A123 System batteries

[billr]

I thought I'd start a fresh topic, instead of wearing out Bill J's SP blog update...
1st off, thanks to Bill J. for the idea to use a LiFePO4 batt pack.
I've looked at my RC packs, then at the bike, then at the battery...
I use stick packs, so I didn't see a good way to mount them.

Searching for a way to charge the battery on the bike.

...just need a basic circuit to do the cut-off.

I found this thread on RC Groups:
DIY charge cut out for A123 batteries
First post in the thread:

This is a DIY adjustable charge cut out device intended to be used with A123 battery packs. It can be used with Lipo chargers, nicad chargers, or a voltage source and current limiting. It's range is from about 9 volts to about 25 volts, so it can be used with A123 packs from 3 cells to 6 cells. It has been tested to 20 amps. A heat sink will be needed for the FET for high charge currents (over about 5 amps). The device will turn on as soon as a battery pack is connected as long as the pack voltage is under the cut out voltage. When the pack voltage reaches the set cut out voltage, the pack is disconnected from the charger. If the pack voltage drops far enough, the device will turn back on. The LED is on when the device is turned on, so the battery is being charged. "

This is exactly what I wanted to find. Auto cut-off and restart as the pack voltage changes.
There are schematics for the boards and part numbers for the elcetronic parts needed.
Hoo boy, more toys to make
Bill R

[cat]

yeayh!! Well done!! Thanks! Progress continues! ..next step, take the list to local electronics shop.

[DAVID THOMPSON]

i down loaded the link and made a pdf of the text and electrical drawing
in case the link disappears
i did not get to neat of a job of it but at least the basic info is there
DAVE
the parts list has some numbers that may be hard to find in the usa

[cat]

Good! Did you put all the big pics in it?

I downloaded all the big pics.
Components availability...can be a bit of a problem. Those guys did have a few issues. I hope my local supplier can get them all, find equivalents.

Some thoughts after reading it last night...

-- The heat sink. Some of those heat sinks those guys used are big - too big; we need the device to be encapsulated in the battery pack, we don't want any extra wires around. But apparently we would need only a small heat sink, or maybe no heat sink.
Need to fit the components closer together, on a smaller piece of board.

-- The potentiometer...to adjust volts / cut-off point. We dont need that, we're only using it for 14.4 V (4 x 3.6V). So need to ask him, what resistor can we use instead of the potentiometer. Or we need it to adjust the device to 14.4 cut-off and leave it there. But it adds another 10mm to the size. As it is, this device increases the size of the pack a bit. Although that's no problem, it's more of a problem to package it, the 4 cells with this thing attached; not as neat as just shrinkwrapping 4 x A123 cells.

[Old Dog]

I admit I am no electrical wizz but given that Bill J has this pack already fitted, what is the value add of all these components? Apart from being able to do it - why would one bother?

I can understand Bill J, he is on a mission (racing etc) so weight matters but for the rest of us mere mortal?????

[cat]

It's something I and a friend of mine have been interested in for a while.
Size/space and then the weight. (For my friend, that's important, because he's custom building an old Ducati...he'd thought of various places to put the battery. This is so small, it makes it simple.)

However, the self-discharge rate of the A123 cells is very low. Going by mine, it seems they discharged from 3.6V down to around 3.37 - going by what I saw as I started the charger on each of 3 cells. So, if we estimate it to be loss of 0.3V over more than a year (I mean lying in the cupboard), that would be about 1.2 V from our pack of 4 cells. So let's say our 14.4 V is down to about 13 V , 13.1 V or so. So leaving it standing for a few months without a battery tender, seems that it would be no problem. Even after a year, if it had dropped to 12.8 or 13V, that's probably still enough to run the starter motor ok.

The cost... the A123 cells, I don't remember what I paid for them but I could find the emails/paypal. Then these electronic components...on the RC forum, 2008, the one guy mentioned that it had cost less than $10, and that was for 2 of the devices. So it costs less than a new YUASA, certainly a lot less than a Hawker.
Anyway, I have the 10 batteries I bought for Maglite mods and 1-2 years later I still haven't got to using them.

PS: In Bill's case, the LiFePO4 / A123 pack he has either has a cut-off circuit integrated into it or - interesting - it doesn't, in which case the person making those is pretty sure they aren't going to be overcharged by a bike charging system.

[djsbriscoe]

Sorry I'm not convinced. I'll be sticking with my non leaking gell battery. Please read this

http://www.physicsforums.com/showthread.php?t=294828

and this

http://www.rcgroups.com/forums/showthread.php?t=209187

I have some concerns about the charging circuit needed to work with a motorcycle electrical system (the link to the schematic you posted is meant to connect to a "charger" which is not shown). LiPo batteries from what I've read so far need careful treatment and can explode. I know the circuit is designed to stop that but what controls the voltage between these limits and what provides the constant current needed?

Anyway I cant afford another battery and I don't need to save the weight.

David.

[cat]

I don't know that Bill J was advising everyone to use these alternative batteries.

Anyway. The page you linked is about LiPO. What we're doing is LiFePO4, quite different. LiFe does not burn. The risk or danger issues of LiPO are not applicable.
I learnt a bit about this, batteries and charging, when I was into hotting up torches a few years ago. A lot of reading, a lot of searching - a LOT - many hours, many nights, and so on, but I learnt is still only "a bit."

the link to the schematic you posted is meant to connect to a "charger" which is not shown

The pictures show the built charger cut-off devices, which is what that thread is about. One or two of the pictures do show the charger/s.

In our application, the bike has the charging system. The issue has been the need to incorporate a charge cut-off device - which is what this thread is about in particular.

What provides the constant current for charging? The most important thing is that the amperage is ok for the A123. afaik, the typical bike charging current is.

[DAVID THOMPSON]

on the pot install it set cut off voltage and then read it with an ohm meter out of circuit
and replace with a fixed resistor and do check the cut off voltage as it may change as components age

i am interested in it as i have a 70 watt 2 meter ham radio on the bike
and i have never had a bike that had a big enough battery
even when i did not install the radios
dave
complants on bikes
1 battery never big enough capacity (cranking amps)
2 all of them too tall in the saddle and i am 5f 11 in how do the short guys ride them
yes cruisers are short and i hate the seating position on them
3 gas tank big enough to go 200miles

[cat]

Battery capacity / CCA typically marginal. And more critical with EFI bikes, they can get weird when battery a bit low.

I think I noticed - looking at the specs of the A123 - that the Ah of a 4-pack would be pretty high, compared to what we're used to.

My R100GS "project bike" has a big battery - I think it's 12Ah. It weights about something like 4 bricks. I use it to run little air compressor to inflate tyres.

I'm about 5'8, which is marginal. Less than that, offroad bikes height is a problem.

[billr]

Battery capacity / CCA typically marginal. And more critical with EFI bikes, they can get weird when battery a bit low.

Tell me about it. My CX500 Turbo wouldn't even think about starting if the battery was low.
I can't remember the exact voltage, but the dealer told me the CPU wouldn't boot when the batt was just a little low..

I think I noticed - looking at the specs of the A123 - that the Ah of a 4-pack would be pretty high, compared to what we're used to.

Not in this instance. The basic cell is 2.3aH, so a 4 series pack to make 14 volts would still be 2.3aH.
You can parallel in as many sets as you want, 4s2p, 4s4p, etc to increase the amp hours.
4p pack would be 9.2aH. And it would weigh 2.7kg.
On the other hand, a 4s1p pack will take 100amps or better draw without damage. It'll start the bike, just need charging before you do it too many times.
Bill

[cat]

oops

Thanks.
I must find the thread on advrider where it's used on a KTM 950, and find the website of the guys selling them [as readymade subsitutes for bike batteries], see what they've used.