3S battery in Revolt 30

[nammer]

Hi all, I'm a super newb to RC boating. I just got a Revolt 30 last week that came with a 3s battery. Let me explain my situation and please correct me if my understanding is wrong.

so it is recommended the revolt 30 uses two 2s batteries or a single 4 S battery

I am using an onyx 235 balance charger, and when i charge it to full it comes to about 4.2 volts per cell

I took the Revolt out on the pond today, ran for about 4 min, I saw it noticeably slow down in speed, but i wanted to keep running it to see how long it would run. then all of sudden it died immediately. I got it back (after waiting for the wind to blow and using a styroam life saving ring) and put the battery on the charger, it's at about 3.9 V.

could it be that the boat needs between 3.9X3 = 11.7 V and 4.2 x 4 = 16.8 V to stay running?

[fox88gt]

Hi nammer,

Welcome to the forum. First off, I'd recommend dowloading the Revolt instruction manual from this link and reading Grimracer's battery tips: http://manuals.hobbico.com/aqu/aqub24-25-manual.pdf

Here's what happened based on what you've told us - Essentially you ran the battery down way low (slowed down), then hit the Low Voltage Cutoff (LVC), stopping the boat completely to prevent damage to the battery. Essentially, you seriously over-discharged your battery. Sounds like its taking a charge again though. Running even a bone-stock Revolt on 3S is going to put on hell of a demand on that battery. 4 minutes sounds about right to use up all the juice in that battery. I would highly recommend at least a 40C rated 4S pack for the revolt. Your battery won't last long being abused like that. Serious damage can be done to the battery and possibly the boat by doing that. 4.2 volts per cell is where you should be when the battery is fully charged.

Jeff

[nammer]

hey jeff, thanks for your reply, I'm a little confused at your comment,

so you mentioned me running my battery really low, I do agree that sounds like the reason, but when I was charging it, it was still at 3.9V per cell, i have read that each cell can go down to about 3.3V or 3.6V before being low (based on who you ask) I am basically asking, do I not have enough voltage because I only have 3 cells versus the recommended 4.

[nammer]

and thank you for the pdf link, i saw that the ESC have a voltage cutoff of 10.8V

[tlandauer]

Wait the minute, do you have the stock AC ESC??!! The Low Voltage Cutoff is 11.6v not 10.8v! That ESC will not work with any cell count that is lower than 4s, I am surprised that it let you even calibrate. So yes, it will slower down if total voltage is below 11.6v! But with only 3s, you will not have the correct cell count and voltage for the ESC to read it correctly.
Some ESC, like HobbyWing's SeaKing will allow 2s-6s use, as far as I know, the AquaCraft is designed to only use with 4s.
You battery is not damaged, you just need to get a single 4s or two 2s to hook up in series to make it 14.8v.

[nammer]

hey there tlanduer, yea just relooked at the pdf, you are right, it says low voltage cutoff at 11.6, but i read the 10.8 here, just a misprint?
and yea, I will be getting a 4s, this was my 2nd outting with the boat, so now I know tons more about batteries!!! thanks for your help guys

Low Voltage Cutoff: 11.6V

PLEASE READ:
Notes about using LiPo batteries in your boat: The Revolt uses
the AquaCraft 60amp motor controller. This controller has a built
in stutter bump system that cycles the power to the motor when
the battery voltage reaches 12V. This is designed to warn you of
impending low battery voltage and subsequent shut down. It also
has a 10.8V battery cut off safety system that shuts the power
down to the motor to avoid damaging the batteries.

[nammer]

and yes it is still the stock ESC

[tlandauer]

It can not be 10.8v, that is 2.7v/cell, battery would have been damaged!!!
In order for the ESC to read cell counts, it relies on total voltage. A 4s lipo has a 14.8 v ( storage volatage @3.7v/cell) , but a fully charged, fresh off the charger reads 16.8 volts. That is 4.2v per cell.
Your fully charged 3s is 12.6v, since the ESC's low voltage DETECTION is set at 11.6v, when you plug in your fresh off the charger 3s lipo, it is possible that the ESC is fooled to think that is still a "partially charged 4s" and therefore lets you run a bit. But this quickly changes and now you enter LVC mode.

[tlandauer]

I think it just tells you that at that voltage, it is off, it will not feed anything to the motor. Note that at 3v/cell is already considered potentially harmful to lipo, LVC is set at 3.3 or 3.4v sometimes.

[nammer]

thanks for the info, sorry, I just have one more q, I always thought mah was the capacity/how long it will last/how much gas in the tank, but when i'm charging, I basically look at the voltage before and after. Would the higher the mah make the voltage last longer? The battery I have is a 6400mah and I was still able to get about 4 min of mixed usage, and I'd say my battery is still about 3/4 full? thanks

[tlandauer]

You are right, higher capacity means longer RUN TIME, and since you have a longer run time, that means the RATE the voltage is dropping is SLOWER than a smaller capacity battery would have.
Your charger should let you know how many mah is being put back to the battery. I prefer to have at least 30% capacity left in my battery after running my boat, so a 6400 mah battery should have 1920mah left in it, your charger should be able to charge back 4480 mah.
In any case don't run below 20% capacity.

[SloHD]

You're correct mah is the capacity. And yes more mah makes the voltage last longer.

Have a look at the following link, and read, read, read. Once you get used to them, it's very simple.

http://www.rchelicopterfun.com/rc-lipo-batteries.html

[nammer]

yea my charger is only putting in less than 2000 mah,

thanks for the link slohd, def gonna read it now

thanks for all the info and q's answered everybody!

[rickwess]

From the manual on the stock ESC:

Stutter Bump Voltage: 12V
Low Voltage Cutoff: 11.6V

Unless you time your runs, relying on the stutter bump is not good. 3V per cell is into damage territory. Either time your runs or get a ESC that you can program for the "stutter" at 3.2V per cell.

[nammer]

yea you're right, when i get the 4s battery, that would be a problem, so I'll do some trial and error with timing and charging