lipo noob questions

[dogman]

Despite reading a lot of lipo threads a few things are not clear to me.

Is it ok to mix and match lipo packs of varying c rates?

For instance, say I bought some very cheap 5s 15c 5 ah blocks. 4 of them for 72v. Later on with more money, I get some better 5s 30 c blocks. Would there be a problem with putting a 15c block and a 30 c block in a 2p connection before series connecting them for 72v? This is assuming that the pack would never be used above 15c of course.

Would it be better to make a 72v 15c pack and a 72v 30 c pack and then paralell the two?

Would it be better to make a 36v 15c pack and a 36v 30 c pack and series the two to get 72v?

Or would it be better to run one 5 ah pack of 15c cells, disconnect, and then run the other 30c pack?


Another thing I am wondering about, would there be any problem with putting 5s blocks in series with 6s blocks? So you'd end up with a 22 s pack? I don't see why not, but ignorance is bliss.

I'm thinking 2p 5s + 2p5s+ 2p6s+2p6s. Those 8 lipo blocks could then be arranged in many ways to have 36v 5ah, 48v 5ah, 40v 20 ah, and 80v 10ah. Again, they may not all be the same c rate. And no way would I try to paralell 5s and 6s.

Seems like a good way to have many ways to use the lipo, besides just 80v at the spooky tooth. 5s and 6s both have their appeal, especially the price now of the 5s 15c packs.

[bart_dood]

Just a short answer, if you mix different C rates what will happen is near the end of the battery charge when it's almost used up, the lower C rating cells will voltage droop first, this puts them out of balance and if you're not careful you will run them under 2.8 volts or so and wreck them.
If you run the mixed cells way under their maximum C, for example if you had a pack of 10C and 30C mixed cells but you only run them at a discharge rate of 2C you would have less problems, they would probably get a little out of balance at the end but not terribly so.

I guess the question is are you going for performance or range? if performance used matched cells, if range at lower performance you'll get away with mixing.

Incidentally I just spliced a different brand lipo cell within a pack that had a bad cell, it's C rating might be slightly different but close. I am only discharging at 2C so I don't expect any problems as the cells are rated around 25C.

Hope this helps.

[dogman]

Your reply tells me what I suspected. The max continuous c rate i'm anticipating would be about 5c I think. I'm trying to get my act together to have a decent showing at next years spooky tooth, but the wife starts giving me that look when I start talking about new batteries again already. Especially when I want to spend $600 or so for batteries I'll use only for the racing. Lots harder to justify than getting to work.

So the situation I can imagine, is ending up with a pack made of 4cells of this, 4 of that, ect. Whatever is cheap at HK. Perhaps some of them loaners for the race, with one guy sending 2 of this, and one sending 2 of that, etc. I just don't have the cash now to order up 10 5ah packs, 8 to run, and two spares in case one arrives runty. When the race nears, we may put out a call for donated lipo to run in the heats before the main, with all kinds of people sending a pretty well used block or two. If 5 ah is enough to run 8 laps, then there would be no need to paralell them.

Out of balance at the end of the race wouldn't matter( or would it), and actually some of em killed would not be totally unexpected. Try not to, but while racing, you are likely to ignore a lvc alarm.

The real concern is what happens when you stop. Enough inbalance and does one battery charge the other till it bursts into flames? Tolerable to run 25c with 30c, or 20 c with 25c. But not a good idea to run 15c paralell with 30 c?

Obviously the ideal is to run only perfectly matched cells. You can get away with this with other chemistries, like nicad paralelled with sla. But lipo is mabye going to go off if you screw up with it.

Diodes would be the fix for the problem now that I think about it more, preventing one paralell pack from charging the other?

If you are not paralelling them, then I suppose it would be ok to series connect say a 15 c with two 20c and one 30c. Then run it below 15c. ? Or if paralelled, keep the paralelled packs matched for c rates? So 2p 15c series to 2p20c etc?

[GGoodrum]

What bart_dood describes is not accurate. Whenever you parallel cells together they will equalize to the same voltage and will from that point forward act as a single cell. The "C"-rating will be somewhere in between the two individual cell ratings. The weak cell will pull down the rating of the strong cell, or looking at it another way, the strong cell will pull up the rating of the weak cell. In either case, this is preferable than running the packs independently, only paralleled at the pack level. If you do the latter, you need to use Schottkey diodes on both packs, or the weak one could die, and pull down the stronger pack.

If you are going to run a 2p configuration anyway, keep in mind that this basically doubles the "safe" amount of current you can pull from the pack. In a single "p" configuration, a 5Ah/15C pack can deliver about 75A. In a 2p/10Ah configuration, that goes up to 150A. My point is that you can get more power available later simply by going to a 2p configuration of the cheap 15C packs. Even these inexpensive 15C packs are very strong, compared to most LiFePO4 low-end products. Hell they are stronger than any of the higher-end stuff as well.

Also, there is no issue with putting 5s, 6s or whatever, in series with each other. You should look at, however, how you plan on charging and/or balancing the packs. For charging, I'm assuming you are trying to maybe make use of your existing LiFePO4 chargers? Is that why you are trying to "fit" into the 36V/72V ranges? For LiFePO4, a 24s configuration is typically used for a "72V" setup, but the nominal pack voltage is really about 80v, and these get charged to about 88V. If your controller can handle that, it might be okay with a 24s LiPo configuration, which has a nominal voltage that is about 8V higher than the 24s LiFePO4 setup. The point I'm trying to make, is that there are cheap charging solutions now, based on using inexpensive power supplies like the Meanwell series, that let you charge at higher rates than the 2A or 5A chargers that Ping supplies. So it may not make sense to try and "fit" the LiPo configuration into an existing LiFePO4 setup.

-- Gary

[The Mighty Volt]

Noob Question:

What is the difference between ICR and IFR in LifePo4 battery specifications?

Thanks.

[chroot]

Gooddrum is right, I have 20S2p in 5s (74v nominal and full hot 83.2v), it pull lot amphere (I don't even have CA ) and it seems never goes out of balance. I abuse LiPo LOT just like Methods is doing on his LiPo.

I recommend buy 8 of LiPo in 5s1p so you can make 20S2P (74v Nominal and 10 Ah) and I would love use 6s, however I do not
want blow up my controller 100V capacitors and I don't even have backup controller.

[dogman]

Thanks for the explanations guys, It's finally coming together in my mind better now. I was thinking paralell the wrong two things and boom . So I didn't want to make an expensive mistake. Especially at the races with 20 cameras running at once. Still don't want to paralell a charged one with a discharged one!

The reason I liked the idea of so many different combinations was that I just like flexibility. I do so many different kinds of riding, on so many different motors people send me to test. I thought it might be very nice to have all the various voltages covered by having both 5s packs and 6 s packs.

Also no telling what somebody may show up with at the races," saying hey run this." I bet somebody else shows up running 20s lipo, and I also wonder if running 24s would be too much for my 72v controller. But mixing them some you could run 21s or 22s, and have a slight edge without going all the way to 24s Whoever buys that lyens racing controller is going to be faster anyway, running 30s or whatever. Unless the motor melts in lap 6. But it would be nice to have an edge on the 72v guys by having 80.

From what Gary says though, I could scarf 4 really cheap 15c packs now to get started without being screwed into buying 8 more of better stuff later, so cool. 4 of the cheap ones now, and mabye 6 more of something better later would still work.

Initially, I'm looking at a very cheap lipo charger to charge em, one at a time. If it works out good, then maybe 4 of the cheap chargers later to be able to have 4 packs cooking while I run practice laps on the other 4. One good power supply to run the chargers. I'm thinking race day you need at least enough lipo on hand to do the heat race and the main, and then practice can be run on whatever else you can come up with. So charging fast is not an issue if you have the packs for actually racing pre charged.

Practice laps and possiblly the heat race would only take 5 ah, but I think the actual spooky tooth will need 10 ah. Or rather, the race may take 6 or 7 ah, but then run enough to have a good safety margin to avoid running slow at the end of the race.

[nicobie]

Hey Dogman,

You might want to do what I did to my 48v/20ah Ping and add a 6s 2p lipo boost pack to your 48v/15ah Ping. This would give you ~83v HOC. Use a cheap hobby 6c charger to charge the lipos. Both the ping and the lipos can be charged at the same time without separating them. Be sure to parallel the lipo balance wires at cell level. You can then plug in one of the cheap cell monitors to the balance plug when not charging and have a LVC for the lipos when racing/riding. Use your CA to control max amps. With a 15ah Ping and 10ah of 15c lipos, I think I'd try running at 45a max. That would give you about 3400w total. When hooked up this way your CA will display ah used out of each battery and watts and amps for both batteries combined.

You might want to run 3p but with such a short race I'd think 2p would be enough. You could get the whole thing for about $150 - $175.

It's just a thought...

BTW I've been doing the same thing with my BMC hub motor with no problems for about a year now.

.

[chroot]

8 of 5s1p 15C cost me about 313 dollars + shipping nearly 400. Don't forget buy Gary's LVC/HVC and charger control either
assembled by Gary or buy PCB then you solder and assemble it. It's a MUST!! Why?

For your >>>> SAFETY <<<<

You wouldn't want leave charge unattended the LiPo EVER!! The 2 most important LVC/HVC combine with the Charger control
will save your butt (or your neck) very effective 4.16v per cell without letting overrun possible over 4.2v or so it will lead make fire or possible destroy your house. It also more longer cycle on LiPo at 4.125~4.16v.

Here Gary's LVC/HVC adapter and charger control:

http://www.tppacks.com/products.asp?cat=26

Like Gary said: "based on using inexpensive power supplies like the Meanwell series"
For the charger, one charger Meanwell s-350-24 sells varies from 25 dollars to 49 dollars on ebay. They will do very well
charge CC/CV mode few parallel and it also have 10% adjustable voltage. So you adjust set to 20.8v, if you bought a 8 of LiPo pack in 5s1p (4.16v x 5 = 20.8v), or in 6s1p (4.16v x 6 = 24.96v) and you can charge them in parallel. Again, S-350-24 can adjust 10% voltage (20 ~ 26.4V).

http://docs.google.com/viewer?a=v&q=cache:HsXiFePm0TMJ:www.meanwell.com/search/s-350/s-350-spec.pdf+meanwell+s-350-24&hl=en&gl=us&pid=bl&srcid=ADGEESgM-_pNattWLAfM6NJFpT5W9CY6fTI7LLrnX6ekXc0M-wkZmR9KkZEyUawzAvMU7HFOD4DRIi9aT9oZmBdvBRd4w5p1RCtfAleRRUEei_qQMmWXv3oxxIDuvl4KhkvRjVSx9PJA&sig=AHIEtbR04fBuaRJ4EeXyhSchSRdfgEIFEg

That's my 2 cents

[dogman]

I agree, that seems to be the way to go. Especially if you were to use the thing daily. I'm intending to use the lipo primarily for racing and practice for racing so It would be tolerable to take days to get the whole pack charged at first at least. I don't have to have convenience. I won't be charging in the garage. More like out in the metal doghouse 20 feet from the house. I do plan on 4 lv alarms. Not the best setup, but I think it will do for a starter.

Meanwhile while I dithered, the deal on the zippy 15c lipo is selling out, 3 left now. No money today anyway. So maybe later just buy the 30 c packs if in stock.
$319 for 4 5s 5000 mah and an imax b6 ac, plus shipping. Not so bad as a starter, and the 30 c cells can hack my lyens 45amp controller in 5 ah easily.

That would get me to where I could go back to the track and see how many laps a 5ah pack takes me, or simulate the track here by marking the distance between each corner on a straight road, and then dropping to 25 mph for each corner. Also test if the motor can take it, how big to make the holes in the cover, etc.

Using the ping won't work with the new controller, the racing is extremely harsh on the battery. I think I damaged mine just racing on the 20 amp controller. I was getting severe voltage sag by the last lap, and had only used less than 5 ah of it. So I was spiking the hell out of the amps on each corner, just hammering the poor thing.

One reason I went to the race with a "typical commuter" was to see how bad it would be damaged if at all. Future death racers better bring a bigger ping than a 15 ah. That's why I'm suddenly ready to leap into lipo.

I also wondered if I had the stones to corner that track, even at 48v. I do, still crazy when cornering a bike even at my age.

[nicobie]

The lipos will take up some of the slack amps off of Ping batteries. I thought you were getting a 72v controller?

hey... U are racing aren't you?


Shit... just do it for the fun. Better than spending $600

[dogman]

Well, last time I was riding around on the track, next time I'll be racing, mabye for tenth, but not for 30th like this year! I really hope to earn a spot on the front of the line up next time

Mabye I'm confused on exactly what you were proposing, I could use the ping for some of the power if I paralelled it with something, and then added 24 more volts of lipo. But then it's a heavy clumsy pig to throw into a corner. I will very likely do something like that for practice laps, and use half throttle to keep from killing the ping. I'm not kidding, that track is not normal riding, and will thrash anything less than 5c cells.

I want to race the main in next years spooky tooth with at least 10ah of 72v lipo, using the lyens 72v sensorless controller that kind ES members bought for me. 15 pounds of battery weight I don't even notice on the back of the bike with the motor up front.

Last years winner claims to be hitting 45 mph on the straights, so he'll still beat me, but 72v 45 amps should get me into 40 mph on a 2807. But if it can take it, the aotema would perhaps be able to hit 45. I think the win is going to take 100v or thereabouts. But to do that front hub, would take lots of money for custom forks and perhaps a 5303. Even what I'm planning may be way too much for suspension forks. Only testing will tell all.

[chroot]

9c motor hub 2807 will get you into 40-45 mph, LiPo battery is so super light weight than Ping battery. It also hardly
sag in LiPo. If you are gonna run 20s1p 5Ah in race. I wouldn't recommend 5Ah on race track and better at least
10 Ah. They are pretty very light weight. Have you see Gary's 20s3p on his folding bike.

53xx series crystalayle motor hub is too heavy than 9c motor hub. Someone can answer how heavy 53xx motor hub.

How many lap on race track? You need test doing full WOT and find how much it will burn Ah in complete lap track.

[dogman]

My 5304 in 24" rim including tire and slime weighs about 25 pounds.

Last year the heats were 8 laps and the main was 12.(in the spooky tooth death race) .8 miles per lap. 6 corners that slow you down to 25-30 mph, so approx every tenth of a mile you are off and back on WOT. Really hard on the battery. Way worse than cruising WOT at 12 amps. I was pulling close to 20 amps continuous and a 15 ah ping definitely did not like it. So it's going to take lipo to really be competitive, though headways would do if you have enough of them. Aerodynamics matters in this race, so I want lots of power in a tiny space, not big chunks of battery taped all over the bike.

The ideal thing would be to use 72-100 v lipo, and hopefully 10 ah will be enough. Even better if 5 ah would take you 8 laps, 10 including lineup and the lap after the race. Next time they race I'll be there, hopefully with the lipo to see how far I can go on a 5 ah pack. Last year they did some racing at halloween.

Really fast recharging would be good to have, but there were no plugs in the pits at last years race. If you bring a long cord you might be able to get some from the shop, but really, just bringing enough battery to run all day is the best solution. That stuff can be solved later, right now I want to get started so I can at least let people know what the power use of fast laps on that track is.

[justadad1957]

imo batteries should always be configured first to the AH needed capacity for correct cell balancing then series for the desired volts i do not think it is a good idea to pair packs for increased AH capacity
i was wanting to config a pack split on either side of bike and was thinking about possible problems with slightly mis matched packs

[dogman]

Unfortunately the RC market has no demand for 10 ah packs. Apparently the biggest ones are 5.8 ah. So you'd have to dissasemble two typical 5s 5ah pack to make a properly paralelled 10 ah pack. I suppose you could get 1p packs and paralell those, then do the series connections. Lots of wires to connect that way.

[chroot]

SOMEDAY!! RC market might sell 10 Ah LiPo, Just like they did it in past 1k Ah, then 1300 Ah, 1400 Ah then reached 5800 Ah nowtoday. I am believe that they will able reach 10 Ah in couple years ahead. Who knows!!!

You can see our ES member cell_man sells 15 and 20 Ah look like LiPo but it uses LiFeP04. That design almost same like
LiPo style.

[justadad1957]

darn i remember how hard it was to make run time in 1/12th scale rc racing 8 mins with sub c nicds 1200ma then 1400 and wow those 1700 sanyos where sweet
we used to rate cells with a 10 amp discharge to .9 v very few made the rated ma at 10 amp
and we would assemble the very best cells into our mains pack
then panisonic came out with some 2200's that would easily supply the rated ma at 10 so we started testing them at 20 amp
the rc car world is so fast now compared to back in the day

GEDC0096_1.JPG

gotta love tested and matched packs

(204.61 KiB) Not downloaded yet

30-40c * 4.5AH 135-180 amp good thing they use nice 10 ga wire
it does look kinda silly seeing the 10ga wires going to my control with what maybe 16 ga and crappy terminals
started out leaving all factory wiring intact and it is working fine but i know better conections mean better bottom end

so all this in mind and needed Ah for the death race i may have enough 18650 cells soon to make 2 16s9p packs that could be conected in series for ? 96 v system 3.3 * 32 105.6v nom
these cells are untested and may not developed my desired c rate
with a 3.6 to 3.7 per cell balance charge maybe hoc 118.4
totally nuked charged at 4.2 134.4 max volts hoc hopefully before they blow up maybe not a good idea as pack will most likely only last a limited number of these cycles but hey thats racing
because i will have a limited number of cells this might be the max volts i could make with enuf Ah for death race use also
as i could see my son and i each being able to use a 48v packs for some time if we dont damage them to much lol
oh ya this is an inexpensive form of transportation
i thought i was going to save money getting into an electric bike and for the few days i have been electricfied
all i can say is im hooked

my bike is legal on the street right now and its great for what it is

the bike we want to build is not and i fully understand that being said i will want it to be as safe as possible for my son and myself to "test ride" so with this in mind what speed controls / motors are you thinking about that could handle that kinda voltage !!!

or maybe 72v is enuf for now?

[kevo]

Gary / aka GGoodrum,
Could you post a description/jpeg of how to parallel Lipos using the balancing connectors? Also, I'm unclear how to hookup Schottky diodes for the same.
Thanks,
Kevo

[amberwolf]

This:
http://www.tppacks.com/proddetail.asp?p ... DLVC%2DHVC
if you need LVC/etc.

There used to be just a paralleling board available there but all that stuff seems to have gone away from both TPPacks and RechargeableLithiumPower.

This might parallel some:
http://www.hobbyking.com/hobbyking/stor ... arger_plug

But all of these are only to parallel for balancing; might not take the higher currents that could happen during high-rate discharge under the wrong conditions.

[justadad1957]

i dont think it its a easy thing to do way to many wires
batteries should be constructed that cells are unified into the pack as a whole battery unit
i am a newbe here but i think this is an important consideration for pack life
just think what might happen if you ganged a 10 Ah pack and a 5 AH pack that had even a slightly higher voltage
the higher voltage pack would discharge at a higher rate and could easily be damaged
as it would lose its capacity sooner
and then be like a flat tire dragging the total avg voltage down

darn i want my batteries to last for years

[dogman]

In general thats very true about too many wires and connectors. Every connector is a potential resistor. That's why the gold plated bullets.

But I don't think a 72v 10 ah lipo pack is going to be that complicated. Paralell connecting packs in pairs, then series connecting the 4 pairs of 5s lipo.

[chroot]

You can just use parallel cable from progressive RC online. Save your time. That's what im using it for my
15s2p set up.

http://www.progressiverc.com/index.php?option=com_virtuemart&amp;page=shop.browse&amp;category_id=5&amp;Itemid=1

[Russell]

In general thats very true about too many wires and connectors. Every connector is a potential resistor. That's why the gold plated bullets.

But I don't think a 72v 10 ah lipo pack is going to be that complicated. Paralell connecting packs in pairs, then series connecting the 4 pairs of 5s lipo.

Look at this guy's LiPo set-up

viewtopic.php?f=14&t=10817&start=1035#p256133

-R

[dogman]

Drools on the keyboard...

Assuming those are 5s 5 ah blocks, that's impressive. 21 packs there. I'm contemplating an 8 packs x 5s 5 ah setup. For shorter runs, maybe even just run 4 at a time like for practice laps. Making plans for a stout container for them so they are crashworthy.