Senton Senton 3S slowed after running through the grass just fine.

slick2500

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Thanks for the tip. Just curious, what is the importance of running down to 3.4v per cell prior to charging it? I'll try this this weekend on both batteries. It may be premature but I am hoping the issue was just with that mAh limit that was too low by default.
Because you want to apply the longest charge you can and you really do not want to discharge the battery below 3.4v per cell after 3.2v the cells start to get damaged. Also when charging during this do not charge above 1c.
 

Dulb_D

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Because you want to apply the longest charge you can and you really do not want to discharge the battery below 3.4v per cell after 3.2v the cells start to get damaged. Also when charging during this do not charge above 1c.
Ok, yeah I always only charge at 1C and never discharge them below 3.6v - that's when my LVA kicks on.
 

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The SMC 8000 mAh 2S battery arrived this morning. The charge when it arrived was roughly 3.8x volts. Balance charged it and it came out as shown in the image.

3177 mAh input
79 minutes
4.198V in one cell, 4.195V in the other cell

Our charger only goes to 7A so was less than 1C charge rate. Am going out now to test it and see what happens.
 

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Bri26

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One thing to consider is that a 2S 8000 mAh LiPo battery can weigh quite a bit more than one that has a lower mAh. In general, more weight can be more of a strain on the motor and the drive train.
 

Dulb_D

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The SMC 8000 mAh 2S battery arrived this morning. The charge when it arrived was roughly 3.8x volts. Balance charged it and it came out as shown in the image.

3177 mAh input
79 minutes
4.198V in one cell, 4.195V in the other cell

Our charger only goes to 7A so was less than 1C charge rate. Am going out now to test it and see what happens.
Just out of curiosity what do you have the charge mAh limit set to - assuming it has this setting? I had noticed on my charger it was set to 5000mAh so neither of my batteries were ever being fully charged... not sure if you read that post I did a few days ago.
 

jrude

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Just out of curiosity what do you have the charge mAh limit set to - assuming it has this setting? I had noticed on my charger it was set to 5000mAh so neither of my batteries were ever being fully charged... not sure if you read that post I did a few days ago.
I saw your post about that before and when I did, I re-read the Venom Pro 3 manual like 4 times, and I never saw anything in it that I could figure was the same setting. It is the Venom charger p/n 0684, link to manual is below.
https://system.na3.netsuite.com/core/media/media.nl?id=1797781&c=1327152&h=3153a9b0f61f18062e22&_xt=.pdf

The manual says whatever the battery capacity is, divide that by 1000 and that is the current setting for 1C. The battery is an 8000 mAh so the current should be 8A, but the charger only goes to 7A, so really I charged it at 7/8C.
 

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It's the Capacity Cut-Off option under User Set Program I believe. Look at the top of pg. 9. See what that is set at.
 

jrude

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One thing to consider is that a 2S 8000 mAh LiPo battery can weigh quite a bit more than one that has a lower mAh. In general, more weight can be more of a strain on the motor and the drive train.
Understand. I weighed both batteries on my shipping scale, the 5200 Lectron was .58 lbs and the 8000 SMC was .74 lbs. That's not really that much, and I suspect the tall grass I was running it in has a lot more drag.
It's the Capacity Cut-Off option under User Set Program I believe. Look at the top of pg. 9. See what that is set at.
Right there on page 9... :)

It was set to 10k mAh
 

Bri26

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It's not crystal clear but I always took that setting to mean that it's the most capacity it will add to the battery during one charge. Since the battery starts with at least half the rated capacity then it should charge it all the way even if the battery is over 5000 mAh. Jrude posted that he charged his 8000 mAh battery and it only took an additional 3177 mAh to get it fully charged. This is because your starting with at least a 60% charged battery.

One way to know for sure if a 2S LiPo is fully charged is that each cell should read between 4.19 to 4.20 volts when the charge cycle is completed.
 
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jrude

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So I ran the truck on the SMC 8000 mAh 2S battery and it lasted for 28 minutes and 34 seconds. I hit the pause button on my phone stopwatch ever time I had a rollover, so I believe the 28.5 minutes is pretty accurate, at most it's 30 seconds over actual, so maybe just say 28 minutes of total run time.

I ran it WOT on 75% speed setting for nearly the whole time. About 95% of the time it was on somewhat tall grass, see picture, the last 5% it was on hard pack dirt. I was trying to keep it on the grass as a worst case scenario and I think I only rolled it 7 times so it was running nearly continuously for that 28 minutes. At one point it was pulling to one side, and when I rolled it, I realized there was a stick stuck in the bottom, so a little extra drag for an unknown period of time. :) It was stuck between the rear control arm and chassis but my hand moved it when I grabbed the handle.

I did not have any shut offs for the first 24 minutes. I felt the ESC and the motor each time I rolled it but they were never hot. At about 24 minutes, it would not take off on it's own for the first time. I turned it off and back on and it took off again, everything was cool still except for the battery wires, they were hot. The EC5/IC5 was not hot, only the wires were hot near where the hold up caps are soldered into the ESC wiring. This was on the grass so I ran it for a few more minutes and stopped it on the grass again, and it would not take back off again. I cycled power and drove it on dirt for a few minutes, and did several stop/starts, and it started moving on it's own again each time on the dirt. Just before the 28 minute marker it started slowing down, probably running at 20% of it's normal speed. It ran like that for maybe 15 seconds and then it stopped. Cycled power and it took off again on it's own on dirt, but it still was 20% normal speed. It ran for 15 or so more seconds and then it wouldn't go anymore even if I cycled power. At that point I just shut it off and hit it with the leaf blower to clean out the insides.

I did have one period of about 3 minutes of down time where something got jammed in the steering servo, I guess I'll take that apart and block off the hole in the chassis under it. I did hit the pause button for that down time but the battery had some time to cool down, although it probably wasn't any significant cooling.

I put the battery in the charger when I got inside and the cells were at 3.00V and 3.16V. Once the battery cools down to room temp I'm going to recharge it so my son can drive it tonight after homework, he got home from school at about 3:30.

I guess it was the battery? The Lectron Pro, more than one time, stopped running in less than 1 minute from full charge. This battery went 24 minutes of pretty high load before it shut off the first time. The top speed on dirt was easily 10-20% faster than the top speed on grass, and it was on grass nearly the whole time.
 

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jondilly1974

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That’s good news. I would suggest you don’t run your cells that low. Each time you defeat LVC you risk damaging your Lipo. I would suggest 3.4vdc per cell as your cutoff. Use a lipo checker when it goes into limp mode and plan accordingly.
 

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I agree with not running them so low, I did not figure they would get much lower than the 3.2V setting in the ESC. Granted this is also our first "real" RC car with a LiPo, the old brushed Dromida had a NiMH.

I do hope the battery is the shut down culprit, I don't want to go replacing parts. At one point I figured it would be better to return it to Amazon and exchange it for the 6s Senton since it comes with the better radio and ESC, given that a 3s Senton + new radio + new ESC would be the same price. I already have the two 2S batteries. It doesn't look like I have to do that anymore.

Thanks
 

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My charger won't even charge a cell below 3.0 I'd never run my batteries that low. Nearly a half hour of mostly wot? Not good. Get a temp gauge and really check those temps next time. Hard to believe the motor wasn't hot after what you described.
 

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My charger won't even charge a cell below 3.0 I'd never run my batteries that low. Nearly a half hour of mostly wot? Not good. Get a temp gauge and really check those temps next time. Hard to believe the motor wasn't hot after what you described.
I guess I don't understand, are you saying it is bad for the car to run for 28 minutes at WOT, or should the run time have been longer than 28 minutes at WOT?

What is everyone's definition of "hot"? Is it noticeably warm? Yes. Did it burn my fingers? No. I could have touched the motor and ESC indefinitely at the temperatures they reached. I design electronics, industrial temp rating is typically 80C, these temps were nowhere near 80C. I can't touch 80C with my fingers.

We are going to run it again probably tomorrow, I'll check some temps with a thermocouple.
I put the battery in the charger when I got inside and the cells were at 3.00V and 3.16V. Once the battery cools down to room temp I'm going to recharge it so my son can drive it tonight after homework, he got home from school at about 3:30.
After the battery cooled down to room temp I checked it on the battery meter, and it was reading 3.18xV and 3.20xV, up from the readings immediately after use this afternoon. It was not done charging though when my son had to drive it before it hit bed time.
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We ran the car again tonight but we ran it on the Lectron Pro battery. I charged it until the charger shut off and beeped, the cell readings were 4.18xV an 4.19xV, but I forgot to take a picture of the charger so I could remember later. :( I was trying to keep up with my 8YO.

After running it for about 2 minutes, it shut off and we cycled the power. Ran again for 5 minutes, cycled power. I think we cycled power like 8-10 times over the course of 20 minutes. Towards the end we only drove it on the asphalt and concrete because the car would not start itself moving in the grass. Once it slowed down and stopped, we shut it of and brought it in. I did not bother to try and time the Lectron Pro tonight. The battery meter said 3.510V and 3.491V when we went in. Later I am going to re-charge the Lectron Pro battery to see how much capacity gets pushed into it.

We also charged the SMC battery that I ran this afternoon. However, I left it charging and we went out to drive the car, and when the charger beeped, my wife hit the stop button so I did not get to see the results at the end of the charge. However, before we went out, it had charged for about 90 minute and it had just over 7700 mAh of capacity pushed into it, so I suspect it got a pretty full charge even though I could not see the end result.

Anyway, it's looking like the Lectron Pro is the problem.

Also, I ordered one battery from SMC but they sent me two. I emailed them to ask what they wanted to do, but I'm thinking we are going to keep the second battery, I'm just waiting to hear back from them on what resolution they want.
 
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jondilly1974

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Everyone has a different finger sensitivity. Buy a $10 temp gun. It will tell you acutely what your temps are.

That said, he was surprised you would be able to run WOT for 28 mins without thermal. That is quite an accomplishment. Not normal.
 

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It was on the 75% speed limiter when it did 28 minutes of WOT, so not truly WOT I guess. I was trying to replicate the previous failures and also figure out how long this battery will last for my son on Friday. Friday is his first day of RC cub and the car has to run for around an hour.
 

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It was on the 75% speed limiter when it did 28 minutes of WOT, so not truly WOT I guess. I was trying to replicate the previous failures and also figure out how long this battery will last for my son on Friday. Friday is his first day of RC cub and the car has to run for around an hour.
Wow, an hour of running? For me that's 3 batteries worth of juice. I don't like running anything bigger than 5000 mAh for a few reasons. I don't like the size and weight of the larger packs. The other thing is I don't like discharging large capacity batteries if a breakage ends a run early. It takes forever and I have a decent charger.
 

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Yes, track time is one hour, but with rollovers and crashes and conversation I don't see him driving for a full 60 minutes.

I bought the big battery because I didn't really want him taking it apart too much while 20 of his friends/peers are poking around. However, at 75% speed, which is probably what he will want to run, I think he will end up changing the battery during the track time anyway. Also, he has gotten good enough at disconnecting the EC5 connector now that I don't think it's a problem anymore. At 50% it might make it on a single battery (the 5200 went almost 45 minutes on 50%), at 100% there will be lots of crashes so he likes to stay on 75%.

Also just charged the Lectron Pro 5200. It took 4658 mAh in 82 minutes.
 
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