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  #41  
Old 11-03-2008, 09:27 AM
Technologic Technologic is offline
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Default Re: Planning Lifepo4 battery order, who wants in?

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Originally Posted by david85 View Post
Yes I did actually, its in an earlier post. The price for the 90 Ah cells was $0.466 /watt hour (BMS included), so the 160Ah cells are still the better deal.
Have you received prices without BMS? that could infact be the reason for the watt hour difference (higher) for the 90AH cells.

Either way I might just get more 160ah cells to keep voltage where I want it if the base price without BMS is that smaller

Did you ever receive any more information of how the multiple cell charging system would work? since it's built into the charger how can you make it smaller for each cell?

Last edited by Technologic; 11-03-2008 at 09:30 AM.
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  #42  
Old 11-03-2008, 09:28 AM
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Default Re: Planning Lifepo4 battery order, who wants in?

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Yes I did actually, its in an earlier post. The price for the 90 Ah cells was $0.466 /watt hour (BMS included), so the 160Ah cells are still the better deal.
David,

Another thanks going your way for all the work and diligence on this. Perhaps I missed it, but are you quotes in CAD or USD?

This is getting exciting.

Regards,
Gary
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  #43  
Old 11-03-2008, 09:58 AM
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Default Re: Planning Lifepo4 battery order, who wants in?

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David,

Another thanks going your way for all the work and diligence on this. Perhaps I missed it, but are you quotes in CAD or USD?

This is getting exciting.

Regards,
Gary

All prices are in US$ Last I checked our dollar was on the rise again, but I'll have to check again to see where it is (haven't checked today though). I'd like to make my order sooner rather than later.
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  #44  
Old 11-03-2008, 12:48 PM
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Default Re: Planning Lifepo4 battery order, who wants in?

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Originally Posted by Technologic View Post
This is unfortunate.

BMS's without low voltage cutoffs and high voltage cutoffs for each cell are dangerous.

that BMS may be better for just 1 cell... but you're planning 48... I'd seriously reconsider.

Looks like my plan to have an EE friend in college design a custom BMS is still the only option.
Technologic,

Check out this link and tell me what you think. Myself and RKM have had discussions with Darius at Electrocraft. He appears to be a very capable fellow and has built what you are talking about. This page has a cartoon of his BMS for LiFePo's. Notice it includes monitoring of each cell, over and under voltage and temp protection as well as collected and reported data and alarming. http://pages.interlog.com/~dgv/battery.html

Gary
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  #45  
Old 11-03-2008, 01:19 PM
Technologic Technologic is offline
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Default Re: Planning Lifepo4 battery order, who wants in?

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Technologic,

Check out this link and tell me what you think. Myself and RKM have had discussions with Darius at Electrocraft. He appears to be a very capable fellow and has built what you are talking about. This page has a cartoon of his BMS for LiFePo's. Notice it includes monitoring of each cell, over and under voltage and temp protection as well as collected and reported data and alarming. http://pages.interlog.com/~dgv/battery.html

Gary
There's a number of good things about that charging system. Firstly the resistor input for overcharging is a pretty great cheap idea to prevent overvoltage.

Secondly, though I don't like the marketablity of buzzers/alarms and totally shutting down charging if overvoltage occurs, but I do like the abilities here. These things could be applied to light systems, and tied to the charger to sort of "reset" any undervoltage limits once it's hooked up to charging again instead of manual push buttons.

In my opinion, the electronics should attempt to reset the cell digitally then restart charging if overvoltage of a cell occurs. Likewise with undervoltage it should simply "remove" that one cell from the group of batteries so it doesn't strand you... and it can then on the next charging cycle restart the battery system.
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  #46  
Old 11-03-2008, 02:18 PM
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Default Re: Planning Lifepo4 battery order, who wants in?

Electronics like this are well beyond my knowledge, but at this point I think its safe to say that it is possible to make a completely new BMS system if the charger mounted BMS is deemed to be unreliable or if you simply prefer the cell mounted BMS.

We'll have to see how this plays out, but at this point I'm ready to make my order unless theres something weird that I find out about the 160Ah cells. But if anything, they should be even easier to fit in the saturn. I'm thinking of going with 58 160Ah cells for a 185.6V system. Considering the potential savings and higher system voltage, a brushless motor will be used instead of a series wound brushed. The cost of this EV will have to be mostly spent before the end of the year to get the best tax write off for the business, so I can't wait too much longer.

The testing on my sample isn't finished yet, but we're prepared to take the risk based on what I know so far. It will turn over my diesel truck like nobody's business, and thats about the toughest test I can make anyway. I'll still try and take some measurements as time permits but my mind is pretty much made up.

Just waiting on Emily to get back to me with that info.....
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  #47  
Old 11-03-2008, 02:27 PM
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Default Re: Planning Lifepo4 battery order, who wants in?

Do you have a specific brushless motor in mind?
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  #48  
Old 11-03-2008, 03:00 PM
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Default Re: Planning Lifepo4 battery order, who wants in?

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Do you have a specific brushless motor in mind?
I was thinking of the MES 250 motor that metric mind carries, but not decided yet. I have a lead on what could be a better one, but I'll have to see. Azure is also said to be working on some better motors, not sure if they'll talk to me though.

Anything with 30HP+ constant and 100HP+ peak power and at least 5000 RPM will be good enough for me. Also expect regen considering the higher price. If worst comes to worst I'll could still go with a warp 9" or something like it.
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  #49  
Old 11-03-2008, 03:30 PM
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Default Re: Planning Lifepo4 battery order, who wants in?

How much would a 72 v 50 or 60 AH pack cost?
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  #50  
Old 11-03-2008, 03:56 PM
Technologic Technologic is offline
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Default Re: Planning Lifepo4 battery order, who wants in?

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Originally Posted by david85 View Post

The testing on my sample isn't finished yet, but we're prepared to take the risk based on what I know so far. It will turn over my diesel truck like nobody's business, and thats about the toughest test I can make anyway. I'll still try and take some measurements as time permits but my mind is pretty much made up.

Just waiting on Emily to get back to me with that info.....
That's fine mate... no issues with me... I'd just rather not have the BMS at all and save the costs :P
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