Getting ready to order Lipo from HobbyKing... Question

[Neo2172]

I'm getting ready to order 2 of these turnigy 5000mah 6s batteries to make a 12s 44V lipo pack for the bike I just built...

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=16207

I know hobby King has free USA warehouse shipping on orders of $100 or more. Well my 2 batteries come to $99.98. So I need something to put me over $100... I would order a charger but all the ones in the USA warehouse are out of stock... any ideas for a "filler item" from the usa warehouse to put me over the $100 mark??? I only need $.02 more!!

 

[Farfle]

you might think about picking up a two cell of the same battery, just in case you get any dead ones.

 

[Philistine]

A Cellog 8 or a battery medic (either of these are good to check cell voltage) is good to have, other small item is either bullet connectors or JST/XH 6S extension leads (for down the track if you get more packs to parrallel, to make up parrallel harnesses).

 

[Neo2172]

you might think about picking up a two cell of the same battery, just in case you get any dead ones.

Is it difficult to replace an individual cell in a lipo pack if one goes bad?

 

[neptronix]

you might think about picking up a two cell of the same battery, just in case you get any dead ones.

Is it difficult to replace an individual cell in a lipo pack if one goes bad?

Depends on which one. Definitely a nerve wracking task as 1 mistake and you will have a massive fire from shorting 1 or multiple cells out.

Always have a spare battery on hand. Hobbyking ships out dud packs from time to time, it's a well known fact.

 

[Neo2172]

A Cellog 8 or a battery medic (either of these are good to check cell voltage) is good to have, other small item is either bullet connectors or JST/XH 6S extension leads (for down the track if you get more packs to parallel, to make up parrallel harnesses).

I looked up all those items on HK and they are all only stocked at the china warehouse... It seems like all the small parts are only at the china warehouse which really sucks... they won't let you mix parts from the two warehouses in the same order...

Maybe I should just put together an order from the international warehouse? What is shipping like on an order from china?
I really wanted to order from the usa warehouse because it would be faster and of course the free shipping...

 

[AussieJester]

]

Depends on which one. Definitely a nerve wracking task as 1 mistake and you will have a massive fire from shorting 1 or multiple cells out.

.

'

Come now, Dont be so dramatic that doesn't happen easily, i have swapped ~ dozen cells out of 22v packs now, occasionally
shorting them in the process, getting the two end cells off is piss easy, it gets harder if you need to swap the center cells 2-5
some of you make it sound like they are going to explode in your face soon as you touch them, far enough
we have recently had some lipo flame up for no apparent reason but come on guys, lets not be over dramatic about
LiPO ...

KiM

p.s cool vid Luke

 

[neptronix]

Yeah, but you are the crocodile dundee of lipo repairs :lol:
Short out lipos and they will vent flame. If that's not nerve wracking, i don't know what is.
Yeah, they won't explode in your hand instantly, they would take a few seconds to do that i'm sure.
Like i said, depends on where the bad cell is. The cells in the middle are much more of a pain in the ass.

I think of it as welding a gas tank full of gas. Not something you want to do unless you have to. Not something i'd recommend to anyone either. But it can be done.

 

[Hillhater]

Order another 2 packs the same ....you will want them eventually .. 5Ahr wont last long :wink:

 

[neptronix]

^---- +1

You will also cut your voltage sag in half by running 10ah.

 

[Neo2172]

^---- +1

You will also cut your voltage sag in half by running 10ah.

Would there be much of a voltage sag? I've never used Lipo before but I was under the impression that because of the 20c rate I wouldn't notice much if any voltage sag even on 5 AH... I'm curious how much voltage sag I could expect on 5AH of 20C lipo?

 

[Neo2172]

Order another 2 packs the same ....you will want them eventually .. 5Ahr wont last long :wink:

How many miles might I get out of 5AH? I am running A stock Ebay 48v rear hub kit, riding a perfectly flat paved bicycle path, and I weight 175... think I could possibly squeeze 10 miles out of 5AH?

 

[Philistine]

I think what people are referring to is that with a 5Ah battery, you are going to be 50% depth of discharge after 2.5ah, which is a pretty short ride. Lipo holds comparitively very stiff voltage (eg compared to lifepo4), but with Lipo as you near full depth of discharge you will see voltage drop, and cells will also get out of balance, and as the pack ages you are going to run closer and closer to the voltage cliff if you run most of that depth of discharge. I have nevery run less than a 10ah lipo pack, and I consider that pack (my 10ah), my lightweight pack. After a 10km commute (about 60% depth of discharge) that pack is starting to drop volts and I wouldn't want to push it much further (I then charge at work). I personally think a 5ah pack is pointless, you should be aiming for 50%-70% depth of discharge on your pack (50% being ideal), and if you are running 2.5ah before having to charge, you aren't getting to go very far.

To answer your question about sag, it would depend on your depth of discharge, at the very begining (if you have efficient wiring etc..) you will see almost no, or maybe 1 or 2 volts of sag (depending on amp draw obviously), but as you go deeper into the discharge, you will see several volts, and then as you go right to the end, if you push it too deep you will potentially go off the voltage cliff (when you see a curve, there is a point where the voltage just dives).

The more amphours you can afford both in terms of cost and weight, the longer the life of your pack, the more continuous amps you can draw, and the less stressed you will be about pushing your pack too deep.

In answer to your question about distance, I weigh 90ish kg, and I use about 5-6ah on a 10km commute (6.2miles) (I refuse to pedal though - other than ghost pedalling) that is with a 9c or a x5, with a BMC geared hub, I would use about 4.2ah, I am happy to do that with a 10ah pack, because that is 50-60% depth of discharge. The furthest that I would be happy getting on a 5ah pack on my usage figures, would be say the BMC using just on 4ah at 10km (6.2m), as that would be 80% depth of discharge. In my view you are definately going to need 10ah to do 10 miles, unless you are going to pedal a fair bit.

 

[Ypedal]

About LiPo Repairs :

http://www.ypedal.com/Lipo/repair.htm

For an idea of what it's all about ! :wink:

I run 5ah on my commuter bike, but at 100v, so that's 500wh .. round trip is 12 kms and i use 2 to 3 ah depending on the winds ( and i don't pedal while going 55 km/h )

 

[Neo2172]

Thank you Philistine, great information! And thanks for the link Ypedal, great tutorial for repairing Lipo!

While I have made up my mind on which batteries to get (5000mah 6s 20c Turnigy bricks - seem to be the best bang for buck, correct me if I'm wrong), I still Have No Idea what charger to get... I would like to order one with my batteries from HK but every charger is out of stock at the usa warehouse. What would be a good sub $50 charger to get? Either on HK or from another source. I know the least expensive ones can only charge at 50 watts, It would be nice to get one that could charge at 200 watts though so I don't have to wait forever for the batts to charge up. So if you were me what would you buy?? (a link to the charger would be awesome!) Maybe something from hobbypartz? I heard they have free shipping, I wonder if that's true.... Also maybe I could find a better deal on ebay... would be nice if it was a usa source though, no fun waiting on the china slow boat orders...

 

[Philistine]

Those are great surgery videos Ypedal, I hadn't seen those before, really helpful.

Ypedal, I can't believe how much more efficiency you are getting than me. Maybe my CA isn't calibrated to my shunt properly, although those numbers are what I generally get both on my 24 Fet controller and my 12 Fet controller, with both CA's calibrated to their respective shunts. I generally get slightly better than a ratio of 50% of AH to km, so for 10km, I will generally use 4-5ah, depending on the motor, hills and whether I WOT the whole time (which I pretty much always do). What is strange though is that my ah usage generally lines up with my charge ahs. Maybe I haven't calibrated my scales correctly....

 

[JohnC]

.

 

[Ypedal]

I am using a crystalyte 409, meant to be in a 26" wheel and 36~48v, but i laced it into a 20" witch would make it slow as snails at that votlage.. so to compensate i cranked it up to 100v ( using 4 x 6S packs ) and 40 amps giving me 4000w on tap at launch.. At full throttle i cruise along at 50~55 km/h depending on state of charge and between 900 to 1200w depending on winds and hills but rarely over 1500w even on the windiest days... makes for a very efficient setup. ( I weigh 180 lbs on a full suspension bike that itself weighs aprox 65 lbs with battery )

 

[Philistine]

P, How many volts are you running in series? I discovered this:

It's funny you should raise that, because I run both (on two seperate bikes) 42v (10S) and 84v(20S) both @ 40amps, and I find regardless of voltages, I use the same Ah, for the same wheel/hub, for the same trip. I was scratching my head about that first, but I presume that is just because both setups share the same battery amp setting? So that you could deliver the same wattage from the higher volt setup with less amps, but if you are always using your maximum amps, and those maximums are set the same, then you will always use the same amount of amps over a period of time?

 

[Ypedal]

If you are running constantly at current limit of your controller, you are using the wrong motor !!! and wasting alot of power !

 

[Philistine]

The motor I was referring to is a 5303, and I find it pulls 40amps almost constantly regardless of what volts it is on. On my 9C 8x8 and BMC that is not the case (ie the amps change over the curve) but with the 5303 it just seems to draw 40amps almost constantly.

 

[Ypedal]

absolutely... the no load RPM of that motor on 88v is something you will never reach on the road at 40 amps, and that's why it keeps pulling 40 non-stop... lace that sucker in a 20" rim and try again !

or stick to 48v !!

 

[neptronix]

Order another 2 packs the same ....you will want them eventually .. 5Ahr wont last long :wink:

How many miles might I get out of 5AH? I am running A stock Ebay 48v rear hub kit, riding a perfectly flat paved bicycle path, and I weight 175... think I could possibly squeeze 10 miles out of 5AH?

There will be some. On 5AH of turnigy 20C, i drop about 2.5v on 10S at 40 amps.
The more AH you have, the lower the voltage drop since each cell has to work less hard.

As for range, with a lot of pedaling you may be able to get 10 miles. But that is cutting it close.

 

[Cold-E-Commuter]

Agree that 2 more packs for a 10Ah unit is best. Longer life from LiPo if discharged less than 80% not to mention the safety of knowing you will not undervolt the pack. I have 9 of the Turnigy 5S 5Ah packs from HobbyKing that I have made into a 55.5V 15Ah pack and it is awesome. Blows LiFePo4 away when on the road. The V sag is greater than LiFePo4 though and the discharge has a different curve. LiPo drops steadily until the cliff while LiFePo4 remains rather constant until the cliff. Lots of good graphs here on the Sphere for that. The math that I have done since getting the pack completed supports Neptronix that 10 miles is pushing a 5Ah pack without a lot of peddaling. Because LiPo can discharge so easily they tend to dump juice at any opportunity. My Wh/Mi has significantly increased using these, but of course so has my average speed and hills are hardly even noticable.

 

[neptronix]

The V sag is greater than LiFePo4 though and the discharge has a different curve.

Do you mean the reverse? With a higher C rate and lower internal resistance = less sag. The only lifepo4 that comes close to lipo in terms of that is A123.
Yeah, the curve is slopey for lipo, That just means you have higher energy at some times, and lower energy at others.. nominal voltage is what you have to go off of.