long lost newbie lipo questions

[andrewhendler]

mah is important to know to keep your amp draw to a reasonable level on your lipo packs, if you pull to many amps you run the risk of destroying you batts and motor, the esc's you guys are running can pull some pretty high amps. Especially if i am reding correctly and know what size motors you guys are running, a 2215 will not handle 100 amps at all, most of the smaller crawlers I see runnning have motors that will not handle over 25 amps.

As with the mah lipos have no memory so long as you keep them in the nominal voltage range, lipos need a minuimun of 3v or below to damage the pack or 4.25 or higher per cell

Now the mah also gives you the maximum discharge rate for a pack, lets say you have a 2000mah pack rated a 20c. In theory your maximuim continued discharge rate would be 40 amps probably with a max burst of 5 seconds. Anything over that and you risk damage to the pack.

[JohnRobHolmes]

The mah and C ratings are guidelines for a pack that are not always correct. 25 amps at 10v is a lot different than 25 amps at 9 volts, but both packs may take 2100mah of charge. Even a cheap 1000kv 2215 will burst 50 amps on a nice 3 cell lipo. If the Lipo isn't good quality it won't deliver, and the cell life can be decreased from consistent voltage depression. ESCs are merely the power channeler.

[andrewhendler]

Originally Posted by andrewhendler

Now the mah also gives you the maximum discharge rate for a pack, lets say you have a 2000mah pack rated a 20c. In theory your maximuim continued discharge rate would be 40 amps probably with a max burst of 5 seconds. Anything over that and you risk damage to the pack.

sorry john, it was late, I meant to say 40 amps with a maximuim burst of 80 amps

[JAM MaxAmps.com]

John i'm not sure what it was I didn't save the chart. I have the pack charged up and I'll toss in the data logger and run it until the pack dies. I'll post the runtime and the chart when finished and then do a 3 cell 1550 or a 3 cell 2100 to show the differences.

Be back latter.

Jason

[andrewhendler]

That would be helpful Jason, also can you list what motor and speed controller your running. I have a bunch of different motors lying around and bolted to planes i am going to start testing, including some hackers and axi's and there chinese clones as well.

[JAM MaxAmps.com]

Ok I laid a beating down on the Holmes Hobbies Crawlmaster Sport outrunner and the 860 mAh 11.1 volt saddle pack. I don't think the Crawlmaster like it to much It stalled twice and got up to 120 degrees.
Anyways here's the results I ran it to almost 20 minutes when I took the motor temp and stopped. I used only 566 mAh from the pack. The saddle pack was cool to the touch after the run. High amps was 66.57 and high watts was at 505. I think those spikes came when the motor stalled. I'm charging the pack right now to confirm how much was used by seeing how much I put back in. You can see the graphs here:http://www.nitrokillers.com/showthre...=3940#post3940

Jason

[andrewhendler]

Thanks Jason,

John,
do you have any other specs for yur motors than whats on your site?

[JAM MaxAmps.com]

The pack just finished and I put back in 560 mAh's so we are right on track there. Now remember I was driving this thing as hard as I could in the house on pillows and such and I guessing that under mormal conditions one would see 30 to 35 minutes of runtime from this saddle pack.

Jason

[JohnRobHolmes]

Can you get some voltage data? From my calculation the battery is falling to 7.59V under the big 66a spike. You need more battery for the motor, it shouldn't get under 9.

[JAM MaxAmps.com]

Those big spikes are when the motor stalled which happened towards the end of the run and the AX-10 was on my wood kitchen floor. No load. I think that hard running for alomost 20 minutes got the motor to hot and that's when the spikes happened when I tried to go full throttle from a dead stop The motor just bound up and the crawler barely moved. It was 120 degrees when I stopped. As I said the pack was cool and I think under normal crawling the motor will be fine. I was just trying to see what the highest amp peaks would be and wasn't expexting the motor to do what it did. The voltage data is in one of the graphs that I linked to. And it did drop to 7.5 volts. I'm gonna run the 55T lathe motor for the same duration in the morning and will post the results.

Jason

[JohnRobHolmes]

Originally Posted by JAM MaxAmps.com

Those big spikes are when the motor stalled .....No load.

I am a bit confused here. No load stalling?

[JAM MaxAmps.com]

No load, the truck was on the wood floor sitting there at the end of this run and I floored it to do a run down the hall and the motor just hung up and made the rig just jitter and barely move. Once I let off And did it again it went.

Jason

[andrewhendler]

was the motor cogging when it did it?

[JAM MaxAmps.com]

No cogging at all It just acted like some had a pair of pliers on it and wasn't allowing it to spin free.

And here's the results from a 55T lathe motor with the same 13T pinion and the 11.1 volt 860 Saddle pack.

Lowest voltage was 9.2

High Amps was 35.32

total mAH used was 644 in 20:49.5 minutes

Motor temp was 110 degrees

esc was 80 degrees

and saddle pack was 74 degrees

Graphs are below.

The low volt spikes and high amp spikes were made by holding it back and making the tires dig and spin on the carpet. The not so high spikes where while pushing a large leather foot rest across my living room. The rest was full throttle shots over pillows and up the plywood sheet with the 2X4's screwed all over it. Same driving as with the Crawlmaster in it. The run was flawless no problems at all considering how hard I was driving it around.

Jason
Attached Thumbnails

__________________

[Reflection]

Personally,I feel it's not a good comparison between the 55t and a Crawlmaster. Two totally different apples IMHO.

[JAM MaxAmps.com]

I'm not comparing the motors I'm showing what our new 11.1 volt 860 mAH saddle pack can and will do. John said that the pack couldn't handle the motor and this shows that it can. Andrewhendler wanted to see how the packs performed and I simply showed him with a couple of different motors. I'm not trying to bash on John's Motors at all so please don't make it sound like that. I've said in other posts that I like it and it has great power for regular crawling but under the 20 minute constant hard run it had issues that the 55T lathe motor didn't have.

Jason

[JohnRobHolmes]

Originally Posted by JAM MaxAmps.com

No load, ... I floored it to do a run down the hall and the motor just hung up and made the rig just jitter and barely move. Once I let off And did it again it went.

Jason

Originally Posted by andrewhendler

was the motor cogging when it did it?

You describe cogging Jason, and it was caused from too low of a pack voltage.

Originally Posted by JAM MaxAmps.com

John said that the pack couldn't handle the motor and this shows that it can.

I stick to my statement. If the motor "jittered" under full throttle the pack is not enough. It may work for a 55t brushed motor, but you have proven that it does not work with the Crawlmaster. The Crawlmaster needs more battery power.


What voltage cutoff are you using?

[andrewhendler]

jason,

It sounds like you have some resources for batts, anyway could I talk you into trying the test with a 3s over 1500mah

[JAM MaxAmps.com]

Look I,ve been using brushless motors for years I know what cogging is and it wasn't cogging. Fire up and out runner and grab the bell with your hand now squeeze as hard as you can. Basicaly allowing the motor to still turn but not fast. Like some one had a drag brake on it. That's what it did and you'll notice in the graphs that those times are the only time the voltage dropped. It wasn't the pack as you can clearly see that the voltage never drops that low until the motor basically froze. It didn't lurch it didn't jump it did not cog like brushless mototr do. Another way to describe it was like having a bearing going bad and draging. Oh and LVC is at 9.6 volts. And John considering you didn't see or hear what it did you really can't make any claims as to it being the batteries. if the pack couldn't handle the voltage it would have been coging from the start just like any other brushless motor that is over powering a pack. Anyone with Brushless motor knowledge knows that they will do it all the time rather than just once or twice and being that it was on a bare floor that the tires slip on shows that there wasn't any hard load on the motor. I think the motor couldn't handle the heat and the hard running. God forbid it be the motors fault. Geeze. What's the problem you don't like seeing test results from other people. Get used to it. I know from experience, it comes with the teritory. And as said this wasn't about the motors it was about how well the saddle pack worked and runtimes. I just posted up the facts and they show that God forbid the Crawlmaster sport had an issue where as the 55T Lathe motor didn't. Here's all the graphs.

Jason
Crawlmaster SportAttached Thumbnails

55T Lathe motorAttached Thumbnails

Like I said The High spikes with the 55T Lathe were made by Holding the AX-10 and making it dig into the carpet and pushing a foot stool across the floor. The High spikes on the Crawlmaster were on a hard wood floor full throttle starts no load on the AX-10.

Andrewhendler I hope this info helps you out.

Jason

[JAM MaxAmps.com]

I'd be glag to 3S 1550 And 55T lathe coming up. Then we'll switch motors and go again.

Jason