1 of an advanced mod. It's dangerous working on the HV battery pack and associated components. Don't do it if you are not happy.

Grid charging has been done before in various forms, so thanks go to Mike Dabrowski, Armin Kusig and James Frye for their work in this area, which is still very much ongoing, I recommend you follow developments at Mike's site, especially with regard to pack balancing ;)

I decided to implement the grid charging and simple balancing mod on my two cars to pre-empt problems that may arise as the packs age, and to help with my wife's short 5 mile commute which hits the battery hard on a daily basis.

Safety first. I ensured pack was off before starting, and allowed capacitors to discharge on the controller. I checked voltages were safe with a meter and used the one hand technique with rubber gloves when fishing down between the battery pack and motor controller. It's a real tight squeeze with no room to maneuver :(

Having read the various posts an this site about grid charging, and the fact that a low current 300ma charge may also help re-balance a failing pack I opted for the simple series charger.

A 300ma series charge applied to the pack (overnight) should be safe for the cells for a limited period say <12-18hrs. As individual cells reach full charge they will start to warm up, but 300ma should be low enough not to cause any gassing or other problems. As all the cells reach full charge you eventually end up with a fully charged and balanced pack hopefully.

The main advantages I can see is you start the next day with a fully charged and balanced pack (probably slightly warm as well) allowing full assist from go.

For the project you need a simple safe way of connecting to the battery pack, and bringing this connection out to a socket which can be connected to a 175v 300ma approx constant current charger.

I wanted it to look as discrete/standard as possible, in fact you can hide the charging socket fairly easily ;)

It has to be very safe, for this reason I included 400v 3A diodes in the +/- charge leads adjacent to the pack connections so that the High voltage present could never appear at the socket or in fact outside the HV compartment. I lose a volt in the diode forward voltage drop but it's a small price to pay.

UK Insight's have a nice place above the rear number plate to mount a socket, it's fairly well protected from the weather and can be fitted with a sealing cap.

http://www.solarvan.co.uk/insight/chargingproj01.jpg
http://www.solarvan.co.uk/insight/chargingproj02.jpg

I used a 3 pin 3A 250v connector and 6amp 3 core arctic flexible cable for the project.

http://www.solarvan.co.uk/insight/chargingproj03.jpg
http://www.solarvan.co.uk/insight/chargingproj04.jpg

I routed the cable through the blanking grommet in the rear panel around the right hand side into the hv compartment. Cable ties etc to keep it all neat and safe.

http://www.solarvan.co.uk/insight/chargingproj06.jpg

The cable eventually is threaded through until it is between the HV battery pack and the motor controller. This is where it gets tricky :( The lack of room means you can't easily connect to the + side of the pack in situ.

See Mike's labelled diagram.

http://www.solarvan.co.uk/insight/chargingproj12.jpg

You can't get at that nice screw he has arrowed on the + side without removing the battery pack :( Well I couldn't anyway. However you can get to the other end of that orange wire, which is fitted with a 6.4mm 1/4 standard spade connector and connects to one side of the pre-charge resistor.

http://www.solarvan.co.uk/insight/chargingproj05.jpg
http://www.solarvan.co.uk/insight/chargingproj13.jpg

Basically I piggy backed onto here and used one of those 'Lucar' spade double adaptors to connect. It's difficult to get in here with big hands and remove and re-connect the spades, but it can be done, be careful of the pre-charge resistor, the terminal is quite weak and will bend, as will it's mounting if you use too much force.

http://www.solarvan.co.uk/insight/chargingproj14.jpg
http://www.solarvan.co.uk/insight/chargingproj07.jpg
http://www.solarvan.co.uk/insight/chargingproj08.jpg

The - terminal is easy as it sits atop the pack, and is the main negative lead. Note the diodes in my wires close to the pack to prevent voltage flowing back to socket.

http://www.solarvan.co.uk/insight/chargingproj09.jpg

I also connected the earth wire to the earth point on the controller case which is connected to the vehicle chassis.

http://www.solarvan.co.uk/insight/chargingproj10.jpg

Now I put it all back together again, double checked the connections, tested the diodes and continuity to the socket and threw the main switch.

Tested socket and no voltage present :)

http://www.solarvan.co.uk/insight/chargingproj11.jpg

Last photo for part 1 shows socket with plug installed. I am now waiting for a few more components to arrive, including my nice psu and I'll start on the charger side. Hopefully next week.

I'll update asap. Peter
 

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YES! please keep us advised on this project. i would love to be able to grid charge my pack.
 

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300mA should not cause the battery pack to produce any significant heat build up or warm up... At most I would expect about 1 or 2 degrees above ambient.

After you have charged up the car's battery Pack over night... Expect the Insight to do a positive recall as you have changed the SoC and Voltage since the last point in its memory.... so you should not expect to see any assist when you first start the car....

After the positive recall you will have your fully charged and usable battery ....

remember not to over charge the battery pack... after a while ( 2 hours or so ) of rest from being disconnected from the charging current the pack should read under 170V...

Also remember that by doing this you are doing a full 100% SoC... and not the cars normal 80% SoC top end.... so after about ~500 cycles of doing this you will have lost about 10 to 20% of the total capacity of your battery pack permanently.... after another ~500 cycles you will loose another 10 to 20% etc...etc... until your pack is gone.... Honda limits the SoC to above 20% and under 80% in order to get about ~5,000 Cycles per 10 to 20% loss of capacity.... The Prius limits even more to try to extend the battery packs life even more.... Voltage of a NiMH cell will only tell you if you are in the top and bottom 10 to 20% SoC, Voltage will not tell you anything useful about the middle 60 to 80% SoC...

The Only way to avoid the positive recall is to have the cars systems on while you are charging it so it can track the charge...

That would require more current than 300mA in order to keep up with power all the vehicle systems.... even though you do not want more than 300mA going into the battery pack uncontrolled.

If the vehicles systems are powered on you might get an error code if the car detects a ground connection on your charging system ... or if it checks for a 0V condition and you are feeding it a charging current at that time...

Best of luck... keep us all in the loop.

... stay safe...
 

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Discussion Starter #4
Positive Recall

I should have mentioned positive recalls in my original post of course. Doh!

I won't be leaving the car on overnight to monitor the charge. The charging/balancing system is not something I expect to use all the time.

Once a week perhaps, to avoid a forced charge commute scenario.

I tend to know when it is going to throw a forced charge, basically I want to prempt that condition. As the battery falls I know when it is down to say 1/2 - 2/3rds, it's time for a boost.

I have also added the charge point to my second car now, so both Insight's just waiting for the PSU bits to arrive ;)
 

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IamIan said:
300mA should not cause the battery pack to produce any significant heat build up or warm up... At most I would expect about 1 or 2 degrees above ambient.
Actually, I found that 300mA causes significant heating, once the battery is full. Enough to make the cooling fan come on once the ignition is turned on after the charge.

To prevent that, I usually keep the cooling fan running on low speed (by connecting a 9V supply to it).
 

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Hi Peter,
Thats great that you grabbed the ball and are giving this a shot.
Next you need to build up a HV solar panel with the same plug.

1. the 300MA is a gentle charge compared to the 50A it can see when used, and we never are discharging to zero, which would be the other end of the "FULL CYCLE". Some degradation may be happening, but it should not be the 20% after 500 cycles
2. We did a 300ma test with the prius subpacks a week or so ago, and while the temp did not raise more than a degree, it was likely due to the subpacks being spread wide open and at 45F ambient, and my stopping the charge as soon as I was able to detect the internal pressure raising by a slight outward deflection of the cells flat walls. Can't say exactly at which point in the top of charge zone we were at, but I estimate it was near full.

3. While the two diodes should be sufficient, I will likely place a fuse rated for 200 VDC, 1A in the charge line near one of the pack connections as well as the diodes just as an additional safety, as diodes can short.

4. Based on Armins feedback about the batteries temp, You may want to play with using the PTC band resistance as an additional end of charge detection. The PTC strip is in contact with all cells, is brought up to the BCM, and has a relatively sharp resistance raise when the temp gets over 100F. A single subpack PTC will measure about 1.5 ohm cold, and when heated to ~120F was about 20 ohms.

5. I have a digital voltmeter connected to the battery pack, that I can watch while driving. The max voltage under full regen is right at 179-180VDC, but it will drop back once the charge is removed to the 160-170V range, based on the true SOC. Temperature will change the voltage as well as charge current, so voltage is only useful for relitive SOC determination.

You really need to pull the pack to get on that lower screw with enough room to properly connect. I was thinking of using a spade adapter like you did on the precharge, as the easiest way to tap into the pack.
Keep us posted.

We need to remember that recals, and codes of death with pack replacement are happening on packs all the time, and those packs are supposedly kept in the 20% to 80% range.
Where are the 10K cycles on those packs?
 

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Discussion Starter #8
Balancing

Mike Dabrowski 2000 said:
Hi Peter,
Thats great that you grabbed the ball and are giving this a shot.
Next you need to build up a HV solar panel with the same plug.
I have one of these on my van!

Mike Dabrowski 2000 said:
1. the 300MA is a gentle charge compared to the 50A it can see when used, and we never are discharging to zero, which would be the other end of the "FULL CYCLE". Some degradation may be happening, but it should not be the 20% after 500 cycles
I agree, I don't think degredation will be as bad as IamIan thinks.


Mike Dabrowski 2000 said:
3. While the two diodes should be sufficient, I will likely place a fuse rated for 200 VDC, 1A in the charge line near one of the pack connections as well as the diodes just as an additional safety, as diodes can short.
I might put a 1A fuse near the socket, I don't want to have to open up the HV compartment if it blows :(


Mike Dabrowski 2000 said:
4. Based on Armins feedback about the batteries temp, You may want to play with using the PTC band resistance as an additional end of charge detection. The PTC strip is in contact with all cells, is brought up to the BCM, and has a relatively sharp resistance raise when the temp gets over 100F. A single subpack PTC will measure about 1.5 ohm cold, and when heated to ~120F was about 20 ohms.
I looked at this but don't intend doing anything with it initially.


Mike Dabrowski 2000 said:
We need to remember that recals, and codes of death with pack replacement are happening on packs all the time, and those packs are supposedly kept in the 20% to 80% range.
Where are the 10K cycles on those packs?
They are probably waiting to be balanced by a charge like ours, and then they would be ready for another 50,000 miles ;)
 

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Discussion Starter #10
Insight group dc power supply proposal.

As I am now working on this project the long term prospects of it have ben intriguing me. So I am going to pose a few questions! Assuming it works as we think it will of course ;)

1) Should we try to roll this project out in a simple mains powered form, so as many members as possible can take advantage of it?

If the answer to 1 is 'Yes' then we need to standardise a few ideas and equipment at a fairly early stage.

2) What voltage and charge current do members think is the most suitable for the long term overnight series balancing charge of our battery packs? I think the below specs are suitable for our project charger.

a) Regulated 175v dc output at 250ma constant current. (I like 1/4 of an amp it's a nice round number, and less likely to cause battery problems, but it's still enough to give a decent overnight boost.)

b) AC Mains input 50/60hz 115v/240v AC dual input, so suitable for worldwide use.

3) Should we investigate getting some psu's (Say 100) made up with the above specs from some psu company? (China?) Any ideas? Or does anyone know of a suitable psu brick? I appreciate it's fairly easy for a hobbyist like myself and some others on here to make a linear psu to the above specs, but I think we should try for a corporate approach with some proffesional and safe equipment :shock:

4) Should we go for switch mode (More effcient 90%) or Linear (Probably cheaper but only 70-80% effcient)?

5) What vehicle plug/socket combination should we choose to allow a bulk purchase to suit our project? Where should we put the socket/plug?

I am happy to act as the UK co-ordinator installer for this mod. If I can help UK Insight owners with failing packs and no warranty :( I will certainly try to do so once mine is up and running.

I am willing to put my money where my mouth is and subscribe $500 to help bankroll the initial cost of this project if we can locate/agree on specs and a suitable psu manufacturer.

Over to you 8)
 

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I vote yes to a plug-in kit for the masses and I'll commit to buying one.

I never thought a plug-in option would be of much use on an Insight since there's no fully electric running mode, but one of our Insights has past 200,000mi and the dealer's said no free battery this time. (they want $3500 installed) So if a plug-in kit could keep the batteries healthy it would be good ecologically and for the wallet.

-John
 

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The kit that remains unnamed is just crying for a plugin option, assuming the price is right I would be in for one also.

Now, as far as the psu, wouldn't it make more sense, and be safer if the psu was located in the car, and 115 / 220 was run in via a standard wall plug? The reasoning being the PSU would definitely isolate the high current DC being safer than diodes / fuses?
 

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Discussion Starter #13
Plugged into car for first time today

Plugged home made variable voltage constant current psu into car today for first time :shock: Charging at 250ma. IMA Battery was only one bar from top when I started anyway so will be interetsing to see if it lights up the last bar tomorrow after a positive recal.

Home made 0.5A Variac PSU awaiting some odd bits but working.

http://www.solarvan.co.uk/insight/chargingproj15.jpg

Car plugged in.

http://www.solarvan.co.uk/insight/chargingproj16.jpg

Charger is consuming 57watts from UK 240v AC Mains and delivering 250ma into battery at about 165v at present, that voltage should rise as battery approaches full charge but current should remain static at 250ma if my current limit is working!! I have been bench testing my charger with my old IMA pack over the last few days.

http://www.solarvan.co.uk/insight/chargingproj17.jpg
 

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Discussion Starter #14
uhtrinity said:
Now, as far as the psu, wouldn't it make more sense, and be safer if the psu was located in the car, and 115 / 220 was run in via a standard wall plug? The reasoning being the PSU would definitely isolate the high current DC being safer than diodes / fuses?
Possibly, but I have two cars and a spare IMA battery and don't want to buy/build two/three onboard chargers at the moment, also I don't really want to lug the charger weight around all the time even if it is only a pound or so.

If the charger weight can be kept right down then I accept that it is probably best if it is built into the HV compartment with a standard AC mains inlet to the outside world! We really need a fit and forget solution where you just plug it in overnight say once a week to get the benefit of an equalising low current charge. 8)
 

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I'm ready for grid charging. I have an 1800 ft elevation change within 14 miles up/35 miles down from my house and I'm routinely returning home with a low SOC. If I FAS down the hills and limit assist up, I can manage over 90 MPG ave until the forced charge begins, then its down to the 70's. If I depart the house with a low SOC to begin with and heading up the grade it's downright painfull, no assist and forced regen going up.

I'd be very interested in a charger as well, I searched the forum and couldn't find anything specific other than a variac circuit and multiple power supplies in series to come up wit the 175 vdc or so and .25 to .33a. I'd like to install an onboard charger so I can take advantage of 'opertunity charging' as well as I travel alot.

I'm not an electronics expert by any means but I remember making simple AC/DC converters for electronics class in college with half wave and bridge rectifiers. I found and dusted off my old notes from class and had written a half wave rectifier has ~45% of AC voltage and full wave ~90%. A voltage doubling rectifier has 1.8 times ac voltage but I did not have a circuit diagram drawn for this type. This got me thinking, 117vac (at my house) times 1.8 = 210 vdc. A simple resistor could be sized to limit current and serve as the ~35 volt drop. Of course it would include diodes and a fuse for protection and maybe a choke and/or capacitor for some 'smoothing'. Total cost for parts is maybe $25 with an enclosure, wire and connectors.

I know this would't be the most efficient charger but the resistive energy bleed is only 35vdc * .33a = 11.55 watts with over 57 watts applied to the batteries.

Anyone have any real world experience with this application?

Anything more specific on what you are using for a grid charger?
 

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Discussion Starter #16
I did get a quote for a 175vdc cc 250ma supply but it was over $100 and lot's of variables, I might follow it up again when I get time.

Although I have fitted both my cars with charging receptacles connected to the IMA pack for this project, my batteries are in good condition and I haven't needed to use any grid balancing/charging as yet. Necesssity being the mother of invention I haven't need to do it, so I haven't! :)
 

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noother said:
I'm not an electronics expert by any means...
Hi Noother,

sorry to burst your bubble, but you just disqualified yourself right there. Designing, building and installing your own grid charger (in a way that doesn't electrocute and/or incinerate you and/or your car) does require an electronics expert!

It's not as simple as hooking up a supply with the right voltage. You need a constant-current source to charge NiMH batteries. A resistor doesn't work for current limiting, because the battery voltage varies a lot. A variac or direct-rectified mains is a bad idea because it provides no isolation.

I'm afraid until someone comes up with an easy-to-install kit with instructions, grid-charging is limited to electronics geeks and suicidal maniacs! (luckily, I qualify on both counts :cool:
 

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OK, now were making some progress! Lets keep going.

retepsnikrep, I would gladly pay $100+ to not have to reinvent the wheel. More info would be awesome!

Variac= bad, why, how does the circuit work and interact with a charging battery?

Resistor= not current limiting? As a kid I used to race remote control cars and boats. I made my own charger with a simple resistor in series with an ammeter. This would charge a 7.2v, 1.2ah nicad in about 15 minutes from a 12v car battery. I'm pretty sure the resistor limited the current because I had to play with different resistors to get the current right and if I had hooked the 7.2v directly to the 12v there would have been alot of smoke! I ended up making it a dual charger by switching another resistor in parallel for more current. I then further modified it to trickle charge with a separate higher resistance circuit. It certainly was not constant current, the current would start high and taper off as the pack voltage rose. Simple ohms law stuff, even for an 11 year old. If I had an isolated, regulated 170 vdc power supply ran through an appropriate resistor to the pack, as the pack approached 170 volts current would taper off towards 0, more like a constant voltage charger, the resistor alows for voltage 'droop' and limits the current. I like this idea better than a contant current charger that, once charged, just keeps forcing the amps into the pack creating heat. Thoughts?

I have searched and read all I could find on this site about grid charging the pack and have taken extensive notes. Everything else is in place except for the charger.

I understand you take your chances in life, and you live with the consequences! Suicidal i'm not, but I have marine engineering degree, welding experience, 10 years working with 3-phase 480vac and 120 vdc systems, and a strong desire to learn and tweak things to make them 'better' for what I want them to do.

Armin, I appreciate your advice to steer me away from doing this. I'm am going to do it, with caution, and I will share my experience on the forum. If you think this information is too dangerous and don't want the info on the forum please PM me. I was hoping to learn from others on this forum so I can possibly avoid a bad experience if someone else has been down this road before. Isn't that the reason most of us are here?
 

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I'm getting closer to 'trying' a matching booster pack and have been thinking about ways to limit or cutoff plugin charging. One thing I had considered was using the ptc strips that are in the Insight packs to tell the charger when to stop charging. I would think that this could be used to get around the charging NiMH batteries in parallel , on top of that Insight packs should never hit peak charge anyhow which is at the heart of the parallel charging issue. Also as far as I can tell there are no issues with Discharging NiMH in parallel which I hope to test as soon as this weekend or early next week. Does anyone know how close the Pack voltages need to be for connection? I would hate to burn something out over a few millivolts difference.

For the record, when I did my subpack swap last week, I pulled the Insight pack at about 66% charge on the SOC guage, and all the batteries were at 7.89v +/- .02v, so there didn't seem to be any voltage imbalance issues.
I also drained them to 5.4volts using the Triton 2 and measured capacity as pulled from the car.

3 packs were between 1648 - 1729 maH
1 pack was at 2612 maH
4 packs were between 2303 - 2395 maH
The rest were between 1975 - 2283 maH

Currently I am doing a full charge for a 7.2V NiMH pack, with a cutoff voltage of 5.4v, and so far full capacity has been between 5711 maH - 5956 maH, and I started with the packs with the lowest and highest initial charge. This is by doing a full charge, and measuring the capacity on discharge. So far I have tested 9 subpacks this way.
 

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noother said:
Variac= bad, why, how does the circuit work and interact with a charging battery?
A Variac as I understand it, will vary the AC voltage which can then be rectified to DC... but as far as I know Variacs are ratio devices 50% of the Ac In = AC out or 200% of AC in = AC out... the voltage output will vary with the voltage input from the grid which can vary from about 110V to 130V.... some places are better or worse than others.... Also the Voltage output of a Variac I think is dependent on the current ... so as you drawl more or less current the voltage will also change.... As the Battery Voltage changes over charging the voltage difference between the Variac output and the batteries changes which results in a varying current load as well as varying voltage.

noother said:
Resistor= not current limiting? As a kid I used to race remote control cars and boats. I made my own charger with a simple resistor in series with an ammeter. This would charge a 7.2v, 1.2ah nicad in about 15 minutes from a 12v car battery. I'm pretty sure the resistor limited the current because I had to play with different resistors to get the current right and if I had hooked the 7.2v directly to the 12v there would have been alot of smoke! I ended up making it a dual charger by switching another resistor in parallel for more current. I then further modified it to trickle charge with a separate higher resistance circuit. It certainly was not constant current, the current would start high and taper off as the pack voltage rose. Simple ohms law stuff, even for an 11 year old. If I had an isolated, regulated 170 vdc power supply ran through an appropriate resistor to the pack, as the pack approached 170 volts current would taper off towards 0, more like a constant voltage charger, the resistor alows for voltage 'droop' and limits the current. I like this idea better than a contant current charger that, once charged, just keeps forcing the amps into the pack creating heat. Thoughts?
A resistor is another ratio device... it adds an amount of resistance that by ohms law will effect the output voltage and current... but as the voltage changes the current will change... as the current changes the voltage changes... Resistors also change their resistance as the temperature changes... when there is a 20V difference between the output and the battery a 1 ohm resistor will result in ~20 amps of flow... when there is a 10V difference the same 1 ohm resistor results in ~10Amps of current flow... thus it is a ratio device and will not prevent the current from going overly high or overly low.

In your example the resistor setup you had would only produce the current you wanted when the source voltage was a specific difference to the output voltage load.... when the grid voltage varies ~20V a simple resistor system will not compensate for this and will just dump more current and higher voltages into the battery.... including electrical surges and voltage spikes that could do instant permanent damage.

noother said:
I have searched and read all I could find on this site about grid charging the pack and have taken extensive notes. Everything else is in place except for the charger.
That i because the average consumer does not charge 120+D cell batteries all at one time.

NiMH:

NiMH batteries are best charged with a constant current device... Ideally the constant current you supply is in the safe charging range for the cell you are using... remember you have Oxygen , Hydrogen, and Electricity all inside a NiMH battery too much current and the cells will 'rupture'.... the dV/dT curve can be watched for the ~3mV bump that happens at end of charge... the temperature of each cell can be watched for the temperature generation bump that happens at the end of charge... the Voltage can be watched for a maximum upper limit as a fail safe... the number of Ah being pumped into the battery can be counted as a fail safe in case you over charge the battery.... if you use a constant current charger you can have a timed shut off as a simple means of Ah counting limiting... if the NiMH cells are in a flexible container like the plastic Prius cells are you can measure the volume increase of the cells that happens from the internal pressure increase that happens at the end of charge.

While just pumping current into a NiMH battery can charge it and if you have a upper limit voltage cut-off system you can have a simple battery charger... this method and the one you describe for the resistor battery charger you built... will be very hard on the batteries and you will end up getting fewer charge cycles out of them... that's all... if you are happy / ok with reducing the cycle life of the battery then use the simple resistor method...

NiMH battery charging is well documented on the net... search around and read up.

One last thing.... most people are tempted to try to use Voltage as a means of SoC determination for a NiMH battery... NiMH is different from Lead Acid... The Voltage of a NiMH battery will tell you when you are in the top 10~15% or so and the bottom 10~15% or so... the middle 70~80% SoC Voltage can NOT reliably be used to determine SoC for a NiMH battery....
 
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