Mosfets? - Page 3

crazydave · #31 10-01-2003, 05:32 PM

The picture above is the moded board. nothing to see, the mosfets swap right it, and look no different than stock.

There are transitor in that area forming an H-bridge. It would seem the proportional signal is generated, and then the h-bridge switches it between forward and reverse.

The H-bridge is arranged so that it uses only NPN transistors, so I was easily able to swap them all out, but I wasn't able to get any gain in performance beyond the initial stacking of the 2 on one of the forward ones.

I believe this is because it's digital. Digital is a series of 0s and 1s, or off and ons. Hence the pulsed motor current. The yet unproven theory I'm working with now is that we need an A/D/A converter with a faster processor, to minimize that pulsing, in order to get more power to the motor. First I've got to figure out if that black box is an A/D/A converter.

I'm just kinda taking a stab in the dark, I'd like to hear your thought on this, Micro-Amps.

bdebde · #32 10-01-2003, 07:34 PM

crazydave,

Interesting theory on the da converter. Have you tried the batteries? My thoughts are that the smaller batteries put out less amps. Anyone who has done both the laymans button cell mod with 2 or 3 cells and a 2 or 3 cell with the old standard cells can tell ya that there is a big difference. A case in point, I used the batteries (stock dual) from a nakamichi racer (appear the same size as the SE bats). I put in a fet modded bit pcb and it was faster than a single cell with fets, but not so hot on torque. It certainly was not as fast as a dual cell with a stock pcb. I thought I had done a bad job with the fets or damaged something, so I took the pcb and put it in a single cell car, and presto, it was just like any other fet modded car. If you can try the old standard size cells in there, it may make a big difference. Even if this can be tried "on the bench" and use a meter to check amp output, that would answer that question. I have not tried this yet, as I only have one SE here at the moment, and am keeping it stock for now. I sent the other one to micro_Amps for his expert opinion. I actually sent 2 to him, one for me and one for him. If nothing else, he has bragging rights for the first SE down under, lol.

crazydave · #33 10-01-2003, 08:06 PM

That's a good idea about the batteries. Thing is are they 2 1.2v 70mah cells, or are they 2 2.4 35mah cells? That bench test would be a good idea, but my stupid cheapie multi-meter doesn't read past 200ma, and the batteries output more than that. You'll have to try that, and let us know what you find.

urbanavenger · #34 10-02-2003, 10:26 AM

*I have been following this forum for about a year but this is my first post. I tried the Layman's Cell mod on my ZZ SE. I went to a local battery specialist in here in Michigan and had them custom weld me a 4 button cell with 4x1.2 volt 40 mAh batteries for a total of 4.8 volts! The batteries were made by Varta and are the exact same batteries mentioned in Layman's post. I am sure of that since I also ordered the Layman cells.

I was really happy to get the custom battery when I saw it was welded and shrink wrapped and best of all It was almost the exact same size as the stock 2.4 volt battery. In fact when I fit it in my ZZSE there was no modification required.

So what happened... The proportional steering and drive both seemed to work. When I held the Zip in my hand and let the wheels spin it seemed to fly. However as soon as I set it on the floor and went I realized that the ZZ was SLOW. It seemed as if the ZZSE now had no torque. At first I thought that I just needed a charge. So I promptly went to a friends with a R/C hobby peak charger. I charged the batteries at .5 amp. When I attached a lightbulb and then a 5V LED directly to the battery the lamps lit up brightly. I definitely had good power. Yet still the ZZSE was slow (about half of the normal speed, with stuttering).

I believe this problem may be related to one of the components on the PCB operating out of spec. Over Volted. I'm guessing that the part that was faulting was the A/D/A converter itself. But that is just a guess.

Long story short I think we need to get these new ZZSEs faster. I loved the results achieved when adding 1 or 2 extra batteries to the original ZZ and I am really hoping that we can get the same or more speed out of the ZZSE.

Jtskty · #35 10-02-2003, 04:14 PM

Im thinking those button cells arent giving enough current out.

urbanavenger · #36 10-02-2003, 04:28 PM

I was thinking the same thing Jtskty... but when I attached the custom 4.8 Volt battery up to a test light it really lit brightly. When I attached the 2.4 Volt stock battery it lit also but much dimmer. I know common sense should tell us that more Volts should make more light. But it just seems that if the battery lit a lightbulb so brightly, the same battery should make the SE faster also.
Another consideration is that the stock 2.4 Volt battery is only rated at 80mAh. The custom battery is 40mAh. So if anything I was expecting half the run time. Thats why I tried to peak charge the custom battery. I would really like to understand why I experienced the stuttering and slowness. Maybe even the reciever was faulting out, Im not sure. Can anyone suggest an electronics guru that I can send the battery to for testing?

bdebde · #37 10-02-2003, 11:00 PM

Here is what I found doing a quick test on some batteries. I used a light bulb for the load.

Stock dual cells from the nakamichi racer (look same size as SE batteries) 80mah
Inrush upon connecting: just over 300 ma
steady load: 220 ma

2 150mah cells
Inrush: just over 400 ma
steady load: 270 ma

Looks like there is a difference, of course this was just a quick test. I will need to get things set up a bit better and do several of each type of battery to be conclusive.

micro_Amps · #38 10-03-2003, 04:44 AM

Guys, the general theory with nicads and NiMhs is that the larger the capacity, the larger the inrush upon connecting a discharged cell to a constant voltage charger. (delta peak charging current is different). So your results BDEBDE are correct and to be expected. The button cell pack at 40mAH is small and wont like being charged at 12C, 500mA (12 x 1 hr cap. charge) but so long as it is being charged by a good delta peaking charger there shouldnt be too many problems there. Keep in mind though, that the lower the charging current, the more power will be stored before the voltage goes delta negative (charger switches off). So if you've got the time for it set the charger at 1C and let it go, it will fill the cell almost completely. (Complete charge usually at around 1/10C) but takes ages. Keep in mind also that delta peaking can be less reliable in small cells at high charge rates. There is a higher risk the cell voltage wont delta at all and the cell will just fry.
At 4.8 volts there is a chance that the electronics in your ZZ are saturated. The car may run in your hand, whilst drawing almost no current, but as soon as you put it down and current is needed to be drawn in order to run, the controlls say 'no thanks' and you get the stuttering and lack of control. This is just a theory, but I have seen exactly the same thing on a modded new super BCG.
It sounds like your cells are ok, but the electronics doesnt like the extra voltage. I will be able to confirm this when my ZZ SE arrives (soon I hope)
Have you tried running it as a 3 cell?
I will post results along these lines when I get my car.
Cheers,

uA

crazydave · #39 10-03-2003, 09:09 AM

I was thinking with that four cell pack, maybe if you wired in parrallel 2 pairs of batteries wired in series, so that you are still putting out 2.4v, but double your mah. How fast the battery discharges also depends on the battery's internal restistance. Maybe having the the pairs wired in series will help cut the battery's restistance, because the current is being drained from 2 batteries at the same time.

Just another theory.

...but I personally, IMO, I don't believe the batteries are the problem. Figure the stock Tomy batteries are only 50mah. NiCds do have a lower internal resistance than NiMH, and the Tomy batteries seem to take more than what they're rated for, but still from that point of view 70mah for the Zip Zap battery doesn't seem that bad.

I'm gonna focus on the PCB for now, but I was thinking, we could always dual cell the SE with 150mah cells, and leave one hangin' out the back like we did with our bits, but I'm trying to avoid that, because I always prefer to keep everthing tucked away inside the car.

bdebde · #40 10-03-2003, 08:05 PM

micro_Amps,
I may have confused you with my last post, or perhaps I am confused by yours. I was not talking charge rates, I was talking dicharge rates when connecting the batteries to a light bulb for a load. While your theory holds true for charging batteries, I suspect a 50 mah tomy battery will discharge at the same rate or even more than the 150 mah ni-mh bats, for the simple fact that they are nicads (higher initial voltage). That would be a smaller capacity than the SE batteries. I may try to do some more testing on some different batteries this weekend. I think the physical size of the cell does come into play somewhat.

crazydave,
I definitely agree with keeping everything tucked inside the car!

micro_Amps,
I sure hope those SE's show up soon, it has been a week today. Then we can see what kind of micromagic you can work with these babies.

micro_Amps · #41 10-04-2003, 08:45 AM

Sorry bdebde, I did misread your post, I see now that you connected them to a light bulb. I guess I focussed on your use of "inrush" and I took it as a charging term, then I went on rambling about charging theory. I usually do my posts at about midnight, I guess my eyes (and brain) were starting to close.
You are right, the nicads will flow more current than NiMHs on the same circuit simply because they have a lower internal resistance allowing more current to be pushed out.

I am expecting the cars on Monday, I find it usually takes a week plus a weekend, then they turn up. I will keep you informed.

uA

crazydave · #42 10-04-2003, 09:07 AM

Yeah, I also hope you get those cars soon, micro_Amps. I can't wait to hear your point of view on these.

slider69 · #43 10-04-2003, 12:44 PM

I just did it....after 3 good hours with my best friend (A 15 watt soldering iron) I completely mosfetted my Enfini. (I just got it yesterday...had it for about three minutes before i mosfetted it) I put 2502s (i think there are 5 counting the 2 in the stack) on the side without the black coating, and replaced all the transistors coated with epoxy with 6401s (there are 4 on that side)....It doesn't go as fast as a regular zz tho....think there's something else holding it back...i am using a 3.8 with the blue ratio....so it should accelerate a lot faster......what do you guys think?

micro_Amps · #44 10-05-2003, 02:11 AM

If it doesnt even go as fast as a regular ZZ, then I wouldnt call it a success.
It is supposed to be an improvement, not just a change for the sake of it.
Do you know the actual purpose of the components in the circuits, why are there 5 fets?, I would have thought it would be an even number of fets.

uA

slider69 · #45 10-05-2003, 04:30 PM

They are in an H-bridge i believe..there are four places for a transistor, but two are stacked......I think it's my battery tho...the se doesnt want to charge now....I charged it up and it ran for ten seconds b4 the battery went down.....but that could be the ADA converter wasting energy or something.