Sign in to follow this  
robster959

Current Drain For Stock Can Motors, And Others?

Recommended Posts

Hey all,

Just wondering about how many amps a stock can motor would draw in a "typical" setup. For example in buggy such as a Blitzer Beetler, or something older like a Frog. I know there are lots of variables involved, but let's say ballpark. I'm asking because I was eyeing some cheap lipo packs on ebay. They were 4000mah 2 cells - with these specs.

* Capacity: 4000mAh

* Voltage: 7.4V

* Cells : 2

* Burst Rate : 15C

* Continuous discharge rate: 10C

* Size :145mm x 47mm x 12.5mm

* Weight: 175g

I'm just not sure of how many amps are typically drawn from a stock can motor, or a 27t stock motor.

Thanks,

Rob

Share this post


Link to post
Share on other sites

Do the packs have a balance lead? Are they in a hard casing?

Playing with fire without these 2 things. If the two cells become unbalanced (common with cheap cells) one of the two will overcharge and run great risk of bursting burning plastic everywhere. Similar if they are not protected in a hard casing for use in a car, easily damaged and they will short internally and run risk of catching on fire. I recommend a Li-Po sack for charging and always remove from the vehicle for charging.

Current draw depends on load. Running tall gearing or in grass or soft dirt will add extra load and increase the current draw. Specs of the Mabuchi silvercan here.

Share this post


Link to post
Share on other sites

10C on a 4000 mAH battery equals 40 amps of draw, I don't think you'll ever get that high continuous draw with a silvercan...

Share this post


Link to post
Share on other sites
10C on a 4000 mAH battery equals 40 amps of draw, I don't think you'll ever get that high continuous draw with a silvercan...

At maximum efficiency it won't draw that much. Only 1/4 of the pack's ability. Stall the motor and it will draw double what the pack can supply according the specs at the Mubuchi site. So under great load is somewhere in middle.

Share this post


Link to post
Share on other sites

Yes, I saw that, but normally, you won't be able to stall the motor in a buggy or ST...

And the batt can take 60 amp burst...

Share this post


Link to post
Share on other sites
Yes, I saw that, but normally, you won't be able to stall the motor in a buggy or ST...

And the batt can take 60 amp burst...

May say it can burst 60 amps, but if it's a cheapy who knows for sure. Definitely needs to be a hard casing pack and the 40 amps continuous may even be overstated. Sound more like a lipo meant for a heli or plane and not a car. Cars see more of the burst amps and varying high loads compared to the aircraft that are more steady and lower. Even my really good Intellect Lipo is slightly overstated, but at 4000 mah and 25c (100 amps rating) is still more than sufficient to power my brushless DI under normal conditions. My SMC lipo exceeds it's ratings, but was factory tested before it went out the door to make sure.

If your going the lipo road then spend a little more to get a good one and you'll be happier in the long run. Not to mention safer with less chance of fire in a good pack.

Share this post


Link to post
Share on other sites

Here is a dyno graph that compares the RZ to the stock silver can RS-540-SH. Givin unliimited amperage at 7.2v, the silver can is capable of drawing upwards of 60 amps at startup. From there it will drop down to near zero. This means you will only be pulling over your 40amp limit in the very low rpm for very short bursts. As others have said, you won't be able to pull more than a 20 amp full-run average, even when racing. Besides, you would certainly destroy the motor running it that hard...

BTW: Even with 27T race motors (properly geared Trinity CO27 Pro motors) at our local parking lot races, we only run about a 12amp overal average (~800mah in 4 minutes)...

53697a.jpg

Share this post


Link to post
Share on other sites

I guess to run Lipo, cheap or otherwise, you need to get some sort of LVC or voltage cutoff. I'm not really ready to switch over to a quality lipo setup or cells. It's just that I saw these lipo packs for $30 US for two, shipped. I figured I'd be able to get nice long runtimes in my vintage cars, or boats. Only thing is the voltage cutoff, and the fact that my old lipo charger doesn't do balancing. And I have to solder my own connectors to the pack. It seems like current wise they might be ok.

Rob

Share this post


Link to post
Share on other sites

Current wise they should be fine.

For the low voltage indicator, you can purchase external cutoffs from companies like Novak. You simply wire to your battery connector and plug it into the receiver. Then your ESC plugs into it. When voltage starts getting low, the it starts to interrupt power to the model.

For balancing, you can always purchase an external in-line balancer. You simply connect the balancer between the charger and battery and your good to go. Of course you have to find one that's compatible with the balance tap on packs you want to run. It's still pretty simple...

Share this post


Link to post
Share on other sites

Or, if you want to take a slightly larger risk, run the car until you notice the battery dumping and then stop and charge...

Share this post


Link to post
Share on other sites

I just found an other option other than the LVC - there are Low voltage "alarms" on ebay that are about $5 shipped. They have a buzzer or siren of some kind and flashing LEDs. They plug into the balance plugs, and monitor the voltage I guess.

I was considering an external balancer, but wasn't sure of the price. It seems there are some pretty cheap/simple balance chargers out now. I'm really considering those 2 lipos for $30 now. It seems I wouldn't need much to get them running safely in my buggies or boats. Nice long run times is what I'm looking for with them.

Cheers,

Rob

Share this post


Link to post
Share on other sites
Or, if you want to take a slightly larger risk, run the car until you notice the battery dumping and then stop and charge...

I don't notice any power drop off in some cars with the brushless. The car just stops when it hits the 6.0v cutoff. The video I added with my Grasshopper doing wheelies, the battery lasted about another 90 seconds and it cutout. I'd been driving for over 2 hours previous on the same pack.

In cars with a 540 silvercan and TEU-101BK it lasts ages and no power drop off. I time my run with these, about 40 minutes in a 4WD buggy (4000mAh) and the pack is about 1/2, stop and recharge. There is no memory effect. My charger says what the voltage of the pack is when you plug it in.

Share this post


Link to post
Share on other sites
I just found an other option other than the LVC - there are Low voltage "alarms" on ebay that are about $5 shipped. They have a buzzer or siren of some kind and flashing LEDs. They plug into the balance plugs, and monitor the voltage I guess.

I was considering an external balancer, but wasn't sure of the price. It seems there are some pretty cheap/simple balance chargers out now. I'm really considering those 2 lipos for $30 now. It seems I wouldn't need much to get them running safely in my buggies or boats. Nice long run times is what I'm looking for with them.

Cheers,

Rob

I use the Maxpro alarm on my Traxxas Stampede. Works great and the alarm is quite loud for only $5 USD on Ebay. The alarm goes off when the voltage drops to 6.6 volts. This translates into about a 100 mah cushion before the battery is completely drained and approaching over discharge. It comes with about 8 inch wires and a jst-xh connector not soldered yet. Installation can be either wired to the main power wires or into the balancing pigtail on the lipo pack. I did the later with a switch in line so I can turn off the loud alarm without having to take the body off.

Mark is right that there is not a very noticeable falloff in lipo as it reaches 6 volts. I ran my lipo down in my DF03 with LVC until it stopped and then put the pack in my Stampede very briefly to get a feel for the dead pack. Still pulled a wheelie and was quite quick, so with lipo you can not safely judge voltage by speed/power falloff.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this