Lipo Conversion question (probably stupid but I need to ask)

[rraeford]

I have a couple of older Associated 1/12 scale cars (raced long ago) that I use to do speed runs up and down my street. My Nimh packs have just gotten to the point of exhaustion from age and non-use. I got a couple of 1S Lipo batteries that I use in a my 4wd car (pretty new batteries). They are well-cared for and charge up fine. I decided to put one in my RC12i. The radio and esc in the car are older (Airtronics FM and a Tekin esc)—no brushless. So I take it out to the street and I notice it’s fast but it wants to spin out like crazy and even when I slowly speed up, it wants to dart about a bit which is not how it drove before. I think the lighter weight of the battery is playing a role here but I am wondering if there is some fundamental thing I am not doing to adjust for the lower voltage of a 1S battery. Maybe something so common that people don’t mention it anymore because everyone knows about it or because so few run 12th scale anymore. I’ve looked for information on a few sites but didn’t seem to find what I was looking for. I’ve been racing and driving for a long time and this seems almost like radio interference but it’s not that random. It feels like the power is just coming on suddenly and the chassis can’t handle it. I am running a hot motor in it but I should think it would be slower running on such lower voltage (7.2v vs. 3.7v). My car isn’t tweaked, my tires are new and super soft. My street is dead smooth and my other car (also a 12i with similar equipment but running a smaller 2S pack) doesn’t act this way—and it is stupid fast. Any advice? I’ve read about power boosters but nothing definitive. Maybe switching to a modern 2.4 ghz radio might help. Any thoughts out there? Thanks.

[Basher67]

Fully charged, your lipo is more like 4.2 volts and if your nimh battery was exhausted, its possible that you were dipping below that very soon after turning the car on. Nimh batteries start dropping off in voltage rapidly the moment you start running them, even when new. Lipos drop voltage much slower. It's possible that after driving your car for just a couple minutes, your wore out nimh had lower voltage than a new lipo. Also, with an old tired nimh, you may not have been getting enough amperage/discharge rate to keep up with a mod motor, where the lipo is giving you all you need.

[rraeford]

Yes, this is likely true but the Nimh pack was 6 cells and I have several packs (2 of which are less than a year old that I use for my son’s cars). Using one of those did not change the equation. I have a 12r5.2 that I am getting ready. This one will use all new electronics (though still not brushless). If I get the same behavior I will assume it’s the gear. Or, I may just buy new Nimh packs and forget tying to update the 12i since it isn’t a real problem. I was just curious if someone would chime in and say, “oh, don’t you know? You have to use a an Rx pack with a 1S or a specialty esc,” or something like that. BITD, working in a hobby shop, every other person who came in would say they were getting radio interference. Upon examining their car, we would see they didn’t have capacitors soldered to the motor can. Once this was done, no more radio interference. This was a common mistake people made but it wasn’t always written down. I was thinking my issue would be something like that. Unfortunately, in our time, there is no hobby shop expert to go ask— but that’s a subject for a different thread.

[juicedcoupe]

I think the problem that you will run into on this forum is that many people don't run 1S batteries, particularly with older electronics.

If you think that many be your problem, it is easy to find out. Pull out the positive esc wire and put a 4-AA receiver pack in. I'm sure we all have those laying around.

[matt1ptkn]

If its darty under load, I would wager that your mod motor is pulling more power than what the 1s is supplying to the ESC, and causing brown outs, or momentary power losses, to the receiver/servo. I agree with the suggestion to try a receiver pack or you could try a voltage booster, that would supply a steady 6v to the receiver/servo at all times. We run several 1s oval pan car classes at my local track, and everyone either runs a receiver pack or booster for this reason.

[Coelacanth]

When I resto-modded an RC12L3, I upgraded it to brushless modern electronics and went with a 1S LiPo to power it. When I was searching for an ESC for it, I discovered very few ESCs were compatible with only a 1-cell LiPo. I had to look far and wide before I ended up buying a Turnigy TrackStar One Cell Gen II ESC that WAS compatible with 1S LiPo, and it wasn't cheap. Your ESC may well not function properly on 4.2V. One generic ESC I tried before buying the Turnigy didn't work at all, though it was getting power. The problem is, the voltage was lower than the low-voltage cutoff for a 2S LiPo battery, hence it was in emergency shutdown mode. I probably could've disabled the low-voltage cutoff but running any LiPo battery like that would be pretty foolish and dangerous.

https://www.rc10talk.com/viewtopic.php?f=37&t=35541&start=108

[jwscab]

yeah, that is likely the problem is that you are cutting out because of the 1S. the tekin esc I think can run on 4 nicd cells, or 4.8v, and if you use it in that mode, you need to tie the two red wires together(if it's got them) to bypass the regulator.

as coelacanth mentioned, running 1S is a little tricky.

[rraeford]

Thanks everyone. This is exactly what I was hoping to hear. I am not stoked about having to buy a new esc but at least I know know what to do.

[rraeford]

Did some looking for 1S esc and found a few. Unfortunately, they’re either $179 or less expensive ones are out of stock everywhere. I found voltage boosters aplenty so I am trying one of those. I am hoping this will solve the issues.

[jwscab]

Voltage booster should work.

[rraeford]

Fixed!

[Coelacanth]

Fixed!

How was it fixed, with a voltage booster? A 1S ESC? Your solution may be helpful to others having a similar problem after finding this topic.

[rraeford]

With a voltage booster.