Grid/Mains charging/balancing pack project

[retepsnikrep]

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

[HafNHaf]

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

[IamIan]

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...

[retepsnikrep]

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

[Armin]

Originally Posted by IamIan

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).

[retepsnikrep]

Armin

What output voltage is your PSU? Charge voltage?

What do you consider the voltage to be of a fully charged pack?

Peter

[Mike Dabrowski 2000]

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?

[retepsnikrep]

Originally Posted by Mike Dabrowski 2000

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!

Originally Posted by Mike Dabrowski 2000

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.

Originally Posted by Mike Dabrowski 2000

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

Originally Posted by Mike Dabrowski 2000

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.

Originally Posted by Mike Dabrowski 2000

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

[Mike Dabrowski 2000]

Wouldn't that be nice. This makes me wonder if my 2000 with 120K with a record of never having a recal may be due to my bumping the SOC to near the top every few days with MIMA.
Guess we will have to wait till we get some more experience with the grid charge procedure, and see if recal behavior changes

[retepsnikrep]

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

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