[dtbaker]

I dunno if it is something in the water, or Rx for Lead poisoning, but my upgrade to lithium has brought a brand new EV grin.

Despite the ongoing legal battle with a-hole James Morrison on non-delivery of first pre-paid battery pack.... My new Thundersky upgrade completed yesterday is a HUGE grin over lead. Here's to hoping James gets whats coming to him!

Moving from 96v of lead to 120v of Li has been a treat!

30% more power and energy in pack for range in less than same physical space, dropping 500#.... been SWEEEEEEET. Moved from 'adequate' to really 'pretty good' performance, easier stering, wy better braking. Not in white zombie-land, but pretty darn good.

new pix and site update coming soon....

 

[carambo46]

great..... I will be using the crimpper u sold me soon, and get mine on the road
Car

 

[dtbaker]

loving it....

will report on balancing issues as time progresses, I decided to top-balance and go 'commando' with no BMS since I typically expect no more then about 50 % DOD. I will be VERY curious to see and report how the cells remain balanced.

 

[dtbaker]

not to worry... too much. I figure I have a pretty safe 50 mile range now, and typically do not exceed 20, so all should be safe at my ragged bottom end. )

 

[dtbaker]

I'm very comfortable that I am not anywhere NEAR the bottom knee using a typical 20/50 mile range... and very comfortable that I am at the upper 'knee' every time I charge. Hence very comfortable that in my case top-balance is the way to go... thanks.

 

[EVfun]

So Dan, how did you do your top balance? I'm about to top balance the 96 volt pack of Lithium cells going into the buggy.

 

[ruckus]

Congrats on the working car!!

I am wondering if there would be merit in finding the weakest cell, and then slapping a voltage meter on it. As long as that cell is happy, all others should be fine.

Has anybody tried that?

 

[Ektus]

Congrats on the working car!!

I am wondering if there would be merit in finding the weakest cell, and then slapping a voltage meter on it. As long as that cell is happy, all others should be fine.

Sure. But how do you ensure this cell will remain the weakest cell? Other cells may endure worse conditions (e.g. more heat due their location in the pack) and thus deteriorate faster.
I'd like to see a mini-BMS style system which measures the voltage of _each_ cell and can be monitored through an optical bus. Cheap digital multimeters with LCD display can be had for 5$/4€, including case and wires. Somebody should add an optical link, get the power from the cell it's measuring, and there you go. Local display of voltage as well as remote monitoring. But this discussion should go in an appropriate sub-forum, not the build thread.

With best regards
Ektus.

 

[Woodsmith]

I dunno if it is something in the water, or Rx for Lead poisoning, but my upgrade to lithium has brought a brand new EV grin.

You must be on the same thing as jackbauer!

I reckon lithium is going to be the 'high of choice'.

 

[dtbaker]

So Dan, how did you do your top balance? I'm about to top balance the 96 volt pack of Lithium cells going into the buggy.

I tried wiring in series and using my charger to dump in 'most' of the initial charge, as I suspected the pack was about 50% DOD on delivery... I was monitoring the kW in using my outlet kill-a-watt meter and figured I would have to add around 50% of the pack capacity. I started seeing cells taking off towards the end indicating the balance was off enough to notice. I tried manually draining the high ones with a big fat resistor, but had trouble getting things even, and got nervous about cell(s) taking off before I could measure during charge, so I unwired series and....


I wired the whole pack in parallel, connected to an inexpensive ($139) 10amp max. Mastech power supply set to 3.80v, and let it sit for two weeks.... amps in eventually dropped to zero. I took power supply out and let the pack sit in parallel for another week or so before un-wiring.

The power in... I hooked the + lead at one 'end' of the parallel block, and the - lead at the other just in case the voltage drop along the pack was an issue. I used the standard bus straps every other connection, and made some short connectors from 16ga lamp cord wire for the rest.

 

[Jimdear2]

Sure. But how do you ensure this cell will remain the weakest cell? Other cells may endure worse conditions (e.g. more heat due their location in the pack) and thus deteriorate faster.
I'd like to see a mini-BMS style system which measures the voltage of _each_ cell and can be monitored through an optical bus. Cheap digital multimeters with LCD display can be had for 5$/4€, including case and wires. Somebody should add an optical link, get the power from the cell it's measuring, and there you go. Local display of voltage as well as remote monitoring. But this discussion should go in an appropriate sub-forum, not the build thread.

With best regards
Ektus.

Ektus,

Just a quick repy on this subject. Look up a device called a Celllog8. It will monitor up to 8 batteries and will warn you of high and low voltages. About $15.00 USD each.
http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=10952

Jim

 

[dtbaker]

Ektus,

Just a quick repy on this subject. Look up a device called a Celllog8. It will monitor up to 8 batteries and will warn you of high and low voltages. About $15.00 USD each.
http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=10952

Jim

looks like a relatively low-cost way to easily monitor... but I want to wait a while to see if cells actually drift before I invest time and money wiring up a monitoring system.

I plan to check manually after a week, then monthly if all looks good, etc. If cell(s) start drifting out of balance too much at end of charge, then I may come back and wire in a monitoring system.

 

[Ektus]

Ektus,

Just a quick repy on this subject. Look up a device called a Celllog8. It will monitor up to 8 batteries and will warn you of high and low voltages. About $15.00 USD each.
http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=10952

Jim

Thanks, but that's not exactly the product I'm looking for. I'll elaborate in the BMS forum.

[edit]
There: http://www.diyelectriccar.com/forums/showpost.php?p=230189&postcount=34
[/edit]


Ektus.

 

[ruckus]

looks like a relatively low-cost way to easily monitor... but I want to wait a while to see if cells actually drift before I invest time and money wiring up a monitoring system.

I plan to check manually after a week, then monthly if all looks good, etc. If cell(s) start drifting out of balance too much at end of charge, then I may come back and wire in a monitoring system.

The proof is right in Jack Riccard's cell voltages. After a few months they varied by 17%. (not counting the first 10 which were used as a power supply)

I would think that the non-bms crowd would find their weakest cell and monitor it. If it is happy, all others will be too. Simple. No more guessing at the top or bottom. Every few months check to make sure it is still the weakest cell.

cheers.

 

[dtbaker]

I don't think this particular set of data has much to do with what I have.... a mixed bag of cells that were bottom balanced is completely opposite to my main concern which is having a top balanced pack to insure that all cells are close enough at the top to trigger the setpoint for the charger to switch from CA to CV and not have a HIGH cell go ballistic. I have almost no concern about the bottom because my typical use will only approach 50% DOD.

 

[ruckus]

This data applies to everyone, regardless of top or bottom balance.

The point is that OVER TIME, the cells vary by more than you would expect.

If you are happy to manually balance every couple of months over the life of the car, then it is not a concern, but that is an approach that will keep EV's from widespread acceptance. And every time you crack open the battery bank to measure voltages you expose yourself and the pack to catastrophic failure (like dropped screwdriver or melted wrist watch).

Oh sure, you are very careful, but what about the neighbor's kid who pokes into your garage, or a cat? It is better to keep the instant death sealed away for the life of the vehicle.

Again, monitoring the weakest cell might be a workable low-tech solution.

 

[EVfun]

I wired the whole pack in parallel, connected to an inexpensive ($139) 10amp max. Mastech power supply set to 3.80v, and let it sit for two weeks.... amps in eventually dropped to zero. I took power supply out and let the pack sit in parallel for another week or so before un-wiring.

The power in... I hooked the + lead at one 'end' of the parallel block, and the - lead at the other just in case the voltage drop along the pack was an issue. I used the standard bus straps every other connection, and made some short connectors from 16ga lamp cord wire for the rest.

Thanks for the explanation. It sounds very similar to what I had planned so it must be a good idea.

 

[dtbaker]

Thanks for the explanation. It sounds very similar to what I had planned so it must be a good idea.

or the blind leading the blind.


d

 

[ElectriCar]

Congrats DT! Mine arrived yesterday. Now I've got to get the racks built. Actually this time I'm going to build insulated heated boxes to better control temps.