LiFe Racing Packs - How to?

[DaveG28]

Ok, thinking of going to LiFe batteries from Lipo's for safety reasons really, and trying to work out what I'd need to do to keep the same speed:

1. As the voltage is lower, would I need a lower turn motor, or just a gearing change, to get a similar speed? The C x Mah would be similar to my current cells, does that mean punch is similar, and therefore if I used a higher pinion to get the speed back I'd lose punch compared to Lipo? But if I go from say 5.5 to 4.5 I'd get more punch, is it all a case of finding a balance between the 2, and if so is it feasible to get that balance right?

2. What's LiFe efficiency like? Eg all things being equal would a 3500 pack give the same runtime as a 3500 lipo? Ignoring recovering the speed! Or is it lower efficiency, like nimh?

3. Anyone with any inside goss know if some life saddle packs have been sent for homoligation this year? I only know of one such pack even being around!

[fearo]

1) I'd say a one turn motor difference would be the best option, but also take your battery C-discharge rate in consideration. I don't now what C-rate you're running know, but say you were running 35C Lipo's and you would make the switch to 60C Team Orion Life's you might not need to change a thing.

2) in my experience, Life efficiency is great, probably the same as Lipo. I have some cheap 4500 Life packs and one goes from GREAT-GREAT-GREAT-GOOD-DONE and the other goes GREAT-GREAT-GOOD-GOOD-DONE. Believe me, I used to run nimhs not long ago, and they are nothing alike.

3) I only know of one life saddle pack and it's the team Orion one. I have no idea if it will be homologated, but their stick pack is, so I think there's a very good possibility.

[MRD]

I'd guess that motor temps would be an issue when using 60c cells and trying to gear up the motor to retain the speed.

I'd work out the overall top RPM of the motors on 6.6v and 7.4, then get the equivelant motor.

6.5 LRP x11 = 6900kv = 51060 RPM @ 7.4v

51060 RPM / 6.6v = 7736kv

5.5 = 7100 kv
4.5 = 7800kv

So I'd be tempted to go for a slightly under geared 4.5 to replace a 6.5 .

Altho I could be completely wrong .

[DaveG28]

Cheers, may well work!!

Will servo's/esc's have issues with the lower voltage? I guess I need to turn off lv cutoff, but if it goes under 6v will it affect the receiver/servo's, don't they need 6v supply?

[KRob]

Most receivers will work down to about 4.8v.
It's below 4.8v the problems will occur (some of the budget rx's might be more prone than the more expensive ones).

For 12th we did not need an rx pack when using 4-cell nimh so Life at 6.6v will be fine for the radio.
Now we have 1s lipo we need an rx pack, and many actually use a small life pack...
I know the voltage is different but when losing 1v due to the nimh/1s lipo change we generally dropped one wind (5.5t to 4.5t) to keep roughly the same feel. In fact it would normally bequicker due to the better discharge band of a lipo.

I know this is working on lower voltages but I doubt the current draw would be enough to start causing issues for the receiver

[LRP]

hi if ure @ ardent tomorow i have some if u want to try 1 ??
they are 60c team orion ??

[RogerM]

Dave I have been looking into this extensively as, as I am sure I have said to you, I REALLY dislike the LiPo power delivery and am looking to smooth the car out.

The calcs I have done, not just RPM but motor wattage etc too, suggest that dropping 1 wind would give you approximately the same motor RPM but a smoother "feel" due to the way the voltage drop effects the way the motor accelerates and builds torque.

I am hoping that my planned change to Orion LiFe and Orion motors should give me back some of the 'feel' I have lost with LiPo / brushless.

As far as I know the only LiFe saddles are the Orion ones but my guess is we'll see more manufactures producing LiFe saddles in time for the all important homologation in January. Not that it matters, the Orion stuff looks to be excellent and I'd certainly recomend that you give them a go.

[DCM]

Out of curiosity, what are the general handling tips with LiFe cells?? min and max voltage, etc.

[DaveG28]

Totally agreed, sadly the deadline for submission is Wednesday though, I'm not to hopeful any will be in the list (saddles anyway) in 2011 just because so few are around! Hope so though!

Dave

Originally Posted by RogerM

Dave I have been looking into this extensively as, as I am sure I have said to you, I REALLY dislike the LiPo power delivery and am looking to smooth the car out.

The calcs I have done, not just RPM but motor wattage etc too, suggest that dropping 1 wind would give you approximately the same motor RPM but a smoother "feel" due to the way the voltage drop effects the way the motor accelerates and builds torque.

I am hoping that my planned change to Orion LiFe and Orion motors should give me back some of the 'feel' I have lost with LiPo / brushless.

As far as I know the only LiFe saddles are the Orion ones but my guess is we'll see more manufactures producing LiFe saddles in time for the all important homologation in January. Not that it matters, the Orion stuff looks to be excellent and I'd certainly recomend that you give them a go.

[burniburn]

Since a while I was looking at getting one or two of these to give it a try:

http://www.teamassociated.com/news/a...and_Shipping!/

Did anyone test these yet and can it be recommended?

[bodgit]

I,ve never looked into this but were life batteries intended for use in buggies or just as a replacement for the 5 cell tc cars. Im just thinking of what drain the wieght difference between a tc and a buggy may make.

[DCM]

No cell was intended for Car use, just some offer us the right performance. LiPo got their first with capacity and discharge rates.

[Carlos69]

There's also these from MuchMore.

[DaveG28]

Still umming and aching on these, would be looking at the Muchmore ones myself...to repeat Marks question, what are the handling tips?

Eg, charge rates, storage level??

LRP, what change in motor wind have you had to make?

[RogerM]

Dave what is wrong with the Orion cells? Are we sure the Muchmore ones have been submitted for homologation?

If you go down 1 wind (eg. 6.5 to 5.5) and put gearing somewhere between the two I think you'll be somewhere close.

[c0sie]

Originally Posted by DCM

Out of curiosity, what are the general handling tips with LiFe cells?? min and max voltage, etc.

Steve,

3.9 LiPo/LiFe batteries may be charged to a maximum of:-
2S Batteries may be charged to a maximum of 8.40v (LiPo) resp. 7.40v (LiFe).
1S Batteries may be charged to a maximum of 4.20v (LiPo) resp. 3.70v (LiFe).
Overcharging is a serious safety hazard and will not be tolerated.

From the 2010 EB regulations:
http://brca.org/?q=content/regulations/1398

Hope that helps?

[DCM]

what is the minimum voltage?

[DaveG28]

Originally Posted by DCM

what is the minimum voltage?

Technically 2v per cell, although in theory they can be dropped lower. In practice apparently about 2.4v per cell is the lowest safe voltage!

[DCM]

Thats gonna be an issue then.... will have to ask Tekin to do a voltage cut-off to suit if thats the case.

[RogerM]

2.8V/cell I believe (under the sort of load we pull)