Real current draw on a Mamba Max 5700

[GSMnow]

I took my car over to RTR Hobbies today to do some testing to see why my LiPos are getting hot. They have ordered me an Eagle Tree e-Logger V3, but it is not in yet, so we hooked up an Astro Watt Meter and had a little fun. I put on my totally bald tires I use for street running. The shop owner ran the transmitter and read the watt meter while I loaded the tires on the sealed asphault parking lot. This was not easy to do, the car really wants to rip out of your hands and the slipper clutch was too loose to get a true max, but this is what we did get. Voltage was still over 7 volts, but was jumping a bit too muh to get a solid 10ths. Current was as high as 78 amps for a few seconds or so. It would surely pull more if the slipper was not letting go. And all four tires actually started to smoke a little. It left dark patches on the pavement. This is a real world 546 watts. With the tires hooked up and pulling across the ground, it could even pull more, especially with the slipper tightened. I loosened it at the race on Tuesday night because I heard the belt skip. I think I went a little too far. When the tires grabbed the ground, the slipper totally let go and the current fell to just 30 amps. That seemed odd. When I let the tires spin up again, I was able to re-load it back over 60 amps with ease.

RTR Hobbies is a new shop here in Santa Clarita. Their main focus is on flight, but since they are huge into electric flight, they have more brushless and LiPo stuff on the shelf than anyone, and they are getting more and more car stuff. They are getting me a 20C constant 30C surge rated 2S 4300 LiPo from their distributor. With a constant 86 amp rating, it should handle the current better than the MaxAmps 3000's 60 amp constant rating. They don't have final pricing on it yet, but they should beat the Max Amps 4000 price. They have a whole pile of 3S stuff in stock. No one flys on less than 3S. Too bad I have to run 2S to be legal. A 3S 2200 would actually be more power than my 2S 3000's.

[TheSteve]

Those numbers do seem a little high. I don't think you can really use them unless you drive the vehicle.

I have a wattmeter installed in my Losi jrxs with 3S LiPo with a mamba 5700.
I have been able to get it to show 100 amps but it was work. Only by getting the tires warm and hammering on it from a dead stop does the amp draw get that high.
We also installed it on a touring car with 2S LiPo and a Mamba 6900, highest amps during race conditions on a big track were mid 60's.

I use this wattmeter -
http://www.western-robotics.com/inspector_watt.html

[GSMnow]

I will post real race results when I get my Eagle Tree system. What really got me going was when I pulled my car off track during practice and the Max Amps 2S 3000HV pack was abut 160F. OUCH! It is rated at 60 amps continuous which would be depleting the pack in just 3 minutes, yet I get a 12 minute run time out of it. The theory is that I am exceeding the 30C 30 second surge rating each lap. If you run 30 seconds at 30C, you need 3 to 5 minutes for the pack to cool again. Instead I am hitting 30C for 4 seconds, every 27 seconds, not allowing the pack to cool. The real answer will be told by the Eagle Tree. If I rarely exceed 20C (60 amps) then my packs are not making their rating. They certainly are putting out 60 amps, while still holding over 7 volts. That is impressive, but they should not heat up and start to puff in a 12 minute discharge. So I think I just may be topping 90 amps down the straight.

[GSMnow]

A quick note...

The guys at RTR also suggested raising the LVC point to 6.6 volts. It does seem my big heating happens right at the end of the pack. When I stop at 8 minutes or less, the pack has not been over 130F. Maybe the internal resistance of the cells climb when they are below 25% capacity?? That would make sense, as I have only seen over 140 when I drive to LVC. So I just set it to 6.6 and we will see what it does next time out. It will lop a minute or more off of run time, but that is not an issue.

[vashon10]

I can't really comment on the amp draw, but it reminded me of an interesting video with an eagletree. I have no association with truerc or anything about them, just found the data interesting.

See last two vids on this page.....

http://www.truerc.net/canada/shop/videos.html

[ElectricThunder]

A quick note...

The guys at RTR also suggested raising the LVC point to 6.6 volts. It does seem my big heating happens right at the end of the pack. When I stop at 8 minutes or less, the pack has not been over 130F. Maybe the internal resistance of the cells climb when they are below 25% capacity?? That would make sense, as I have only seen over 140 when I drive to LVC. So I just set it to 6.6 and we will see what it does next time out. It will lop a minute or more off of run time, but that is not an issue.

I've noticed that with my 4500mah 2s lipo, if I stop at a point maybe 10-12 minutes into the run, the battery isn't too terribly warm (maybe 110F max). If I run it until around cutoff, which is 6.4v, it gets to around 125F or 130F.:eek::huh:

I know lipos like to warm up a little to discharge higher current draw, so maybe, towards the end of the pack when the battery's capacity is drained to about 1/4 of what it was at full charge, the C rating is the same, but since it's only a 1/4 of whatever capacity it was, the current rating is actually lowered, and as a side effect, the battery will warm up to speed up the remaining chemical reaction (since a given capacity lipo can discharge X amount of amps for 10 minutes, or 10X amount of amps in one minute for example) in order to produce the necessary current being asked of it?:teacher::huh::huh:

[GSMnow]

That was a fun video, trashing that poor car in the sand. I think he needs to work on the suspension a bit. It should not flip that easy.

I don't know how the chemistry of LiPo cells works. It may be possible that some of the surface area of the plates losses it's ability to produce current, so the remaining active surfae area must work harder? When the cell is not under a load, it would then make sence that any remaining energy in the cell would tend to disperse evenly through the cell. Obviously, the cell heating is not a problem at low drain. I just don't know for sure. I can't wait to get the eagle tree. I have so many things I need to test with it. I will also have to order a few other sensors.

[SS Pede]

90 amps down the straight seems like an awful lot. I will be very interested to see what the Eagle Tree records.

I do think it is possible you are over-drawing those 3000 packs a bit. It seems that, given the relative lack of standards associated with LiPo technology, it is possible to get a pack that will not truly support its rated current draw. Someone has suggested to me that maybe the cells can put out 60+ amps but the internal connections within the pack cannot necessarily support that. Who knows. Certainly for all the hype I would expect even a relatively low-capacity LiPo pack to be fine for many powerful motors (after all, who really draws even 60 amps continuous?). I am looking forward to seeing your data.

[GSMnow]

I don't think the heating is from a connection problem. The cell tabs are both at the end where the wires exit. The pack wo no hotter in that area. In fact, the hottest spot on the cell was a bit more than 1/2 way back from there. It actually seemed like a local hot spot. Most of the pack surface showed under 145.

[Ball Racing]

I pull enough current with a max amp li-po to regularly melt the heat shrink off at the deans in one battery pack run, in a clod with two 10 turn brushed.

I guess thats amp draw................ Motors can still be 140-150 max but wires are HOT

[GSMnow]

With my LVC raised up to 6.6, the pack only got to 135 when I ran it hard to the LVC point. It shortened the run from 13 miutes to about 11. It also hung on at 6.6 and I could do 2 laps as it lost response, but the kept running in current limit. WIth the LVC at 6.2 volts, the car would stop dead, and not roll again until I let it sit for a fair time. The 6.6 LVC seems much nicer to the batteries.

If you are melting the shrink wrap at the Dean Ultra plug connector, you are not only pulling huge currents, you probably also have a poor connection somewhere. All of my Deans Ultra connectors run cool.

[Ball Racing]

I am pulling TWO motors off one plug

[ElectricThunder]

In series or parallel?

[GSMnow]

I found a site somewhere, that listed amp ratings for many popular connectors. They listed 60 amps constant on the Deans Ultras. That seems fair as they claim the same or just a bit less resistance than a #12 awg wire.

What gauge wire do you have coming off of the plug on each side?
And what capacity pack are you running? Mine are just little 3000HV's. 2S is only 10mm thin. I went with these due to a very odd low cost per watt hour. And the fact I can stack two in my truck and run for well over 20 minutes on the 2S2P 6000mAh setup. If I had more packs, I would probably just run it that way for the amp capability. I usually have less than an hour between heats though, so I need at least 2 complete setups for the car. In the XXX-4 I will need to grind a few "features" of the chassis to hold the full thickness of the 6000 setup. A 2S 5000HV will probbaly fit with a pad under it still, without hacking the chassis. The bumps that hold a stick pack and locate the side by sides hit the LiPo in just a few small points, and I am very concerned how it will effect them if it dents in at those points. I may have to do some grinding for the hard cased packs as well, except maybe the Orion 3200 Carbon Edition that is shaped like a stick pack.

[Ball Racing]

I run 6,000 mah, and sometimes a 8,000mah
run wet noodle 12 g on the controller side,
Motors are wired so the controller sees it as a 5 turn..

9.5 lbs truck though, 540 cans . lots of tration, short course, lots of braking too,
thats what sucks amps up...

[ElectricThunder]

I run 6,000 mah, and sometimes a 8,000mah
run wet noodle 12 g on the controller side,
Motors are wired so the controller sees it as a 5 turn..
9.5 lbs truck though, 540 cans . lots of tration, short course, lots of braking too,
thats what sucks amps up...


Parallel wiring, so in that case, yup, amp draw is going to be double. Sounds like fun.

[TheSteve]

I pull enough current with a max amp li-po to regularly melt the heat shrink off at the deans in one battery pack run, in a clod with two 10 turn brushed.

I guess thats amp draw................ Motors can still be 140-150 max but wires are HOT


Personally I'd have to say there is something wrong with your deans connectors or solder connections if you're doing that.

[Ball Racing]

Could be,
but it has happened for last two years, and on 5 trucks,
6 or so batteries (all li-po)
and a dozen or so deans...
But there are twin 9 turns in there some times too,
along with about 25 plus degrees timing...









It's a race clod thing...................

[ElectricThunder]

That's a helluva lotta timing.

[GSMnow]

OUCH!! are there rules against running brushless? A pair of SideWinder 4600's on 3S would be so much more fun. What does a racing CLOD end up weighing and what sort of top speed do you need to hit? What is the drive ratio from the motor to the tires, and the tire dia.? I bet a 40 mph CLOD would sure be a handful.

[Ball Racing]

I had a 40 mph set-up 4 s li-po and 15 turn brushed.
I have also a mamba 7,700 set up clod.

Tires are 6.2 high
trucks from 8.5 to 9.5 lbs

Motor on font axle,
motor on rear.

Thats what kill the 540 can motors,
you have enough power to pull a wheely, then all the load stays on one can...

25 mph is all you really need for most courses..
But most of mine go 30 mph on pavement. according to GPS

[sixshootertexan]

I was pulling 185amps on my dragster with a 7700kv motor. I had a Thunderpower 3s rated at 108 amps. The voltage dropped to 5.8 volts. We were doing speed runs at a local 1:1 drag strip. I had ran it for about 2.5 seconds. Hit 78 mph. Got a Flightpower 3s on order that is rated at 270 amp burst, 135 amp continuous.

[GSMnow]

So you plan on running the 7700 on 3S?
I hope you have a scatter shield around it ;-)
7700 x 11 volts = 84,700 rpm
It may live for a drag run, but wow!

what is your goal? top speed? time to get there? What does it weigh?

Are you rules limited, voltage pack size, etc?

If there were no rules, I would suggest a larger can motor, like a Neu 1515 or for a budget, a Feigao XL can, and then run it on 4S with a BEC to run the radio gear. If the motor must be a 540 size, the MM4600 on 4S would be a screamer. 64,000+ rpm, and double the watts of the 7700 on 2S at the same current. 120 mph should be possible with proper gearing and no regaurd for being able to do it again ;-)

[sixshootertexan]

This is the numbers on the 7700kv.


with Thunderpower 2200mah 110amp burst rate
1223 watts
184.40A @ 5.93V

with Flightpower 4500mah 270amp burst rate
1581 watts
185.06A @ 6.41V

[GSMnow]

I posted this under the thread "Got my data logger"

My MM5700 on 2S
The highest I saw actually driving the car was 360 watts.
58 amps @ 6.2 volts

Holding the car back to get more load, it did hit 78 amps at 6 volts even. I didn't want to load it any harder, and the LVC in the Mamba Max was cutting in and lowering the current draw to hold 6.0 volts.

At 40 to 50 amps, the slipper clutch let's go, and the tires were breaking loose. The XXX-4 is just too light to hold any more power with it geared for this tightish track. Top speed is just 35 mph (a bit more due to tire growth) but I can just barely reach that with a perfect line onto the main straight, so there is no use gearing faster for this track. I drag raced a couple of the fastest cars, and in each case, we all stayed within a foot for the whole straight as we were all at traction limit on the dirt.

[GSMnow]

I got a chance to do a few more tests. I ran it with both a single 2S 3000 HV pack, and with both of my packs in parallel for a 2S2P 6000 setup.

With the packs fully charged, the calculated resistance did drop from 0.021 ohms to just 0.017 ohms with both packs. Remember, this figure includes at least a foot of wire, and 2 deans concectors. I did the math at several places in the data log.

I topped 370 watts until the slipper and tires let go again. Runnin with the 2P was very good, but I am still not sure that i was really getting all the power the Mamba Max can give. I got the motor up to 180F, the ESC to 140 F and the LiPo pack was only hitting 120F, about 25F cooler than a single pack. I ran for 12 minutes, and pulled it off of the track. The 180F motor was the biggest concern, but I do think the Mamba Max motor can take it, your fingers really can't. The mid motor position really limits the air flow over both the motor and battery. I tried to tighten the slipper, but it seems it is as fast as it was on the 1P pack a few weeks back. The total pack (2S2P) was fully charged as were my best NiMh packs. Voltage just slowly dipped as time went on. The resistance held very close to 0.020 ohms through the run. Voltage after 13 minutes of hard track driving got the resting voltage down to 7.2 volts, they bounced back to 7.662 volts and took just over 3200 mAh to top back off. That seems about right as I could get 12+ minutes on a single 3000 before LVC cut in, but the odd thing was the Eagle Tree only calculated 2200 mAh used in the run. Where did the other 1000 mAh go? I know the batteries are not 100% mAh in to mAh out, but 33% energy lost seems pretty extreme. Obviously, quite a few watt hours went into heating the batteries, that energy is not measured. And all the losses from the 0.017 ohm loss went away to heat as well. I will have to check the calibration of the logger to make sure it is right. It may be under reading the amps a little. At 70% charged, the voltage at 50 amps was holding over 7.0 with the dual packs, compared to 6.2 volts for a single pack. It sure showed on the track, as it pulled harder further down the straight. The extra weight of the second pack was noticeable, but it is still lighter than an EP4200 pack. I need to adjust the suspension a little, the back was bottoming on the larger table causing it to nose down as it went airborn. On several laps I had to pull full trigger to get it far enough from vertical to not end over. I changed my roll up a little to reduce it, but I had to be careful.

Early conclusion...
I never saw over 70 amps on course. The track was not in the best condition, it was rutted and dusty, so I was not at max grip potential, but I can certainly say, the SideWinder would be enough ESC to run virtually any 1/10 setup on this track. Batteries are the key to performance, no matter what you run. With a single 2S1P 20C rated 3000, I cuold only get spikes over 300 watts as the voltage was dropping and the LVC was kicking in. With the two together, making basically a 2S 6000 pack, I saw a solid 370 watts several times before the slipper clutch and/or tires spun, and the voltage was never even close to LVC, even after the 13 minutes of very hard driving. I think I need to test the Reedy and Orion LiPo's (I think I could borrow them at the track) to see how they fair. The Eagle Tree is small enough, I hope to smuggle it into other peoples cars for comparitive data as well. I would love to see what the Novak and brushed B44's lok like on a lap. The current trace on mine is all over the map. I found a way to find a lap in there, but it is much harder than I expected. I guess the excitement does effect time perception too. I thought I was spending 5 seconds on the trigger down the straight, the reality is more like 2.5 seconds. but I also hit full trigger for a little over 1 sec at the table tops. If I got out of shap at all on the straight, it looks just ike the big inner table top as I lift to straighten the car, just like the setup between the jumps. Hmmm?

I hope to have more data soon.