Project LVC for NiMH packs... Need all your help.

[BT_EMT]

Hey Cooleo help me out on this project. You talk about the "voltage drop" and I agree. (too bad I didn't know about this with my first NiMH packs, I ran them till the truck stopped rolling. The packs are "dull" at best.)

You hear all this hype about LVC devices, or ESC's with LVC like the Novak Rooster and the Mamba. So The Traxxas Stampede Forum needs to develop the proper numbers to apply a LVC device while using NiMH packs, and not go past the voltage drop. This would be perfect for newbies. The device would stop the truck, rather than hoping they figure out when to stop running it. The question is, what low voltage cutoff would be proper for NiMH packs. Trying to get the most out of a run, but not dip too low. The Mamba would be perfect cause you have fully adjustable LVC.

So what do you battery experts think would be the "voltage drop" number that would be ideal for that expensive new pack? I doubt the NiMH companies will come out with this, because they want you to ruin your pack and buy new ones !

So you Stampede owners with a voltmeter, maybe you can wait till you see the truck slowing down, or the "voltage drop" and quickly measure the pack with your multimeter. That would be a good start. I can't help out at this time, as my voltmeter fried, and my RC stuff is "out of order" at the moment...LOL The peak charger was a great invention to protect the cells on the charge end, so it only makes sense to have something to protect them on the discharged end.

[BT_EMT]

P.S. Don't play with your expensive digital multimeter measuring AMPS on a real car battery !! Thus my disabled meter.....

[papa_wheely]

Very good point, an LVC is a great idea!

[BT_EMT]

Well the discharge trays cut off at 5.4 volts. That of course would be the absolute minimum number to start with....

[cooleocool]

It would vary too much I would guess... It would have to be adjustable.

[BT_EMT]

Adjustable would be the best yes indeed, so you Mamba folks, if you would like to participate, you have the best set up for picking the right number since you can play with the LVC on your PC. That's assuming you have a 6 or 7 cell NiMH and haven't gone to LiPo exclusively.

[cooleocool]

It really wouldn't be that hard to do... It's easier to just keep an eye on it .

[BT_EMT]

Well Cooleo this is a "project" concept for me. I think it could be easily done with input from the peeps in here. Don't you think it would be great for a newbie that just got an expensive IB4200 pack and doesn't know when to stop the run ?? Part of what got me thinking about this is your story about your GP3700 pack I think it was. You said you let it get too low, and it hasn't performed the same ever since. If you had this project device, maybe it wouldn't have killed a little bit of your performance on that pack.

[cooleocool]

The thing is that the people would have to know about the cut off to buy it. If they know about it, it would be easier just to say, "don't run past the drop."

It is a good thought though! I actually wrecked three GP3700's. I over discharged them all when they were new. The punch is still there, but the Mah isn't. I've heard of people over heating their GP3700's and they've lost Mah, just as I have. Need a voltage/heat cut off...

[BT_EMT]

Well I've been thinking about the heat cut off too. Venom has that heat sensor failsafe, intended for Nitro, but maybe you can set it for about 130* cutoff. It monitors your nitro receiver pack voltage, I wonder if you could get it to work right for a full 7.2 pack.

http://www2.towerhobbies.com/cgi-bin...&I=LXJTW3&P=ML

http://www.venom-racing.com/products.../vst/index.htm

http://www.venom-racing.com/pdfs/ins...structions.pdf

[cooleocool]

That would probably work. I've been told that failsafes will work with electric vehicles. Set them to neutral...

[FP Racing]

I can't remember the battery manufacturer, but I do remebmer reading somewhere about not letting a cell drop below 1.0 volts during normal usage.

Yes, manufacturers do care about someone destroying their new pack. That's why packs or cells usually come with a warning not to fully discharge the pack. Even if a newbie does the damage on their own, it still makes the battery company look bad.

And, as it looks like you figured out the hard way, when you measure current with your volt meter: The positive and negative leads are shorted together. You don't measure the current "accross" a battery or circut, you measure it "in line". Most car batteries can put out nearly 1,000 amps when short circuited, and most volt meters can only handle 10 amps max. Although lucky for you, most volt meters are fuse protected, and you can probablly fix your meter by simply replacing the blown fuse (usually around the area where the battery goes).

Edit: Forgot about the Venom onboard heat sensor....By all reports, onboard heat sensors are very inaccurate, and most consider them near worthless. Then when you consider NiMH packs are much more sensitive to overheating than Nitro engines, I don't think an onboard sensor would be a good idea.


Fred

[BT_EMT]

Fred I think I did replace the fuse, but it still doesn't work right. I'm a "just try it" type, and I found out the hard way NOT to try that !! Good thing I dropped out of Air Conditioning school, as I just wasn't understanding electricity very well. I moved on to Emergency Medical Technician, now I only deal with a heart monitor, slap the pads or paddles on and charge to 360 joules !

[skyway0018746]

couldnt we just use a lipo cut off thing since the "power" is all the same yeah the battery config. is difftent but its still all dc power
does any one know the cut off voltage for a 2 cell cut off?

[Jakey]

I can't remember the battery manufacturer, but I do remebmer reading somewhere about not letting a cell drop below 1.0 volts during normal usage.
Yes, manufacturers do care about someone destroying their new pack. That's why packs or cells usually come with a warning not to fully discharge the pack. Even if a newbie does the damage on their own, it still makes the battery company look bad.
Fred

For many years I've been suggesting to the RC community the problems associated with over discharging a battery pack. In a RC battery pack the cells are usually connected in series; this makes it very likely one or more cells will be damaged as the pack nears an empty state. Some types of cells are more tolerant of low voltage conditions than others, but damage will still occur.
If you were to view a discharge curve recorded from the newer type Nimh cells or packs you'd see that 90% or more of the usable discharge energy occurs above 1.1 volts per cell. As an assembled pack a 1.0 volt per cell cutoff is safe so we place packaging labels warning the customer not to discharge the pack below that level.
Thank you for clearing up the misconception that battery companies want customers to ruin their new packs. That statement could not be further from the truth.
Tom Himes
SPC Racing

[Savage03]

Not sure this would help you but I have this I use on my light bulb discharger for my nimh packs. Im mostly using lipos now but a few nimhs left.
http://www.onlybatterypacks.com/show...temID=10153.13

[cooleocool]

Is that adjustable at all? Doesn't look like it to me...

[Savage03]

NO, you just puch the button and it cuts the lights off at a cetain voltage. Wasnt sure if you could use the parts to make the cutoff. I have been in the hobby so long I just know when the car slows down just stop and throw in another battery.

[BT_EMT]

For many years I've been suggesting to the RC community the problems associated with over discharging a battery pack. In a RC battery pack the cells are usually connected in series; this makes it very likely one or more cells will be damaged as the pack nears an empty state. Some types of cells are more tolerant of low voltage conditions than others, but damage will still occur.
If you were to view a discharge curve recorded from the newer type Nimh cells or packs you'd see that 90% or more of the usable discharge energy occurs above 1.1 volts per cell. As an assembled pack a 1.0 volt per cell cutoff is safe so we place packaging labels warning the customer not to discharge the pack below that level.
Thank you for clearing up the misconception that battery companies want customers to ruin their new packs. That statement could not be further from the truth.
Tom Himes
SPC Racing

Very interesting. I hope you stick around, we could use a real battery expert around here! So your packs have a warning label on them? Maybe I just haven't bought a new pack in a while. My older Dynamite Dyna Fun 3000's don't have any warnings on them, and at the time I just knew that you didn't have to worry about the "memory effect" of NiCDs with these new NiMH pakcs. I was unaware that you should avoid draining them. Well several years later I know better of course, thus my topic of a LVC for NiMH's.

So 1.0 volts/cell is a good number to set a Mamba LVC then. So do you expect after a hard run you could check the voltage with a multimeter and you would find about 6.0 volts? While that seems obvious the reason I ask is sometimes the expected math doesn't work out. Like when you Peak Charge a 7.2 volt battery, you expect to find 7.2 volts, but in reality, the pack is showing well over 8 volts hot off the charger. But then is seems to creep back down over the next few hours..

[BT_EMT]

P.S. I know a pro battery matching company cares about their customer service and people not ruining their packs! I was referring to the cheapo companies. I think if Dynamite or my LHS really cared they would have warned me, or applied some sort of warning label. How is a newbie supposed to know on a sport pack? Not many newbies are going to order from a reputable matcher like your company. Again all the more reason to develop a LVC for NiMH's IMHO.....

While you are here, aside from racing performance, care to preach the virtues of paying extra for a matched pack? I believe in it since you know the cell has been zapped, cycled several times and matched. It's kind of like having someone else break in the new pack for you, or a pseudo dyno tuned battery! LOL I'm talking about "club" grade less expensive matched packs, not the uber expensive "Team" or "Race" level packs for $70-$100plus...

And do you have any numbers on how a cheap stick pack compares to a quality side by side construction, with good wire and connectors as far as total IR for the pack, total voltage etc.?? Thanks for your time, we appreciate having a real battery company employee to talk to!

[Soonerpede]

couldnt we just use a lipo cut off thing since the "power" is all the same yeah the battery config. is difftent but its still all dc power
does any one know the cut off voltage for a 2 cell cut off?

The Novak one I got cuts off at 6.25 volts.

[cooleocool]

Would the cut off on those Novak's work with Ni-Mh cells?

[FP Racing]

So 1.0 volts/cell is a good number to set a Mamba LVC then. So do you expect after a hard run you could check the voltage with a multimeter and you would find about 6.0 volts? While that seems obvious the reason I ask is sometimes the expected math doesn't work out. Like when you Peak Charge a 7.2 volt battery, you expect to find 7.2 volts, but in reality, the pack is showing well over 8 volts hot off the charger. But then is seems to creep back down over the next few hours..

The lower priced cells I bought when I got back into this hobby a few years ago, did offer a warning about not over discharging.

If you measured your packs voltage even after a full run, it would probablly still measure around 7.2 volts or a little higher. You'd have to measure the pack's voltage while under a load. Though if you take your now discharged pack, and measured its voltage while under load (say while being used by your RC car), then yes, chances are it would read close to 6.0 volts.


Fred

[FricFrac]

I posted this info in another thread - somewhere.... anyhow here it is again. Cell Shield or Lipo Shield from Dimension Engineering should do the trick. http://www.dimensionengineering.com/CellShield.htm gives the most flexibility. If you are running LiPo or LiMn cut off should be 3.2V per cell. For NiMH or NiCd I would recomend a cut off of 1.0V per cell.

You want to cut IBs off at .9V per cell. Under a heavy load I'd give a 0.1V buffer so 1.0V should be about right. You can try 1.1V but unless you have a performance pack you may find there isn't a lot of run time.

The new Novak cut off looks decent as well but its not variable.

Its easy enought to keep your cells working just fine if you turn your truck off once you start to loose power....

[rupert]

The cellshield will not adjust low enough for nickel cells and is designed to protect each lipo cell in a series pack.

[FricFrac]

The cellshield will not adjust low enough for nickel cells and is designed to protect each lipo cell in a series pack.

Well yes and no - It will work easily with side x side packs. Solder a tap on the third cell as well as Gnd (-) an Vcc (+) and attach those to your tap on the cellshield. Then set the cellshield to 3.0V which will give you 1.0V per cell.

You can do the same to a stick pack - just take the end off the stick pack and solder a tap to the end of the stick pack.

To hook everything up it would be easiest to hook the + and - to the Dean's connector (or whatever connector you use) at the ESC side and all that would be required would be to have a connector for the tap.

[Soonerpede]

Would the cut off on those Novak's work with Ni-Mh cells?

Yes it does work with Ni-Mh. The light starts to flicker and the throttle starts to cut out and finally it just dies. Works well, but I think it also has some interference with the radio. I'm still looking for a chance to test it some more to see if my interference is coming from my new radio or the cutoff. I bought them at the same time, so I'm not sure.

[Jakey]

....So 1.0 volts/cell is a good number to set a Mamba LVC then. So do you expect after a hard run you could check the voltage with a multimeter and you would find about 6.0 volts? While that seems obvious the reason I ask is sometimes the expected math doesn't work out. Like when you Peak Charge a 7.2 volt battery, you expect to find 7.2 volts, but in reality, the pack is showing well over 8 volts hot off the charger. But then is seems to creep back down over the next few hours..

For the current IB4200 cells, 1.0 volt/cell is a good cutoff voltage while under a dynamic load. When you disconnect or stop the discharge load the pack voltage should rebound to higher levels. I personally use a charger/discharge with adjustable discharge rates and cutoff voltage. After running/racing a pack, I discharge it at 20-amps down to 1.0 volts per cell, then tray it to 0.9 volts per cell. Depending upon the length of anticipated storage time I put some charge back in the pack.
It is not unusual for a pack to read a high voltage "hot" off the charger and then slowly drop over time.

How is a newbie supposed to know on a sport pack?

Very good question to which there is no easy answer.

While you are here, aside from racing performance, care to preach the virtues of paying extra for a matched pack? I believe in it since you know the cell has been zapped, cycled several times and matched. It's kind of like having someone else break in the new pack for you, or a pseudo dyno tuned battery! LOL I'm talking about "club" grade less expensive matched packs, not the uber expensive "Team" or "Race" level packs for $70-$100plus...

And do you have any numbers on how a cheap stick pack compares to a quality side by side construction, with good wire and connectors as far as total IR for the pack, total voltage etc.?? Thanks for your time, we appreciate having a real battery company employee to talk to!

I've written several posts in the past year or so addressing these issues. You can click on my sign-on name to find them. I'm not trying to hedge your questions; I just don't want to create a conflict of interest within the forum rules.

[E-Maxx Rock's]

well i have a mm 5700 in my flm pede, im using the new ellite cells (on the graph there better than ib!!)

what would be a good time to stop?? when u notice a loss in performance or what??? i have always stopped when its moving to slow to be fun lol.. with is before the packs barely is moving the truck

[BT_EMT]

Thank you Jakey, I have read between the lines and understand your last sentence ! LOL

E-Maxx, what Low Voltage Cutoff options does the Mamba have, can you set it for 6.0 volts ? What is the default setting for Mamba? The general rule of thumb is to stop running when you see the major drop in speed. With your Mamba you can come up with some great informational numbers for us regarding run time till the LVC tells you to stop. Appreciate your input as you get it...

[E-Maxx Rock's]

u know i havent gotten to doing all of the programing, but from what i know u can ajust it any way u want it so, i know 6.0 is there....

and ok thats when i would shut off my car, i will tool around with starting wendsday as thats when my drive shafts come in, but school starts on wendsday also lol so when i have time i will mess around with it until i find it stops when i want it to, i would think put it lowest to higher to find the right setting right?

[tigger2traxxas]

thers one for sale on ebay

[tigger2traxxas]

whats the best battery for a modiried stampede

[Jakey]

whats the best battery for a modiried stampede

Modified how? Modified chassis and suspension, modified motor or all? If the motor, what type and how many turns is it? What kind of running do you do?