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 Post subject: Stay away from hobby batteries
 Post Posted: Wed Oct 06, 2010 12:49 pm 
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Joined: Sat May 01, 2010 9:10 am
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I have just been contacted by one of the Formula Hybrid teams with questions about Li-Ion batteries, and I would like to share with all of you the advice I gave them. I'll do so in 2 posts, as the topics are different.

I would like to strongly urge you to stay away from hobby batteries and cells: they are fine for model airplanes, but they perform terribly in HEV applications, because their internal resistance is too high. In particular cells from a very popular brand that you are very likely to encounter (I prefer not to name it here) have been used with quite unsatisfactory results in an EV by a client of ours. Remember: those cells are energy cells, not power cells. An HEV needs power from its electrical system. (The energy is coming from the gasoline.)

However, of course, if the electric portion of your HEV is just for show, and doesn't really have to do anything other than meet the letter of the Formula Hybrid rules, then you'll be fine with such low-performing batteries.

Also, please be aware that there are two types of BMS: distributed (a cell board mounted directly on each cell) and non-distributed (spaghetti wires from a central electronic assembly). If you buy a ready made battery (with 4 or more cells in a single enclosure), you can't use a distributed BMS, because there is no physical way to mount the cell boards on the cells that are buried inside the battery.

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Davide Andrea
Elithion.com


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 Post subject: Umm what?
 Post Posted: Fri Oct 15, 2010 1:00 am 
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Joined: Tue Oct 06, 2009 2:15 am
Posts: 21
I would just like to warn everyone that this information is bunk.

Hobby Cells are by far the cheapest way to get high quality powerful cells into your car. These batteries are made to run remote controlled helicopters that go from 100% to empty in 4 minutes.

I challenge you to find a better battery for the money than this one:

http://www.hobbycity.com/hobbyking/stor ... duct=11957


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 Post subject:
 Post Posted: Mon Oct 18, 2010 8:42 pm 
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Joined: Wed May 05, 2010 9:18 pm
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Location: San Jose State University
I agree that the low weight, price, size and increased energy, power more than outweigh the high resistance you get with the nanotechs, but I would not call them "high-quality powerful cells". There are several real quality cells that are made by legit american manufacturers (and they actually come with data sheets). Anyone care to share side-by-side tested data? Hopefully within a few weeks we can report on our nanotech vs. headway 38120.

On the overall, I would agree with njs that the competition (or representatives of it) shouldn't advise against a battery cell just because it has high internal resistance. In a lot of vehicle setups (including most that did well last year), priority for the HV system was reduced weight and increased power. If you can live with some inefficiency, LiPo cells offer both.


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 Post subject:
 Post Posted: Tue Oct 19, 2010 7:36 am 
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Joined: Tue May 16, 2006 11:34 am
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Location: Formula Hybrid Administration
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Note that unless a post is from "admin" or is indicated as being by a member of the rules committee, the post is not an official opinion.

We have several highly qualified contributors to this forum from academia and industry and many of them have served as judges. Their advice is not "official" but should be taken seriously. These folks might be judging your vehicle next May.

(I would also like to express my opinion that the response from njs was on the edge of being unacceptably rude.)

-Doug (Member, FH rules committee)


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 Post subject:
 Post Posted: Wed Oct 20, 2010 1:20 pm 
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I will repeat what I said. All of the information in the first post is made up. I am rude because the poster appears to be trying to sell more product by posting false information.

The cells I posted can output 45C continuous and 90C burst. The only way they can do this is because they have exceptionally low internal resistance. Otherwise they would catch on fire.

I'm sure UC Davis and BYU would scoff at the notion that their batteries are somehow inferior because they were originally designed for hobby applications. The Tesla Roadster's batteries were originally designed for laptops and they appear to be working just fine.

Edit: On headway, as far as I know the company selling them had a huge shakeup and is no longer answering questions from customers or offering replacements for defective cells. The cells were not very powerful in the first place (maybe 5-10C max) and were only nice because they were fairly cheap and offered screw in tabs to connect.


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 Post subject:
 Post Posted: Thu Oct 21, 2010 1:17 pm 
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Joined: Sat May 01, 2010 9:10 am
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Hello njs (sorry, I don't know your name, as there is no signature in your posts),

njs wrote:
I am rude because the poster appears to be trying to sell more product by posting false information.


I apologize for giving you the impression that we sell cells (we don't) or that we are in any way associated with any cell manufacturer or vendor (we are not).

I initially offered that advice because of reports from our clients regretting choosing to use cells from one of the most popular hobby battery brand; I wanted to caution the Formula Hybrid teams in the hope that will not have the same negative experience. However, as you tell us that that advice is "bunk", I retract my advice and apologize for giving it.

The advice I give to this group is completely intended to be in the interest of the group; In doing so, I go through pains to separate myself from any commercial interest, to the point that I have endorsed products from competitive BMS manufacturers, because I believe that they will offer the best value to the Formula Hybrid teams.

Again, I am sorry for appearing to have commercial interests when offering advice. I will try to be more careful in the future, and, of course, I welcome you to offer opposing views in this forum.

Respectfully,
Davide

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Davide Andrea
Elithion.com


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 Post subject:
 Post Posted: Thu Oct 21, 2010 1:47 pm 
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Can you point us to the battery they used? I'm sure using a 5 or 10C cheap knockoff will not yield great results. There are hundreds of different hobby batteries at numerous current ratings. 45C is higher than A123, Kokam, or any battery that I am aware of.

It may be important for teams to properly choose the type of hobby battery, but ignoring them entirely will lead to substandard results.

Also, does anyone think the original post was a bit rude?

"Your electrical system was just for show"

Comes off as flippant and condescending, especially considering how wrong the information above it was.


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 Post subject:
 Post Posted: Thu Oct 28, 2010 4:07 am 
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Joined: Wed Sep 12, 2007 5:22 am
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Location: NCTU MECE
njs:

I do have a different reason to speak against hobby batteries.

When you order hobby batteries, you are unlikely to be able to get that many batteries with similar internal resistance. (I assume somewhere around 100 cells are neede)

My LFP battery sponsor told me, in order to provide us with the 100 cells needed, they need to make 300 cells and measure them one by one, so they can match out the 100 cell pack for us.

I believe there would be some difficulty to do the same with hobby batteries.

But if you don't plan to charge them all in series, then problem don't exist.


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 Post subject:
 Post Posted: Fri Nov 05, 2010 4:40 pm 
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Joined: Tue Oct 06, 2009 2:15 am
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If you are using 100 batteries for your pack you are essentially using the same batteries as someone using hobby cells.

Placing cells of similar resistance in series and then paralleling these strings largely mitigates this fairly trivial problem.

It is still recommended to have some kind of cell level warning system no matter how closely your cells match.


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