Which Neu Motor

I'm having another issue with maxamps and I'm not getting my battery, so this brings more questions to mind.

If the 1515 line of motors are 1500 watt motors, then on 4S the maximum constant current draw on 4S will be about 107A, right? If this is true, then the maximum constant current draw at 5S will be about 85A. This is assuming 3.5v under load and a motor turning about 30K rpm.

If this is right, then on 4S, I'd need a pretty "good" pack to keep up, but on 5S, I don't need such a hot pack to keep up. If this is the case, I could just run the 1515/2.5D on a truerc 5S 8Ah pack (for A LOT less than a maxamps 4S 8Ah pack).

If I decide to go with a 1512, it should be even better yet, because that should draw even less current.

Please tell me I'm right. LOL. If this is alright, I'll make the switch to 5S. The truerc 5S packs are only like a couple of mm taller than the maxamps 4S packs. The truerc packs are just a bit wider and longer, which isn't a problem.

Now I need to figure out what I'm going to be doing with these brand new Kokam 4S packs that I just bought.

[BrianG]

Don't get too hung up on the power ratings. The rating simply means it can handle 1500 watts (~2HP), but will only pull this kind of power in bursts. Just looks at most everyone's eagletree discharge graphs. 100-120A bursts are common, but the average is far less. Unless you plan on pulling a trailer where the motor will be working every step of the way, I wouldn't worry about it too much.

By the way, a motor is not a "constant power" load, so you can't assume it will pull the right amount of current to equal its rated power. If a motor will draw 107A @ 4s, it will draw more as 5s (133.75A using your 3.5v/cell example). If you want to keep the amperage at ~107A but use 5s instead, go up one wind rating (like a 2.5d instead of a 2d).

BrianG,

Man, you're up late. I'm a chronic insomniac.

What I meant was this. If I am running "X" motor on 4S to attain 30,000 rpm, then running motor "y" (a higher turn motor) on 5S to attain 30,000 rpm should result in less current draw, while doing the same work. Is this right?

I wasn't talking about going from 4S to 5S on the same motor and expecting the current draw to go down. If I stay with 4S, I'll probably go with the 2200kv motor. If I go with 5S, I'll probably go with the 1700kv motor (or maybe even a higher wind). Although both the 2200 on 4S and the 1700 on 5S will turn about the same rpms, shouldn't the 1700 on 5S draw less current?

It figures, Mike is out of stock on the 2.5d.

[jhautz]

But what he was saying was correct brian. He could run the 2200kv motor on 4s or the 1700kv motor on 5s. Similar power.... Lower Amp draw.


EDIT: Damn! You got 2 posts in in the time it took me to get one up.

[jhautz]

Originally Posted by AAngel

Although both the 2200 on 4S and the 1700 on 5S will turn about the same rpms, shouldn't the 1700 on 5S draw less current?

Yes. This is the appeal of higher voltage. Same power, less current. Less current, Less heat. (very general statement, but pretty much accurate)

Uh oh, another insomniac. LOL

It's a cryin' shame, but I couldn't sleep with this stuff running though my mind. I'm still going back and forth with myself on the 1515 vs. 1512 issue.

I really like the smaller can motors. I have an 8L in my buggy right now because I love the zip. I didn't like it at first, because due to inexperience, I didn't have it geared right. Now, it flies. Really flies. If I can get the same effect with my truggy, without stressing the motor and save about $50 at the same time, I'd be a happy camper.

I just hope that the Compro will do well on 5S. I've just had it with all of this expensive battery crap. I just ordered a 5S 8Ah pack from truerc for the same price that 4 bare 10Ah cells cost me from maxamps and have you seen the latest price on the 4S2P 8Ah pack? For that price, I'd rather spend a bit more and get the flightpower 4900 that will actually do 20C without breaking a sweat.

And hey, doesn't less current draw for a given capacity also mean more runtime? Wait, this can't be right. Running the 1700kv motor on 5S will give better runtime than running the 2200kv motor on 4S? It's late, and I can't think anymore. Now I'm just rambling.

[jhautz]

Lower amp draw means longer run time, so yes thats correct.

If you think about it the potenetial energy on a 18.5V 8000mah pack is higher than in a 14.8V 8000Mah pack so you should be able to generate the same amount of power for a longer period of time.

[BrianG]

OK, I thought you were using the wattage to determine current based on different voltages using the same motor. Just a misunderstanding. :)

If you run 4Ah packs, but one setup uses a higher voltage and higher wind motor, you could get better runtime. It's all about how much current is drawn over time.

Yeah, I'm up late. I couldn't sleep so I decided to go to work. So, I post here between doing some tasks that I have to wait for anyway. It's gonna be a looong day though: up since ~7AM yesterday, and won't be going to bed until sometime tonight. Looks like I'll be living on caffeine today. The track at my LHS was looking somewhat drivable, so I might try to leave a little early and hit the track with my Hyper 8.

Well, I'm making the shift to 5S. With the truerc packs being the price that they are, it is worth getting controllers that can handle 5S.

jhautz, I saw the way you drive and I know that you like your stuff fast; so if you aren't having problems with the truerc packs, I don't think that I should either.

It's just unfortunate that I just got a couple of 4S 4.8Ah Kokam packs. I suppose that I could try to sell them. They are too tall for my buggy, and there isn't enough runtime for my son to run them in the MGT. Maybe I could just rig them in parallel for the MGT. Heaven knows there's enough room for them on that beast.

[glassdoctor]

Just a heads up on the packs... in hte past the truerc and maxamps cells have been the "same" cells from the same mfg. I don't know what has changed with the truerc cells lately when maxamps updated thier cells. I would assume truercs are similar.. the latest generation.

Just something to consider.

GD, do you mean that in a good way or a bad way? I'm just figuring that if I go with the 5S setup with a lower kv motor, I'll draw fewer amps, so the quality/performance of the pack won't matter as much. Besides, the 8Ah packs that I've gotten from maxamps have worked out well. The 4Ah cells are pretty good. If truerc is using those same cells, I'll be more than satisfied.

[MetalMan]

Right now I don't think any of the True RC and Maxamps cells are the same (or at least anything larger than 2100mah...).

In any case, I think that the truerc packs are at least good 10C packs that will do 15C bursts. If that's right, I don't see any problems running a 1700 or so kv motor on 5S with these packs. This should be a relavtively mild setup in terms of current draw.

Right now, I'm thinking I'll run my 8XL while I decide on whether to get the 1515/2.5D or the 1512/1.5Y.

I got an email from Mike and his opinion was that the 1512 will blow away an 8XL in terms of performance, but he said he'd go with the 1515. I like the performance of my Muggy on the 8XL and the 7XL. If the 1512 will surpass those, the 1515 will be overkill for me.

As it is, my truck weight just under 12lbs. With the 5S pack, it will probably go to 12lbs; but I still have some upgrading to do in terms of getting rid of some metal in favor of carbon fiber.

i've run 2 TrueRC's 5s 4000mah packs in parallel, with a 1512 2.5D, in my 1/8 onroad, and the packs have worked beautifully. my LSP will be running in about a week, and I'll try the 1512 in it, and see how it runs, and then decide if i want a different motor.