Experiment with li- poly batteries in a greenpower racecar

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hohisilver
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Re: Experiment with li- poly batteries in a greenpower racec

Postby hohisilver » Thu Feb 10, 2011 7:18 pm

Jeremy:

My charger is cheap and simple, but is for the lower voltage requirements of LiFePO4. I use some cheap (search eBay) DC DC converters. They have isolated inputs and outputs, so can be connected to a common power supply and still hook up via a multipole connector to the battery pack.


I'm intrigued by this idea for charging multiple LiFePO4 cells, and I think I have found some of these on eBay (although they are a little more expensive than when you bought yours). They specify 48V/2A input, so I assume this will be the current demand during the early phases of charging? This being the case, I guess I would need a pretty hefty PSU to drive more than 3 or 4 of them?
Ian.

A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....

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retepsnikrep
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Re: Experiment with li- poly batteries in a greenpower racec

Postby retepsnikrep » Fri Feb 11, 2011 8:29 am

Just chiping in on the original topic. I've modified my Honda Insight project car to achieve a near doubling of the IMA motor output power from 10kw to nigh on 20kw at present. It makes an enormous difference to acceleration and low end torque, so I thoroughly recommend so some sort of EV boost. It's my future trackday car and will surprise quite a few. 8)

I achieved a reliable 20%+ increase in current to around 120A and have run with the system voltage of uopped to over 200V from 60 lifepo4 cells.

I'm seriously looking at a pack of super nanotech type lipo now to squeeze every last drop of voltage and staying power into the stock Honda battery case.

With around 220V of lipo and at least 20A capacity i envisage less voltage sag (higher power) and a possible 25kw if the motor can stand it. :shock:

I have to be careful of the PM motor demagnetisation issue and heat but the duty cycle is very low especially in road use as i am in licence losing territory in a few seocnds. :wink: The stock Honda electronics seems quite happy with both raised voltage and current.

We intend to try the mods in the UK CVT Insight Lithium rally car in next few weeks 8)

Please keep us updated with your lipo work.
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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Jeremy
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Re: Experiment with li- poly batteries in a greenpower racec

Postby Jeremy » Fri Feb 11, 2011 11:34 am

hohisilver wrote:Jeremy:

My charger is cheap and simple, but is for the lower voltage requirements of LiFePO4. I use some cheap (search eBay) DC DC converters. They have isolated inputs and outputs, so can be connected to a common power supply and still hook up via a multipole connector to the battery pack.


I'm intrigued by this idea for charging multiple LiFePO4 cells, and I think I have found some of these on eBay (although they are a little more expensive than when you bought yours). They specify 48V/2A input, so I assume this will be the current demand during the early phases of charging? This being the case, I guess I would need a pretty hefty PSU to drive more than 3 or 4 of them?


Here's a link to my latest version of this type of charger, this time for charger LiPo (I've switched battery types to get better perfromance at lower cost): http://endless-sphere.com/forums/viewto ... Po+charger

I used some cheap 5V DC DC converters that I bought from Israel that can be trimmed down to 4.2V for charging LiPo. They are powered by two 500W, 50V power supplies I bought on eBay for £12.99 each, so not too expensive!

The input current to the DC DC converters I've used is quite low, as they are around 90% efficient. In practice they charge at around 8A, with an input current of just over an amp or so each, well within the total current I can draw from the power supplies I have (the power supplies can provide around 20A in total).

My LiFePO4 charger used 3.3V DC DC converters trimmed up to 3.63V and that runs on a Meanwell switched mode power supply that cost around £30, again via eBay. If your DC DC converters are 48V 2A input then they sound like they are more powerful than the 50W ones I used. Mine draw less than an amp each, usually, but do run hot and need fan cooling.

Jeremy

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retepsnikrep
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Re: Experiment with li- poly batteries in a greenpower racec

Postby retepsnikrep » Sat Feb 12, 2011 4:56 am

Jeremy do you want a Farnell 55A 48V dc 3kw ac input supply to power your beast dc-dc chargers? PM me. :)
Regards Peter

Two MK1 Honda Insight's. One running 20ah A123 Lithium pack. One 8ah BetterBattery Nimh pack.
One HCH1 Civic Hybrid running 60ah A123 Lithium pack.

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hohisilver
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Re: Experiment with li- poly batteries in a greenpower racec

Postby hohisilver » Mon Feb 14, 2011 4:59 pm

These are the ones I was looking at:

http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT

Says 50W which is why I thought they might be the same ones. How many cells do you charge with this method - I'd be looking at something over 20 which is why I'm concerned about the size of the power supply?
Ian.

A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....

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Jeremy
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Re: Experiment with li- poly batteries in a greenpower racec

Postby Jeremy » Mon Feb 14, 2011 6:02 pm

I've dug out the datasheet for this converter (http://www.part-datasheets.com/cds/jw050f81.pdf) and it looks like it should work OK. There is a slight risk that it might not trim up enough, but the datasheet spec does say it'll go to 110%, so that would give you 3.63V, pretty much ideal for LiFePO4.

I have made one mistake when buying DC DC converters for a charger - I bought one batch that didn't trim up enough, even though the spec indicated that they should. However, these were a different make to those you've found and did have what might be called a somewhat difficult to interpret spec sheet.

My LiFePO4 charger is only for a 12S pack, but the LiPo charger is for a 15S pack. I'm running them both from the same power supply box now, a pair of 500W, 50V power supplies that came from eBay, here: http://cgi.ebay.co.uk/NEW-UNUSED-50V-DC ... 587e03d24d

So far I've not found that the power supplies have had any problems supplying enough current, although these particular supplies do need some tweaking to get them to turn on and regulate properly. Peter's big supply would run a pretty massive charger, though!

Jeremy

bobc
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Re: Experiment with li- poly batteries in a greenpower racec

Postby bobc » Wed Feb 16, 2011 12:08 am

Here's the charging system I've come up with for the car: basically a fair number of these boxes each of which will charge 6 single cells with 3A.
Each charger PCB is on an isolated secondary on the transformer, each has its own bridge rectifier. So I can wire 'em up any old way without causing smoke.
Each 1 cell charge board is based on TI's BQ24600 chip which flashes leds to tell you what it's up to (and when the charge current has tapered off & it has finished).
Each 'box' has a 100VA transformer & delivers about 75W peak into the batteries (plus some heating of rectifiers, hence the fan).
The 2nd gen board is now under test (it has 3 circuits on a PCB, & the bodged on cap done right + unreg Vout for the fan) - so far so good....
Only problem I'm having is hand soldering the BQ24600 - it's in the most ridiculous SMD package... it's a double curse, as I get older and my eyes get worse, components are getting smaller... I got the PCBs done by PCBtrain, I've learned my lesson re: home made PCBs & fine pitch SMD boards ;^)
Image
Image
If anyone's interested I can send schematic/gerbers/BOM


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