LiPo for Bike lights?

[Jamesdh266]

Why dont manufactures use LiPo Batteries for bike lights? They are lighter and can be made into any shape. I know they have a soft shell and need a hard case added but that doesn add much weight and most LiIon packs have hard cases anyway? The RC crowd uses them almost exclusively now.

Does anyone use them for their DIY lights? If not why not?

 

[dhiris]

I've evaluated them for my DIY light and they are expensive and heavy. To compare, 4 LiIon cells in series give you 14.8 volt up to 3 Ah for 30$. A LiPo battery pack with the same specs costs ~120$ and is heavy.

 

[Jamesdh266]

LiPos have a higher energy density and cycle life than liLons and price wise they are not that much more expensive, if anything they now compete on price levels.

Zippy are a good make of LiPos and they sell a 3A 14.8V for $32
http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=8852

They might be more fragile with charge discharge but if you use a goot protection circuit and charger I dont see why it would be a problem.

 

[marcopolo]

I ONLY use LiPO for my lights now. I use the cheap e-bay ones - they are excellent with a few minor points: They are rubbish for RC as they load down too much under RC loads, but for bike lights they are superb.

One of the li-po's i'm using is a Winforce 4000maH 18.5v 5s lipo at 420g. This is comparable energy/KG to the best Thunder Power Li-po's. They were only £20 each including shipping. Up to 4A load (1C load) they are good. BUT this is why they are so cheap - load them up to 2C,3C and the votage starts dropping badly. This is not desirable under RC loads for which the batteries are generally intended. But for bike lights, we don't see this problem as the load is far less. A Thunder power Li-Po will just keep the juice coming right up to 20C rating - thats about 80A!! The e-bay ones I use would puff and explode at these loads!

Another point - take care about battery placement. If you spill big time and puncture the battery you better make sure you're not still clipped into the bike! The insides of your legs might get a little crisp & black.

Marco

 

[unterhausen]

they aren't as heavy as liIon. I think the problems with charging them, the costs associated with putting them in a case safely and the cost of the cells probably are reasons enough to explain why they aren't used as much. I do use them, although I need to get a driver with undervoltage protection.

 

[LukeA]

I do use them, although I need to get a driver with undervoltage protection.

I built a low voltage cutoff that goes inline right after the battery. It's pretty simple. I'll publish it here pending a little testing.

Right now I'm waiting on a new battery--I designed and built a Li-poly light, designed the LVC, then fairly promptly killed the unprotected battery when the light got turned on in my car's trunk. Then I put together the LVC.

 

[unterhausen]

I ran three packs to undervoltage condition, but they seem to have recovered ok. You'd think that it would be easy to tell the cells were low on the road, but that wasn't true for me at all. I'm going to use the light again, this time I'll get a big enough pack to ride all night.

I'd like to see your circuit.

 

[brad72]

It's my first post on CPF so hi to all.

I'm glad to hear that other use lipo's for their lights. I have plenty of 3s and 6s lipo's from my rc helicopter days. Coupled with a good balance charger I dont think you can go wrong. Still toying with 3 mc-e light driven from the 22.2c 2200mah 6s lipo. But, do i really need that much light

Having a cell punctured in a fall is a concern however but you could always buy a hard cased rc car battery. There pretty cheap on fleabay but not as cheap as soft lipo's

How did you all go with the battery protection. I was just going to install one of the battery indicators with buzzer that connects to the balance plug. If it starts beeping, just stop and change the battery

But the question still remains, which is the better choice lipo or li-ion

 

[Jamesdh266]

@ LukeA: I would be inteterested to see your protection. I am struggling to find a PCB that will do the job. I need one that doesnt have a max current draw or one above 6A (dual P7).

I have some good LiPos for my PC heli and am only going to try the cheap ones for the lights where I agree they should definately be sufficient. Using one of those low voltage beepers is a really good idea. I have one on my heli but didnt think about using it for my lights.

I was thinking of wrapping the battery in a thin ally sheet. Maybe 0.5mm thick, wont add much weight but will be enough to prevent puncture. Will it explode if punctured though? I thought it would just leak?

 

[brad72]

Have a look at this link. It shows what could happen when a lipo is punctured. certainly enough to keep you warm on a cold winters night

http://www.youtube.com/watch?v=4OsBc8RqSKU

If you don't get a fire, you will certainly get a lot of smoke and heat.

What happens though if a li-ion battery gets damaged?

 

[LEDAdd1ct]

I think those videos are a pretty good reason I would not want them near my legs...if I were to build a bike light battery pack, I would probably go with iron phosphate.

 

[LukeA]

@ LukeA: I would be inteterested to see your protection. I am struggling to find a PCB that will do the job. I need one that doesnt have a max current draw or one above 6A (dual P7).

It uses a TO-220 size MOSFET so the max current is in the 50A neighborhood.

 

[pe2er]

Have a look at this link. It shows what could happen when a lipo is punctured. certainly enough to keep you warm on a cold winters night

http://www.youtube.com/watch?v=4OsBc8RqSKU

Alright, That settles it. No LiPo for me ;-)

 

[marcopolo]

Where I ride there are no gangs of nail in stick wielding munchkins that are accurate enough to hit your li-po pack when you pass them at 15mph.

We tried this with some nails'n'sticks and the best we managed was a hissing sound with some smoke! They were li-pos with a few puffed cells.

If you like I can direct you to 100's of horrible things that can happen when you are cooking. Doesn't stop me eating.

Point is poeple - get things in perspective. The chances of the vent with flame even after many major bike spills are extremely low. Especially when the pack is wedged somewhere in your diamond frame or behind the saddle. Backpack li-po - maybe not if your weight came down on it.

Cahrge with dedicated charger, in LI-PO safety sack, don't leave in car or charging unattended. Store in metal box. My pet goldfish could follow these instructions. Google Li_PO care. You got to be nuts to ignore the benefits.

Keepin' it real!

Marco.

 

[brad72]

Have to agree with you marcopolo. Lipo's are as safe as the person using them. Even with some pretty heavy RC helicopter crashes nose fist into the ground, bending the lipo like a dogs leg, nothing spectacular happened, except explaining to my wife why I need to buy another battery pack.

I personally love the lipo,s. With a good balance charger you know exactly what the condition of each cell is and really you can't go wrong. You woundn't just strap a bare pack to your bike without some form of cover but that is just common sense.

The video was more for dramatic effect to visualise what can happen if your careless.

Remeber, li-ion batteries can also explode if they are handled incorrectly as seen here:
http://www.youtube.com/watch?v=f30fBFitkSM&feature=related

But as marcopolo said, how many trails do we ride on that have nails flying at our 100x40x25mm battery packs. We should really be banning nails... lol

 

[unterhausen]

I was flying my model airplane one evening, and something flew off, then the plane stopped responding. It was the lipo, which flew 50-100 feet before hitting the ground. It still works. As long as you don't have it set up so something will puncture in a fall, it will be fine. I hang mine under the stem, possible but unlikely to get punctured.

Most batteries will explode (rapid venting with flames as we like to call it) under some conditions. The ones that come in cans have a vent, but they can blow apart with some force if shorted internally.

 

[chris_m]

they aren't as heavy as liIon.

Can somebody give me a link to these lightweight ones you're using? Unless I'm missing something here, they're actually heavier than LiIon - I wondered if things had changed since I last selected batteries, but I did a quick check and they haven't. A typical 2200mAh 11.1V LiPo battery I found is 175g - that's compared to the <50g 2260mAh 3.7V LiIon cells I've been using for years.

Regarding overdischarge protection, I've always used low voltage detection and cutoff in my driver circuits - back in the day that was a PWM halogen regulator, nowadays in my custom Maxflex/bFlex firmware (though they now come as stock with low voltage cutoff). Don't see any need for external protection if you've got this available.

 

[Jamesdh266]

A 11.1V lipo will be heavier than a 3.7V LiIon.
But a 2.2Ah, 11.1V Li-Ion weighs about 185g

http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=4895

comapred to a 2.2Ah 11.1V Lipo 168g

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=6518

What are the cutoff voltages on the maxflex and bflex?

 

[brad72]

Chris, I hadn't even thought about usng the drivers with low voltage cutoff. Great idea.

I am going to install one of the cheap digital battery monitors that connects to the balance plug. The monitor cycles through each of the cells and indicated numerically the voltage of each.

 

[chris_m]

A 11.1V lipo will be heavier than a 3.7V LiIon.

Yes, about 3 times as heavy, but then the 3.7V cells I was quoting are more than 3 times lighter than the 11.1V pack!

That LiPo is a tad lighter than those I'd found, but you've got to compare like with like. The LiIon pack has a built in PCB, which the LiPo doesn't. Anyway, as I mentioned, bare 18650 cells are <50g, so it shouldn't be too hard to put 3 of them together to weigh the same as that LiPo pack including wiring (I'm struggling to work out where the extra 40g is in that LiIon one even with the PCB). I'll put one of my packs on the scales tonight to see what's what.

What are the cutoff voltages on the maxflex and bflex?

You can customise them through the menu on the stock firmware (I use DIY firmware, so don't go into that).