monkey wrench

hi,

new here.

i decided to get an mmp/2400kv sct combo for my slash 4x4. i have a 3s 20c venum bat. and 2s 20 bat. they are both fairly new. will using these bats in the mmp/2400 combo cause any issues? other than than lower speeds. will the increased demand for amps cause the bats to overheat?

i'm new to the hobby and still getting my head around all the electronics info.

thanks.

SyCo_VeNoM

Depending on the capacity chances are it will trash the batteries by over taxing them

Calculation to figure out the max current a battery can output is C-rating X (capacity in mah)/1000 like for example your battery is 20C and the capacity is 5000mah it would be 20X(5000/1000) which would equal 100Amps of current can be pulled

monkey wrench

i guess ill need to upgrade my bats.

savagecommander

youll get by on the 20C batts. just dont go crazy with the gearing. i ran 20C 4s batts with my 2400 and had no problems. just be sure to set your lvc to 3.5-3.7 and youll have good battery life.

phmaximus

Are they the venom 3s 5400mah ones? They are only good for 108a

I wonldent reccomend running them at all, they would just be ok for a 2wd slash with SCR wheels but not 4x4 slash.
My 2wd slash pulls 70a... tested with watt meter, And can only guess but I would say a 4wd pulls over 110a easily

Foxy

20C will be fine for 2400kv, even the 4 poles. If it was a 5400kv or something, that would be a different story, but that motor won't pull even close to 100A continuous in any car unless the wheels are stuck. The Mamba Max Pro itself is only rated for 64A continuous.

Gear conservatively and watch for heat/swelling. I'd be more concerned that the C rating of most batteries, even the expensive ones, isn't actually what it says on the sticker. Often, they are 20% or more, less than stated. If the batteries are coming off the car hot, (and I mean hot, not just warm), then discontinue using them. Setting the cutoff high will also not provide any benefit, leave it at 3.2.

monkey wrench

thanks for the info. i had no idea what that motor would draw amps wise. and i had the same thought regarding c ratings and whether or not they are accurate. i'll keep an eye on the bat temps. if the 2s works out it would be nice since the only track close to my house limmits bats to 2s. i dont plan on racing very often but knowing the motor esc combo can work with 2s bats is nice.

phmaximus

Ur tripping. "20c" is just a multiplier its not the output current. U can't just say its going to be fine. There is no mention of what MAH rating the battery has for all we know it could be the Venom 20c 3s lipo 2100mah.

I strongly disagree, yeah sure some 20c batteries will be ok but the majority won't. I would never recommend a battery with out knowing its specs. If the OP is running the 2100mah u have basically told him its going to be fine and should work on a 4poll..... That couldn't be futher from the truth. I wouldn't even run that battery on a 380 cored motor..... Its only 42a with no specs for max current....

lets say the OP has a hobby wing 35a ESC, they pull up to 190a burst and 35 continuous.... 99% of 20c batteries are not even up to the specs of that. I've proven with a 380 core single poll motor can pull 70a with loss of traction. High traction bite it would pull more. 80a???

So its safe to say a 540 motor with a 60a ESC is going to pull alot more in a 4x4 slash than my 2wd slash did with a 380
My bet on burst its going to be pulling over the max current draw for 99% of the 20c batteries. Generally the batteries absolute max burst rating is not much higher than continuos rating.
If u are bashing this is going to be a massive problem....

We can guess and argue all day about this, but I Say... Amp meters are cheap. Do u own test if u don't believe me.

well hope that helps, good luck

SyCo_VeNoM

Agree
Also its a slash 4X4... that sucker is going to be pulling the max.

monkey wrench

dang. heated debate!

both of my 2s bats are 5000mah.

appearantly i need to educate myself. i thought the mah ratings were related to run time but now it sounds like they have some relation to max amp output as well.

i do own a multimeter so ill see what i get once i get the combo installed.

phmaximus

Nar m8 not heated at all, it's just everyone does things different. I've got great respect for foxy...

to Wouk out the max current output, devide the mah rating by 1000 then times it by the c rating. That will give u the output in amps...

heads up most multimeters are limited to only 10a... But 200a gauges with a bridge are cheap

phmaximus

So ur batteries... Are 5000mha 20c 3s

thats 5000mha / 1000 x 20 = 100amps.... Not much room for a 540 motor with 4 wheel drive... I think those batteries are more suited to 1/10 touring cars and smaller 380 size motors on micro/mini offroaders and small 1/10 2wd offroaders..

Foxy

If they are 5000mah or more they are fine I'm telling you. Like I said, the MMP is only rated for 64a continuous. Don't confuse burst with continuous delivery. A Savage Flux with a 1/8th 42mm 2350kv motor does not even pull 80a continuous. It has a good burst of probably around 150, but not continuous.

Look I'm not saying these are the ideal batteries for the application, more current is always preferable, but I do not believe anything is going to be harmed by using them, except perhaps slightly reduced battery longevity.

Of course as I said above and as syco echoed, this is all aiming they are genuine 5000mAh @20c.

SyCo_VeNoM

Well if they are 5000 they more then likely would be ok, but they are venom batteries so I dunno about that as their NiMh were no where near printed ratings.
If they changed their lying on the label then yea, but I can only go based on the old NiMh's I owned from them that would take 1400mah less then then the sticker had listed from dead.

phmaximus

Venom don't list a rating for burst current so I would treat the c rating as max current including burst.
When u look at similar batteries with 20c the burst rating is still only 30c.... Sure high quality cells can burst up to twice its c rating but I don't think these can. Even with a max burst of 120a with 30c its still to close for my liking.

its to close to call, but if that slash was to pull over 120a on a hard launch on a high traction surface there will be issues.

I would hate to se the car run great for the first 1/2 of the pack, then during a hard launch it suffers from excessive voltage drop and resets the receiver.... That could be an excess of 3 seconds with absolute no control of the car while its moving.... I've had this with a external BEC cutting out before the LVD... Lets just say its no fun

my advice to the OP try it, but get some new batteries ASAP, as no doubt u will see a performance increase because the cells won't be working as hard and won't loose as much voltage under load, where ur current cells will be working a 100% when taking off.

allso if u notice that the motor under full throttle launches is hesitating, lower ur gearing and back of the slipper so it slips for the first few feet. That will lower the current draw

The Shop

Those batteries won't cut it on a Slash 4X4, that thing is heavy and draws a lot. Play it safe and get a high quality 30C or so, no reason not to and gamble.

phmaximus

Don't know if its true, but I was reading... There is a change of damaging the ESC if the supply if lower than the draw.... And defiantly the batteries

I wonder how the ESC could get damaged?

Foxy

Its called 'ripple' the thing that damages escs but I won't pretend I understand how it happens or why. Like most of the physics of electricity, it's probably quite simple once you read an explanation, I just never have.

No 1/10th is ever going to pull more than 100a, thats just crazy. What makes you guys think the current requirements are so high? Im gonna make a long post one of these days *****ing about how the manufacturers have inflated all the requirements of RC cars across the board, from servo torque to amp draw to batteries to escs, everything. Its just so you'll feel your old stuff isnt good enough and buy the latest amd greatest, but yeh, thats a subject for anothrr thrwad when im not typing on my phone.

phmaximus

hummmmm I beg to differ.... under burst, things go crazy.... check out this video I made?

It shows a slash with stock crappy wheels with conservative gearing 23/87 on only 2s... as u can see it peeks at 73amps
and also that's under total loss of traction.

on a full throttle launch with the current wheels (JC subcultures) on carpet its enough to wheelie about 20mm high... Im yet to confirm but I bet its pulling over 73a on take off....
I dare say my current setup but with stampede wheels and decent traction it could very well pull over 100a... or current wheels and taller gearing might too

http://www.youtube.com/watch?v=xbQcM_qJ5C4
I do agree that there is a great exaggeration with most rc cars and how much continuous current they draw,

phmaximus

ive got some interesting thoughts on the effects of the brakes and punch setting of a vehicle with a over kill ESC... I think it will limit the effective tuning range of those settings.

savagecommander

well?

Foxy

I think your video shows I'm right. That motor cannot pull more than 7xA, or it would have during the load test (assuming your batteries and ESC are capable). That is also a smaller (in mechanical terms) less efficient motor, as well as higher in kv. The castle will be able to do much more with the same amperage supplied. I maintain that a 2400kv 1415 cannot pull 100A in a 1/10th short course, except for a split second.

But wait, in order not to digress from the thread, we are now at least in agreement, that 100A is going to be the absolute max burst that the OP is likely to experience. Therefore, his 5000mAh 20C batteries (assuming they are rated accurately) can nominally maintain indefinitely, the kind of amperage that the motor will only ever draw for split seconds. This covers my personal golden rule of lipo, that your battery's nominal C rating should equal or exceed the maximum burst that the system can draw. This is why I get 5000@40C for the 1/8th stuff, never gonna see over 200A.

But really, the bottom line again is whether or not the cells really are going to do what they say they can do. Many people have problems with low rated packs in the 4x4 slash, but as we can all see in PH's video, it's not because of excess strain on the equipment, that 70A figure doesn't go up a lot for a 4wd, a bit sure, but it doesn't even go up that much in a 1/8th buggy with a 42mm motor either, also typically bursting at around 100A.

So what does the OP take away from this...even if he said to himself, I need to upgrade my batteries, what's he gonna do with the old ones, burn them for fun and profit? Might as well use them, run them into the dirt, they'll probably only do half as many cycles as they should, and they'll swell a bit, but don't worry about it, use the time to save up for some Nanotech A-specs, or the new Gens Ace quality one they just came out with...

monkey wrench

thanks again for all the info. shopping for lipos when there is no c rating standard is difficult.

if a manufacturer lists their battery's burst and continuous current in amps, do you feel that's a reliable number? or are the methods for measuring, whether in c's or amps, non-standard?

as you mentioned foxy, i'll likely run the lipos i have have untill they are toast. could be 5 cycles could be 100. unless I can sell them to a friend looking for a couple 2s bats at a discount.

monkey wrench

also, i forgot my tqi controler has the ability to measure amps. i'll see if i can set the alarm for say 80 amps. if i can figure out a way to measure the bat's max output in amps i'll be good.

Foxy

There is a standard (the formula as mentioned is mAh*C) it's just that they lie. It is getting better though. Funnily enough, it seems the most reliable c ratings are found on the cheaper Chinese packs. I use a lot of zippy packs, which I am confident are accurately rated. They give a nominal and a burst rating.

Don't worry about measuring your amperage, is not like you can do much about it anyway... Run them till they die then get something better.