Need a Recommendation for a Battery System (Hybrid Vehicle)

[Mike99]

Hello everyone,

I am working on a project to design and build a small hybrid vehicle.
The design will be to run two PERM PMG 132 electric motors
with the followings specifications:
1) 72 volts
2) Maximum current of 400A (continuous current of 220A) - 200A peak
current per motor (110A continuous current per motor).
3) Be able to run at maximum power (72V and 400A) for at least 10 seconds.
4) Weight is of concern (preferably under 50lbs)
5) Cost is of concern as well (Preferably under $2000)

I have been searching for a battery system that can satisfy these needs but it is difficult to find batteries that can discharge at this rate.

Could anyone recommend a battery system (or combination) that would be able to satisfy the above requirements?

I have been looking into NiMH and have been leaning towards this chemistry as it seems to be the simplest and cheapest.
Has anyone had any success using small NiMH cells in series (such as hobby D cells) to power high power motors? Or does anyone know of other suppliers that have high discharge NiMH batteries?

Or could Lithium based batteries be the only solution here. (I'd prefer to stay away from these due to the cost and need for a BMS system - which would be required).

Thanks in advance for any replies,

Mike

 

[AussieJester]

Or could Lithium based batteries be the only solution here. (I'd prefer to stay away from these due to the cost and need for a BMS system - which would be required).

I would say so, Nano Tech Lipo would be my suggestion, no onboard BMS required.

KiM

 

[dogman dan]

I agree. 10 seconds sounds like a drag strip. So you don't need capacity so much as abilty to deliver amps. For a bigger pack for longer duration, then cheaper lipo would work. So a small pack of expensive lipo may be cheaper for you than a big pack of cheap lipo, and obviously be less weight.

20 cells in series is nominally 72v, so perhaps 8 5s 5 ah lipo in the 90c nano type. 2 paralleled, then 4 of the pairs series connected. 900 amps theoretically, so 400 amps burst oughta be there with not so much sag. No bms, just have some simple lvc alarms on each paralelled pair.

Just 4 of em would theroretcally do the trick, but my experience says that doubling the ah to 10 will be worth it, and possibly even more size would lessen sag under those kinds of loads.

 

[Mike99]

Thanks for the replies,

Just a couple questions.
1) I have been reading that LiPo batteries can only be operated at high temperature (around 80C). Is this true for this type of battery?

2) I am also just confused as to why these batteries are so cheap. What is the disadvantage of using these batteries as opposed to the high end batteries non-hobby batteries that can be purchased from A123, Lithium Tech, etc...

3) Also the 5s rating on the battery concerns me, would this battery be more appropriate. Running 4 together (2S + 2P)?
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=14617

Thanks.

 

[Jeremy Harris]

Thanks for the replies,

Just a couple questions.
1) I have been reading that LiPo batteries can only be operated at high temperature (around 80C). Is this true for this type of battery?

Absolutely not for all common flavours of LiPo. The RC folk used to seriously risk life and limb by doing this, to reduce the cell internal resistance, but it's bloody dangerous and condemned by all the cell manufacturers.

2) I am also just confused as to why these batteries are so cheap. What is the disadvantage of using these batteries as opposed to the high end batteries non-hobby batteries that can be purchased from A123, Lithium Tech, etc...

They are cheap because they are supplied in large quantities to the RC model market, a market that demands high discharge rates and light weight. Their disadvantage over LiFePO4 cells is a shorter cycle life. If you're after very long cycle life then good quality LiFePO4 would probably better suit your requirement, but they will be bigger and heavier. Also, it's worth bearing in mind that cycle life for any lithium chemistry cell type is highly dependent on depth of charge/discharge. Cycling any of them between 0% and 100% will shorten their life dramatically, just as cycling any of them from, say, 20% to 90% will increase it dramatically.

3) Also the 5s rating on the battery concerns me, would this battery be more appropriate. Running 4 together (2S + 2P)?
http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=14617

Thanks.

Why worry about pre-made packs of 5S? They are pre-made into packs of a bigger size, which means less interconnects and a more reliable, and more compact, pack. These packs have balance taps connected to each cell junction, so even the really big packs, like the 8S and 10S ones, can be properly balance charged at the cell level.

Jeremy

 

[trappermike]

Have you looked at the Golden Motors website? www.goldenmotor.com They list some large powerful controllers,several hundred amps,foot pedal,hand throttle,and some big LiFePO4 batteries. I don't know about the quality but I don't think the prices are too high,might be the type of stuff you're looking for...

 

[trappermike]

I agree on using the Li-Po batteries,very light,high discharge rate to get your 400amps output.
But cheap?,I would think you would want to use the 50C Li-Po cells,maybe a 10ah or 20ah pack,so you're not draining the cells so completely,and I don't think the 50C cells are that cheap. Pack ah also depends on how far you plan to drive this machine,
Still I think you can achieve your battery requirements with Li-Po easily within your budget limit.

 

[trappermike]

Did you look at Golden Motor website?
They have controllers, 48v-72v,300A model and 500A model,$385 - $466.

 

[cell_man]

A pack made from A123 26650s terminated into a pack by me could meet or at least come very close to your requirements. Drop me a PM or email if you want to discuss.

The pack I have in mind could also be charged at about 150A if required. It could deliver more than 400A discharge but I think a more concervative approach would keep the voltage sag reasonable operating at about 12.5C, no where near the rated 30C.

 

[Mike99]

Thanks for the replies.

Just want to double check something before I make the final purchase.

The design changed slightly and we are now using 2 Lynch LEMCO LEM-200-D127 Motors. 72VDC, 100A continous, 400A peak.

I was planning to run each motor with a bank of 4 37V 10S batteries shown below. (2 in series, 2 parallel)
http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14609

First is this sufficient for getting the most out of this motor in terms of peak power? And would this battery bank be able to run the motor at 0-100A loads for about 10min?

Last thing is I do need a BMS for this system. Could someone please direct me too a BMS system (under $1000) that could monitor 8 of these batteries?

Thank you!

 

[Hillhater]

The design changed slightly and we are now using 2 Lynch LEMCO LEM-200-D127 Motors. 72VDC, 100A continous, 400A peak.

I was planning to run each motor with a bank of 4 37V 10S batteries shown below. (2 in series, 2 parallel)
http://hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14609

First is this sufficient for getting the most out of this motor in terms of peak power? And would this battery bank be able to run the motor at 0-100A loads for about 10min?
!

Well its obvious that it could run the motor at "0" amps ( ???) for a fair time ..
..and it should be equally obvious that at 100amps continuous, those batteries wont last 10 mins

I find it odd that you are apparently deeply involved in such a project , yet you ( and presumably your colleges ) appear incapable of the most basic of calculations to determine the required battery power ?? :?

 

[Mike99]

Totally agree, I find it odd.

Were all mechanical engineers.

 

[Mike99]

And by 0-100A I mean inputting amperage over this range. How long would it take to discharge the battery completely?

I dont really trust my electrical knowledge but heres how I would calculate it.

I have a 74V battery bank at 10Ah (2 5000mAh in parallel)
Wh = 74V * 10aH * 0.8 (0.8 for 80% DOD)
= 592Wh = 2.13MJ

Power consumed = 72V * 50A (50A average current draw)
= 3600W or 3600J/s

2.13MJ/3600J/s = 9.86min of run time

This seems off though?????

 

[Hillhater]

This seems off though?????

why do you think that ?
Thats as close as you are going to get until you have an accurate idea of your actual power usage/ current consumption profile.
unless you know precisely what your power draw is, you cannot expect to calculate battery duration with any accuracy.
A.. " 50A average current draw" .... is very different to .." by 0-100A I mean inputting amperage over this range"

 

[Mike99]

Could anyone recommend a BMS system that could be used to monitor 8 of these batteries?

Thank you.

 

[number1cruncher]

Could anyone recommend a BMS system that could be used to monitor 8 of these batteries?

Thank you.

http://www.tppacks.com/products.asp?cat=26

This is GGoodrum's and Fecher's BMS

 

[Mike99]

Thanks for the recommendation cruncher.

I actually need a BMS that could attach all 8 battery modules and be able to monitor both voltage and temperature.

Anyone know where I could find this. Budget for such a system is under $750.

Thank you.