LiPo batteries, 7.4volt Anyone?

[Joolstacho]

Is anyone using (7.4V) 2-cell lithium polymer batteries?
They're so cheap, small, and light.

6v lead acid batteries are getting harder to find, so why not use 7.4v LiPo s?
7.4 v has got to be pretty right, but what about the charging side electrongurus?

[duTch]

 Funny you should ask, I've just been going through buying some 18650's for the Metabo that blew up a while back. Nominal 3.7V each cell, but I think it'd need a fancy regulator to do it right. -Long story

[duTch]

 I posted earlier about something unrelated, can't remember what already, but we have a new member a few months ago who is clued up on battery stuff, and I was looking t see who wanted to ask stuff

Nominal 3.7V each cell,

...(10 cells: 2 banks in parallel x 5 in series)

[Joolstacho]

So, 2 cells in series gives 7.4v. You can buy them in many amperage configurations.
Example: Turnigy 5000mAh (that's a 5ah battery that fits in your pocket) 2S2P 40C Hardcase Pack, $38 ozbucks. (Thats a 2 cell in series, 2 in parallel pack).
2 of these in parallel gives a 10amp hour battery. (If you ride at night that'd be sufficient surely? if you're a daytime runner one 5ah pack will run everything we need in daytime eh? And you could put a spare pack in your pocket!)
The charge/discharge rate at 40c should give a good safety margin? C'mon electroguru's tell us why not.
(duTch your 5S2P pack is 18volt, obviously for your tool (Well, Metabo!), but we only need 6v (2S, 7.4v)

[Joolstacho]

This topic would probably be better in the 6v or 12v topic.

[duTch]

(duTch your 5S2P pack is 18volt, obviously for your tool (Well, Metabo!), but we only need 6v (2S, 7.4v)

 Yes, 18V.  I don't mean to sound like I know what I'm talking here but , do you mean Li-Ion Po, or Li-Ion...?  My understanding of Li- ion polymer is just the way it's packed in a 'bag' in a casing.

 To clarify, I'm meaning the 18650 cells (18mm x 65mm), which are Lithium-Ion. I last night reordered a pack of 20 for AU$27 to replace the ones that haven't arrived ... they are 9900 mA/h *claimed*.... these are to repack the spare Metabo 10-pack, and the one in use when it packs in, or whatever...so I may have spares to play with

 I calculate that 48 of these can be stuffed into the space that the original old 13A/h battery takes up.
  I think that's 24x9.9 A/h =~220 A/H @7.4V , but should be enough to make it home from the pub

 Apparently the Tesla cars use about 40,000 of these .

 As you say 6V batteries are getting hard to find, I bought the last 13A/h one a year ago (which died as a result of a short), and last week the last 11A/h one where I buy from, for a dry spare.
 LI-Ion cells are not a bad idea, just a matter of charging them properly I guess. I have some in a couple of portable lights, and last a while, but that's running Cree LED's.

[worntorn]

If you can somehow adequately charge the  7.4 volt batteries they might work OK.
12 volt Shorai and Ballistic batteries don't work well with Vintage 12 volt motorcycle systems. This is because these batteries actually have an operating range of 12.8 to 14.2 volts. They are fully discharged at a voltage higher than most of our systems can manage.
Shorai and Ballistic now acknowledge this problem and caution that their batteries must be installed on a vehicle with a charging system that "can produce at least 13.2 volts at idle."
I don't think any of our old 12 volt systems do this. Mine sure don't, even the two fitted with modern Alton Alternators weren't up to the job.
When the Ballistic died, it took out the entire charging system. Don't know how that happened, but others have reported the same.

I found out the hard, expensive way that Li batteries do not like repeatedly being dragged below 12.8 volts. They have a very short life when subjected to this.
I suspect that a 7.4 volt setup in a 6 volt charging system would result in similar problems, unless you could somehow modify the charging system in order to get sufficient charge at all rpms.

Glen

[mikeb]

I think worntorn has nailed it. while i'm no expert on this stuff, a lead acid 6 volt battery has a nominal voltage of 6.6v (?) and charges at 7.2v. so the reg has to pump out 7.2v to charge. Regs don't produce more volts than that or they would fry your battery. so no charge will occur if you need 7.4v to start charging. Similarly a 12v lead acid battery charges at 14.4v....

So you'd have to somehow adjust/modify your regulator for more volts. I have given up any interest in Lucas regs (eg RB108) but maybe that's possible with all those points and adjustments? However lithium batteries explode if you overcharge them (google the vids if you haven't seen them) so I wouldn't go there personally. Modern electronic regs like a DVR2 are not adjustable - maybe their manufacturer could be lobbied to make a Li version but I don't really see what problem it solves. I run cyclon batteries in the B33 (12v) and old lead acid 6V in the A10. cyclons are modern spiral lead acid gel type things. works for me

[Joolstacho]

Get all that, LiPos are less forgiving re discharging. I would have thought some electronics dude could figure out a low voltage cutout. In fact you can already get them for a few bucks. As far as charging rate goes, I would have thought that same electronics dude could utilise circuitry of one of the commonly available Lipo car chargers which have clever electronics that can charge at a higher rate than the source battery supplies. (But then what would I know, I'm challenged just keeping the smoke inside!)
Yes they can self-immolate, just need to take sensible precautions.
So any other alternatives for 6v batteries?

[mikeb]

I'm challenged just keeping the smoke inside

yeah i hate that when the magic smoke comes out. it loses its magic just like that.

what's wrong with cyclons? 2 in parallel fit inside the rubber battery boxes and makes 6v

[Joolstacho]

Aaah I was just being a cheapskate as usual, a few RC aircraft & cars in stock that I could raid for batteries for the Velo (woops, now I've said it!) 

[mikeb]

you're a cheapskate but you own an a10 and a velo??????? there are cheaper ways to live

i got my cyclons from RS on an account - actually not too bad $$$-wise compared to a motobat tho still double an old leaky lead-acid

[Joolstacho]

Hah Mike, I bought my Velocette for 80 quid in 1974, and I built my A10 up from nothing, starting with a bare frame.
(So you can see, I AM a miserable miserly ol' cheapskate!) 

[Kickaha]

One of the guys on our local site sells them and has a good FAQ about them

http://www.fastbikegear.co.nz/index.php?main_page=page&id=18&chapter=1

They also do a 6v version

I have no associiation with Liam other than being a client but have found him pretty helpful in the past

[muskrat]

A mate with a HD has gone through 2 lithium batteries in 6 months (@ $180 each). Apparently they don't like vibration and are touchy with charge voltage. He's gone back to AGM battery with no probs other than weight.
Cheers