Lithium Ion City El - What a difference!

[ChrisB]

I'd also like to hang on until lithium batteries become available that don't require the added complexity of a BMS.

You dont ACTUALLY need any BMS if you dont want to, and just use the good old fashion voltmeter and generally keep an eye on them.
Alan and Honer dont have any such thing in my Fiesta that has Li-ions fittted and they carry out all their BMS the manaul way by measuring volts on the cells and adjusting the charge rates accordingly and todate I dont think they have had any problems.
Of course it does mean you have to pay a lot more attention to the batteries, where as BMS is fit and forget.


ChrisB

[MalcolmB]

Of course it does mean you have to pay a lot more attention to the batteries, where as BMS is fit and forget

Thanks for that Chris, and thanks to Peter for the info from Agni Motors!

It sounds as if Cedric Lynch's controllers would make the best sense when I eventually switch to lithium. I guess I'm going to have to learn some basic electronics though, because I don't like fitting stuff if I don't know how it works.

[ChrisB]

Know what you mean, I think Cedrics BMS's are simple shunt affairs which once the battery reaches a preset voltage they simply shunt the charge current around that cell.

There must be a bit more to it than that mind you as once the whole pack has reached top charge then in theory the charger would be short circuited so there must be some sort of current limitation somewhere as well.

ChrisB

[EVguru]

Cedric's cell protectors have a low voltage detect. When you hit the low level they turn on an opto-isolator. The outputs of the optos are connected in parallel and if you have the common 0-5K throttle, simply connected accross it. Thus when you reach the low level on any cell, it throttles the controller back.

The high limit works a little differently. At the voltage limit an increasing load is placed on the cell to hold the voltage down. This provides a degree of bypassing and thus balancing of the cells. An opto-isolator is wired in parallel with the load and will turn on when the voltage across the load is about 3 volt. These optos are also wired in parallel and are connected to the chargers voltage control pot to 'throttle' the charger back.

If you have regen the high limit should also limit the regen current.

[aminorjourney]

The thing I like about the REAP monitoring kit is the fact that it is completely customizable. You can tell the unit what cell voltage to charge to as well as what should be considered a "low" voltage.

After the first full charge/discharge cycle the BMS works out exactly how many AH are in the cells and as a result the 'fuel' gauge arrangement is very accurate on the dash. You can also, as I have done, stipulate the minimum current that the batteries can provide before the system assumes the batteries are 'dead'. I've found this very useful. Living in Bristol there are lots of hills and lots of busy roads. I've set my unit so if the batteries can't supply more 70 Amps or more then the pack should be considered empty. After a few trips the gauge now knows when that will be (roughly, since it keeps a track of the energy going out and going in to the pack). It means that when my gauge is nearly empty I know I can still get home and can still climb hills

I think both systems are very good - it depends on what your specific needs are as to which you choose, or in fact, if you decide to not have protectors or perhaps do your own - as Alan Richmond has done with his Aixam conversion.

[ChrisB]

Cedric's cell protectors have a low voltage detect. When you hit the low level they turn on an opto-isolator. The outputs of the optos are connected in parallel and if you have the common 0-5K throttle, simply connected accross it. Thus when you reach the low level on any cell, it throttles the controller back.

The high limit works a little differently. At the voltage limit an increasing load is placed on the cell to hold the voltage down. This provides a degree of bypassing and thus balancing of the cells. An opto-isolator is wired in parallel with the load and will turn on when the voltage across the load is about 3 volt. These optos are also wired in parallel and are connected to the chargers voltage control pot to 'throttle' the charger back.

If you have regen the high limit should also limit the regen current.

Cheers for that Paul I did wonder how it worked, pretty simple really.

Do like Reaps system as well as it does seem very play'able with, mind you I think the cost difference is quite a bit ??

ChrisB

[Fufunka]

Hi, I think that the Thunder-sky parent company is nowadays offering a BMS system as well. But interestingly enough not very cheap either, roughly more than one $grand for 48V system, it sports a display/controll unit which is attached to another box and then to individual battery modules..

Also, wasn't Peter Perkins (SolarVan) working on his next gen Mark2 version of BMS for his TS battery pack?

[retepsnikrep]

Also, wasn't Peter Perkins (SolarVan) working on his next gen Mark2 version of BMS for his TS battery pack?

I was, but as necessity is the mother of invention, with Cedric's cell monitors in place, I haven't needed to do anything more with my BMS system.

Time is also a luxury I don't have much of at the moment.

Peter

[Fufunka]

That's a "sad" news I liked very much your integrated display concept - I've even dry tested that progie which you have made downloadable for it!