Li-poly batteries in a bit/pht2 or ma please look

[HACHI-RYOKU]

I managed to get a 3.7volt/145mah li-poly battery installed in a bit. As usual I can t post the pic. This pic below probably doesn t work.

Anyways, I installed PHT2 s patented dip switch to protect the cells from discharging completely while not in use.

The problem I m having is that some of the fets (single stage fets) start to smoke when I try to run it. The same thing was happening with the quad cell I made before. What the hell am I doing wrong? I had to send the quad cell to MA to get the fets wired differently. I can t send all my cars to MA, I ve got too many mods to do, and not enough money to get them all sent to MA.

The quad cell eventually killed one pcb because I kept trying to trouble shoot it. I m not going to run this car until I get some good ideas first. I don t want to burn anything out. The pcb still works. I took it off and put it on another car and it worked like a charm. Incidently, I put a SBCG pcb on the li-poly car and it wouldn t even function.

It s also very sluggish with forward or reverse. The nonfetted steering works fine.

Anybody got some techy info I could use? I figure it s gotta be something with the fets.

Edited by – HACHI-RYOKU on 17 May 2004 01:26:44

[HACHI-RYOKU]

WOO-HOO! I got it running. I found out what the problem was and figured I should let you all know, because sooner or later someone might run into the same problem. IT WAS THE FRICKIN MOTOR. YES, THE MOTOR WAS DEFECTIVE. I changed the motor and it decided to work. This thing screams bloody murder now.

Basically, a motor has a minimal current that it needs in order to work. Something in my motor was broken and made the motor require way more current. I checked it with a volts meter. It had super high resistance (ohms). So if you try to power the motor without enough current then it may make something very hot, i.e. the fets. You wont notice this in cars with less power, because the smaller battery wont do much damage. But I am using a 3.7volt-145mah-1000ma battery (it will actually put out 1.3amps for short periods, i.e. <10sec). Plenty enough to cook with. I still have some tests to run it through, but I will post more info on it as soon as I can.

If any of you remember the quad cell I was having the same problem with, then I have to say that I may have been using the same motor. Now I know why my two fastest creations were killing pcb’s. By the way, it was a perfection 3.8. This is the only one that has ever caused me any problems, and their motors usually run better than any other motor I have, so I wont loose faith in that company yet. But it’s definately got me a little causious now.

Edited by – HACHI-RYOKU on 24 May 2004 21:02:12

[ph2t]

interesting find there mate. I think you might find that that the motor was SHORTING itself out therefore leaving nothing to keep the current through the fets down. This was possibly what cause your fets to burn out, given the excess current load. Hell, it’s lucky you didn’t put biff on it! lol….

ph2t.

[HACHI-RYOKU]

Actually I did put biff on it. But I only ran it in short bursts. As soon as the fets got warm, I stopped running it. I also tried a stock bit and stock cyclona pcb on it. Same symptoms. All those pcb’s couldn’t be wired incorrectly. That’s what gave me the idea of trouble shooting the rest of the systems with a multimeter. It still gets a little warm sometimes though. Just on one wire though. A close up exam on that wire reveals a little damage to the wire. Looks like a small cut or something. Easy fix. But I’m also going to hard wire the motor to reduce any excess resistance or possibility of an open via vibration. The motor is puting out enough juice to shake itself out of its compartment (yes, the motor cover is in place and tight). This may create a partial open and represent the symptoms. Biff is running it well though. I might change biff to a single stock cell car though. I’m a little worried about running it in that monster. Still need to work out some performance issues as well. Just finished perfecting the position on the miniture ball bearings I installed. They are great. Even though there is an amazing amount of power going to the back whells, the bearings keep the back axle super stable. It helps tremendously with keeping the car straight.

[ph2t]

wow, great stuff mate, you’re gonna have to show us some pics of this monster!

[HACHI-RYOKU]

I’ll need to get betty k or someone to host my pics. Webshots is causing my computer problems and I can’t post on my gallery anymore.

I’ll PM betty-k, but I’ll be checking this later too, so if there are any volunteers to host my pics, then speak up now.

[ph2t]

email them to ph2t@tpg.com.au, I can host ’em 🙂

[HACHI-RYOKU]

Hey, ph2t. I’ve been studying up on these batts and resistance. Am I correct to assume that a motor with no resistance will be the same as shorting a battery out and expecting the fets to handle it? That being said, would it be better to run a 3.0 than a 3.8 or 4.2 (to reduce heat)? Also, I picked up a motor recently that’s bigger than a bit motor, but only by a little. It’s about double the width and 25% longer. I was thinking of throwing one of these in a bit with a li-poly cell and some fets. Good or bad idea?

Mainly, the real question is; if I hardwire the motor to reduce resistance, will this create more heat on the transistors?

[HACHI-RYOKU]

OK fellow bit heads, this is a list of tools and parts that I used.

Needed for the li-poly battery instalation:

1. kokam lithium polymer 145 mah battery cell (source:http://homefly.com/)
http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01161.JPG
2. extra wire
3. on/off switch (homefly.com)(basically, get the smallest one you can find)
4. xi li-poly battery charger (made by WES-Technik. homefly)
http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01162.JPG
5. A stable 12 volt source (I use an ac wall adaptor from radio shack, but any 12 volt wall adaptor with 100+MA will work)
http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01166.JPG
http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01163.JPG
6. Soldering iron, solder, solder paste, a damp sponge and pick-ups/tweezers
7. electrical tape
8. an extra charging station
9. dremmel or any good rotary tool.
10. a good small file.
11. super glue
12. glue gun w/ glue (you can use any kind of cement/glue you want. I’ve recently found a glue gun to be very useful, although it would be cheaper to just use many many coats of super glue

I had to cut of the contacts that the litium battery came with. I didn’t cut them off completely, I only trimmed them down to help it fit better. DON’T USE METAL SCISSORS. I shocked the piss out of myself when the scissors shorted out the terminals (DUH!). They come partially charged. I threw that battery away anyways. I had also decided to open it up and look inside. Don’t do that though. It may be hazardous material in there. Look at the link to see how I positioned the battery.
http://users.tpg.com.au/ph2t/HACHI-RYOKU/Lipoly2.JPG
I had to put it sideways and at an angle. The on/off switch is installed underneath it with super glue and glue gun. I dremmeled a small hole to access the on/off switch. I also dremelled a ton of space inside the battery compartment to accomadate the battery.
http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01158.JPG
http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01157.JPG
http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01155.JPG
http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01154.JPG
http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01153.JPG
http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01152.JPG
I folded the loose aluminum sides of the battery and wrapped it with a little electrical tape to help it fit better.

As far as running this kind of battery, well it’s not as hard as it seems. The on/off switch is a MUST. Basically these bateries cannot go below about 3 volts or the battery will not recover. But, that’s supposedly easy to notice. Appearently, from info coming from a hand full of people that use them in r/c cars and r/c airplanes, you’ll know it’s time to recharge when it drops significantly in performance, i.e. the car slows way down. With proper use though, they will last much longer than nicads or nimh, and only loose about 5% of thier total capacity within a year of constant use. I haven’t done any all out sprinting or time trials with this battery yet, so you’ll have to stand by for that info. So far I’ve only taken it on casual stroles. I’m still perfecting it and watching things like fet tempuratures.

IMPORTANT NOTE- Most bit cars have a constant draw at all times on the battery. It’s only about 7 ma, but that will eventually drain the battery. If the li-poly cells are completely drained, they will not recover. That’s why I installed an on/off switch. This way I can turn off the power supplied to the car and spare the batteries. Look for some info on ph2t’s “dip switch”. It gives complete instructions on how to install an on/off switch. Basicaly, you just need to cut one of the wires coming from the battery and solder each end to an on/off switch. The switch just uses a peice of metal inside to connect the two wires together in the “on” position and again moves that piece of metal in the “off” position so that the wires aren’t connected. I like using a glue gun to position the switch because the super glue tends to get all over the place and you may get superglue in the switch. Certain superglues will conduct electricity, so even if you don’t accidently get some inside, you may still short out the system with superglue.

For the wheel mod:
modifiers toy car. I love these cars, because they came with two set of rims and tires, as well as a handfull of extra parts like mufflers and foils and stuff that have potential to be ripped off the cars and used for body modding. It’s sad really. Somebody put a lot of time to produce a quality toy and I disect it and throw away the un-needed parts before it even gets to see the light of day. I had to use my dremmel to get the wheels to fit on and also to make a little extra room in the wheel hubs. Not to difficult but you may prefer a small file.

http://users.tpg.com.au/ph2t/HACHI-RYOKU/DSC01151.JPG
NOTE THE ON/OFF SWITCH BETWEEN THE TWO CHARGING TERMINALS.

For the ball bearings:
Honestly, I forget. I’ve had them for a while. But there are plenty of places to find them. A good hobby store usually has them. They are common in slot cars and some slightly larger rc cars. I got one with a hollow hexed shaped axle because I figured it would hold on to the wheels and gears better. Again, I used the dremmel to make room for them, but I wouldn’t actually recomend this to other people. I am extremely skilled with a dremmel, so I can get away with this method. Otherwise, it’s very difficult to cut the precise measurements needed for the ball bearings to fit with a dremmel. My recomendation is a small file and lots of patience. Get a marker and draw exact cross hairs around the current axle position. Now file the hole so that the axle will be positioned in exactly the same spot. I also went ahead and threw a 3:1 gear ratio on the axle. I also did this with a dremmel. But I also had the perfect size bit to throw on the dremmel for these holes. Again, I would recomend a file and patience. If the hole for the gear or the wheel is off by just 1/2 of a mm, then the car will wobble and spin out all over the place.

Also, the biff came from ph2t’s skilled hands.

Let me know if I missed anything or if you have any questions.

Edited by – HACHI-RYOKU on 26 May 2004 02:21:19

[HACHI-RYOKU]

The pics are up! Thank you ph2t.

Another note, homefly doesn’t accept credit cards paypal payments, but I like the service anyways. Good prices and prompt service. He’s also got some other things that I noticed may have some potential for bit racing.

I also found a source for the ball bearings.
http://www.ncphobbies.com/cgi-bin/vcat/CatalogMgr.pl?cartID=b-2753&SearchField=all&SearchFor=ball%20bearings&offset=11&displayNumber=10&template=Htx/search.htx&displayNumber=1

This site was previously noted for some good parts as well. Thank matic for the skinny on this one.

The original idea of using li-poly cells came from a dude named johnk from the micro rc resource center. He put them in a ZZ.

The ball bearings idea came from ze crazy Germans!

At least this is the first places that I noticed them.

Edited by – HACHI-RYOKU on 26 May 2004 01:51:13

[betty.k]

sure you didn’t leave anything out?!!:D nice work man, that is an awesome ride!:8ball:

[HACHI-RYOKU]

Yeah, honestly it was a pain in my arse, posting all this stuff, but I remember seeing things like this and not being able to figure it out because something was missed. Thanx duder.

[matic]

I was thinking to take two 80 mAh Li-poly cells wired in paralell instead of one 145 mAh cell. Measures of 80 mAh are 15 x 20 x 4 mm, so two of they will fit in the chassies better and capacity will be 160mAh.
Can 2 parallel li-ion cells be charged simultaneously as single with double current ?

[HACHI-RYOKU]

I would say no. But honestly, I wouldn’t know. ALTHOUGH, you can charge li-poly batts at C100, witch means the fastest current you would want to use is equal to the mah. I.E. 80mah batts would use around 80ma to charge and that would take about an hour. So, if you have two 80mah wired in parallel, that would be 160mah. You could test it to see how long it would take to charge. If it takes 2 hours at 80ma to charge, than you know you can double the current.

I would like to know how it goes. Let us know.

[micro_Amps]

Quote:

Can 2 parallel li-ion cells be charged simultaneously as single with double current ?

Yes they absolutely can. Once they are connected together in parallel they can be considered as ONE cell, and charged at 1C accordingly. So your 2 x 80mAh cells can easily be charged at 160mA for 1 hour.
:)uA

[micro_Amps]

BTW, very nice work there Hachi, as always you have taken the time to do your homework first and come out with a very good result.
:)uA

[HACHI-RYOKU]

Well thank you MA.

[matic]

Is max current for charging li-poly 1C ?

[micro_Amps]

Yes, if you go much higher the cell will heat up and if it boils inside the casing will expand like a little balloon and its not reversible.
There are rules that need to be followed for charging LiPos, and 1C maximum is one of them.
:)uA

[betty.k]

trash put this link up a while back and i find it very useful and easy to understand.

http://www.batteryuniversity.com/

covers nicad, nimh, lipo and lion batteries and their chargers:8ball:

[HACHI-RYOKU]

Hey all, I just finished some work on the car. I put in 2 npn fets and 2 pnp fets. I was going to double and triple stack them but after running it with single stack I came to some conclusions.
1. The fets no longer heat up. Now the car can run indefinitely without overheating the fets.
2. I don’t need to double or triple stack the fets. The thing won?t stay on the ground as it is. Mind you, it has the “modifiers” wheels that have almost no traction, but it will still pop wheelies on all but the slickest of surfaces. I couldn’t even imagine what it would do with sticky tires.
3. Other people need to try this! This may be the fastest mini car I’ve ever seen first-hand. This is way faster than my quad-cell. I can’t get a good speed check on it until I get a hold of my digital speed checker.

The only thing I need now is a booster/2-speed pcb. It’s insane to take off at full power. While I’m in the middle of moving (recently moved back to the states), not all my supplies are here yet. All I have available is single speed pcb’s at the moment. Hopefully, in another week or two my other boxes will start showing up. Or i might fins a 2-speed car to get the pcb from.

Just so we’re on the same page, I used 2 IRLML2502 N-channel fets and 2 IRLML6401 P-channel fets. You can not use this combination on stock single cell cars because the P-channel fets require a greater “on” voltage. Although I have to say it was a little easier to use this fet combo because all the fets fit in like the old transistors. I didn’t need to flip anything or do anything special.

Why does this seem to work better for this car? Why did the npn fets get hot to begin with (the spec sheets showed that it would take the voltage and current that I was using)?
I’m not an electronics engineer, so I may not have all the facts, but I recently read about repolarizing npn transistor gates to make them function in the place of the pnp transistors, witch is what we normally do with the famed fet mod that uses four npn fets in the place of 2 npn and 2 pnp transistors. Well, apparently, what I got from this literature, was that when you repolarize a transistor and make the current flow the “other” way, this somehow lowers the performance capabilities of the transistor. In other words Power can’t run as efficiently through a transistor when it’s going the direction it wasn’t designed to. Hence, the hot fets??

[matic]

Quote:

Yes, if you go much higher the cell will heat up and if it boils inside the casing will expand like a little balloon and its not reversible.
There are rules that need to be followed for charging LiPos, and 1C maximum is one of them.
:)uA

Thanx uA, I was actually thinking if this is maybe just a “safe” current approved by the company, like warnings on alkaline batteries which says “do not recharge” or something, hope you know what I mean…. I think I read somewhere if you charge it with 2c that it just reduce the cell lifetime, nothing else… Has anybody tested this?

[matic]

Quote:

I couldn’t even imagine what it would do with sticky tires.

Try to use AJS sponge tires AJS1000 available at http://www.ncphobbies.com/. Use them with alloy or pullback rims.
You won`t be dissapointed….

Good job, btw

[HACHI-RYOKU]

Yes, I’m going to have to invest in some of those.

[matic]

..and you will throw away all your stock wheels 🙂

[micro_Amps]

Quote:

I think I read somewhere if you charge it with 2c that it just reduce the cell lifetime, nothing else… Has anybody tested this?

Be warned, this is not merely a manufacturer warning, if you charge above 1C you will destroy the cell.
Let me put it this way, if you charged a LiPo with a standard peak charger at alot more than 1C the worst that can happen is this……
Firstly, cell heats up,
Then electrolyte inside cell boils, vapourising, and inflating the cell,
By the time the cell is fully inflated cell will be almost at ignition temperature,
As the cell ruptures the flammable electrolyte catches fire,
This ignites the insides of the lithium cell which will burn like magnesium until it runs out of fuel, it cant be extinguished.
I’m not joking, Lithiums are dangerous if handled incorrectly.
I know of one instance where a guy had his 4WD burnt out because of a LiPo cell. So be careful with them, dont leave them charging unattended.
Also, just to demonstrate how fragile their chemistry is, if you excede 4.2 volts while charging, the battery will be ruined permanently, throw it away. Thats why they need a special charger.
End of rant.
:)uA

[matic]

Amen to that. Thanx.

[jamiekulhanek]

Holy shit, they are fussy little buggers, i’m about to buy some of the 3.7v 145 mA kokam 3.5 gram ones for a 3 channel LXX plane 2 spd/rudder/elevator with biff and twin 3.8’s in a Hangar Rat……can’t wait!!!

[HACHI-RYOKU]

On to the next problem. The motors. I destroyed a 4.2 king within a matter of about 15~30 minutes with this car. The power supplied builds up more heat than I’ve ever seen. It melts some of the plastic in the motor compartment and I definitely can’t touch the motor or heat sink. It’s too damn hot.

Anybody have any ideas to reduce heat? I remember seeing something, but I can’t find it now and I don’t recall what it was.

[matic]

Maybe you can use one of the heatsinks which are used for cooling the standard transistors (silver, cylindrical-shaped ones)… I think diameter is approximately the same as motor ….
You might need to cut it (or the chassis) to fit.
I really doubt that this will prevent motor to die, since I destroyed a few motors ( 3 x 4.2 king, 2 x Phast,1 x BCG 4.0 and 1 x 4.2 Pro )
in a few months just with dual-cell-fet cars…
Maybe with watercooling…..:)

[HACHI-RYOKU]

You know, a small water cooling device may not be as hard to make as we think.:evil:

Sounds like a new research project. I may end up pretty bored after getting this thing in tip top shape. I think I have more fun modding than racing. Of-course, everything’s more fun at mach 1.

[jamiekulhanek]

dunno, sounds a bit too over the top…

[merc-blue]

theres a couple of li-polys on the ebay.com.au for thous who want some

[HACHI-RYOKU]

Well, I used a superslick motor. It’s much easier than trying to weld a mini water cooler.

It works awsome and is much faster anyways.

[Author]

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