102 replies to this topic

[MalcolmB]

Curious now, you mention you've tried this setup in practice – what was the application?

I've done the range calculations based on similar conversions and already have a small lead pack that will give around 10 miles range – sufficient for testing at least. Lithium ion prices are starting to fall so it makes sense to build the car first and buy the batteries last. NiCads are pretty rugged like you say but the only way I know of getting big batteries would be to cannibalise an electric Citroen Berlingo, and prices for those have soared recently. The Prius packs are pretty small and hard to find.

[brightsparkz]

Check this out....

http://www.commutercars.com/

two motors, not sure if they are in parallel or series though.

I better get a move on on my electric mini project

[MalcolmB]

Hey brightsparkz, thought you must have electrocuted yourself. I was following your project until it all went quiet. The weather's getting warmer so you can get back in the garage now. Last one finished is a stinkin' oil guzzler

The Tango's a great machine, with all that power you can almost forgive it for being so pug ugly. I'll have to do some hunting around to see if it's wired in parallel or series... Thing is, with such a narrow track it hardly needs a differential.

Edited by MalcolmB, 06 February 2009 - 11:14 AM.

[bigmotherwhale]

i tried it on a rc car made with mechano, it steered crap in parallel but went fast, i dont recomend lithium ion batteries at ll they are too weak, they hold alot of Ah but their peak current capacity is far too low around 2C so you will need around 10 of them in parallel to get the same current as litium phosphate, or ni cad./ nimh people have had sucess but their life span is apauling in this aplication, the guy was using 5000 li ion laptop bateries to solve this problem.

prius battery packs are pretty small but should out do their lead acid equivalants, the good this is they should fit where the rear seats are, so if you start with one and keep adding them in parallel eventualy there will be enough, and something to sit on! ive seen prius packs for 300 dollars but nows not the best time to be getting stuff from america. maybee a trip to the breakers you might come across someone who doesnt know their worth.

[MalcolmB]

Meccano eh?

Discharge rates have improved considerably over the last few years. Lithium phosphate and lithium polymer are both forms of lithium ion battery. The best cells can comfortably deliver currents of 20C (in other words 20 times their rated capacity, so 200 amps from a 10 Ah cell). Cycle life hasn't been proven yet, but for good lithium phosphate, estimates range from 1500 full charge/discharge cycles upwards if cells are not overcharged or overdischarged.

[bigmotherwhale]

the main reason i would never use lithium polymer, is that they can catch fire and burn violently, if over loaded or exposed to water, and from experience with rc cars is that they are pathetic and no matter how many you pack in there is never enough. lithium phosphate however are excelent in all respects except there price.

Edited by bigmotherwhale, 07 February 2009 - 01:46 AM.

[rcbamm]

Just my two cents. I was just reading up on this thread and had to drop in.

Lithium Polymer would be the way to go because one, the price has gone DOWN alot the past 4 years and they are the best batteries out there for the RC world when in need of light weight and alot of power.

check out www.unitedhobbies.com. They have HUNDREDS of different RC Lithium polymer batteries they sell. Price ranges from $1-$400 a pack or cell. The batteries I use in my electric RC foam airplanes are currenty 360mah 3cell 11.1 20c Lipolys that I bought for under $7 bucks a piece! two years ago I was spending $30-$50 for a 350mah 3cell 20c pack.

Yes, Lithium polymers are dangerous if not taken care of or properly used. I have dealt with over 50 different lithium polymer battery packs since 2005 and have never EVER had one explode or catch fire. The only incidents I have had is swelling of the battery pack in mid flight with dramatic loss of power. I simply discarded the battery pack but have never ever had a explosion or fire. I'v only had my packs swell up because of abusing the battery pack. Even when I tried to make my old packs catch fire I couldn't do it, but recently within the past few months I have succesfully fried a Lithium Polymer pack by twisting the positive and negative wires together and it only had about a 5 second small flame and then alot of smoke.

In conclusion, if you want ultimate power to weight + size, you must go Lithium Polymer or Lithium Ion. In the RC world I know Lithium Polymer has alot more C rating then Lithium Ion but I havn't dealt with many Lithium Ions but I know they aren't as likely to catch on fire like Lipolys. There is a new battery out there I'v heard of called Lithium Manganese and supposedly they pack just as much punch as a lithium polyner but they will never explode, catch fire, or blow up by abusing them or over charging them. I'v heard a battery pack that can power a car can be charged in as little as 10 minutes fully charged!


I know for fact that I cannot get the same power out of a Ni-Cad or Ni-Mah that I would get out of a lithium Polymer for the size and weight. All the new hybrid electric cars like the Prius are running on Lithium Ions or Polymers because of their big capacity and amazing power in a small lightweight pack. I also know they put them in a exposion cantainer so if they ever did explode, the fire would be inside the cantainer the batteries are in and the heat and smoke would vent out in a safe manner. Shoot, they are using Lithium Polymers in full scale electric airplanes.



Ohyes, another thing. Like I said "if propperly used"

One thing people get discouraged about Lithium Polymers is simply because they usually over discharge them past their volted rating. I.E. a 360mah 3cell 11.1v Lithium Polymer pack charges up to 12.6 volts fully charged and CANNOT be discharged passed 11.1 volts, other wise you will damage the capacity of the battery pack if discharged say to like 8volts and will dramatically shorten the life time of the pack.

Edited by rcbamm, 07 February 2009 - 02:38 AM.

[bigmotherwhale]

sorry i have become confused here, as far as i know lithium polymer have a high discarge rate ushaly around 20C and are safe, these are ushaly lithium iron phosphate type (LiFePO4) as far as i know,

lithium ion which contain lithium metal have a typical discharge rate of 2C and are only ever used in high Ah low discharge aplications such as laptop batteries and they are put in parallell even then becuse of there low discharge rate. if you cut one open and shove it in water it releases hydrogen and often flame but saying that its no where near as dangerous as petrol. the ones im thinking of are sony energytec bateries, from experience they suck and will not power anything that draws significant current your better off with ni cad.

you are spot on, there is another type of lithium ion battery that contains Manganese called NMC but ive never seen them in the flesh, there supposed to discharge faster and have a higher Ah rating than LifePO4

the trouble is that without saying each battery chemistry it gets very confusing. LiCoO2, LiMnO2, LiFePO4, Li2FePO4F are all lithium ion batteries

yes they are cheaper but to get both of those motors to work im guessing expect at least 100 amps at 100v thats 10KW a reasonable amount of power to move a mini that would require 15x 36V 20Ah LifePO4 battery packs each costing around £200 a pack thats £3000 pounds of batteris! if i have anything wrong please re calculate as its very late. a couple of hundred quids worth of old nicads might be more cost effective. i found a source of dead 4.8 volt 4ah ones from emergency lighting that were suffering from internal crystaline growth, a pulse discharge from a car battery restored and i was able to power a small go kart from them.

[MalcolmB]

Hi everyone and a belated Happy New Year! It's been far too long since I started this thread, but I got a little sidetracked. Anyway, finally have a little progress to show, so a few photos first:

 mini_drive_parts.jpg   271.25K   50 downloads
 mini_subframe_1.jpg   385.13K   100 downloads
 mini_subframe_2.jpg   404.1K   99 downloads

This was just a trial fit of one of the two motors (affectionately known as "Righty"). It went well, with no unforeseen conflicts, which is unusual for me, though I will have to rotate the motor 60 degrees to avoid fouling the subframe with one of the terminals.

I'm going with 3/8" duplex chain drive for the time being, but the plan is to switch to belt drive if everything works out well. The Gates carbon belts and sprockets are bit too pricey to experiment with.

A 75x25mm rectangular section will go across the top of the subframe to stiffen everything up and provide a fixing point for the turnbuckles that will be used to adjust chain/belt tension.

I need to get some little machining jobs done next: boring out the motor sprockets and getting keyways cut, and turning the driven shafts so that they'll fit inside the CV cups. Very tempted to buy a small lathe and do it myself, as I know it would get plenty of use in the future.

[MalcolmB]

Spent most of the weekend tidying up the garage as there was barely room to swing a ferret. But I did manage to fit the cross-member and tack up the mounts for one of the turnbuckles for tensioning the chain.

There was some wobble in the driven sprocket when I tried spinning it in the bearings. I'm not sure whether this comes from the taper hub mounting or whether the platewheel itself is distorted, so I've asked a mate who has access to a measuring machine to check it out. I want this to run smooth as butter!
 P1020248.jpg   497.6K   32 downloads  P1020247.jpg   488.79K   35 downloads

[charie t]

I don't know how i have not seen this, but i was driving home the other day wondering about if an electric mini was possible.
Batteries were the only thing i was concerned about. What to use, where to get them, and how you could charge them
Really interested to see how this goes. Looks good so far

[MalcolmB]

Yes, batteries are probably the most difficult bit, and the most expensive. Regular lead acid (gel batteries) are no good unless you're happy with a range of 20 miles or less. The best currently available option is one of the lithium chemistries. The cheapest and easiest to build into a car-sized pack are Thundersky or CALB, though there are several other options available that are lighter/more powerful and more expensive.

Quite a few people buy their batteries direct from the Chinese supplier. The only outlet I know for the large cells in Europe is this one: http://www.ev-power....o4-cells-(3.2v) but I've not heard any feedback about this supplier yet.

I've not decided which batteries to use myself yet, but I've got a dozen old lead acid gel batteries for testing.

[jinjrich]

This is very inspiring, good luck with it.

[charie t]

What does the prius use? is that a viable swap?

[MalcolmB]

Thanks jinj!

What does the prius use? is that a viable swap?

It uses NimH, and because it's a hybrid it has a very small pack. You would need a lot of them to make up a pack big enough for a pure electric car.