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View Full Version : I need sum book learnin !!



bbking9
03-31-2006, 05:13 AM
What causes the heat build-up with BL motors/ESC? (I know improper gearing can - so no need to discuss that point).

Is it because the batteries (example 8 cell NIHM) can't deliver the current/amps needed?

Is it because the ESC can't deliver the current/amps needed?

Is a 7.4V Lipo better than a 8 cell 9.6V NIMH? Why?

How do you go about matching a BL motor with a BL ESC.

Help me understand - my folks didn't go in for all that book learning when i was a kid.

leapingbug
04-01-2006, 05:20 AM
well first the heat issue: any resistance to an electical feild produces heat (+ resistance = Heat)

a 7.4v lipo is way better then any 9.6v nimh:Because first off a 7.4 lipo fully charged is actually charged at aprox8.2-9.1 (from my experence) and stays there longer then what a nimh would.A good way to think of this is as a road your driving a lipo and your going (longer i might add) down hill but can hardly notice then out of the blue whoo with out warning you drop off a cliff.

Now your driving a nimh and you start out flat for maybe a min then all of asuden you careining down as the road gets dramticly declined and you can see the bottom coming fast

(1800MH lipo =30-40 min 1800MH nimh=10-20 tops)

And for matching BL motors with ESC:
you hafta get a BL that is unfer the ESCs amp rating
(Example a mamba 25 esc can handle a BL motor with up to 25 amps a key figure is to get the to numbers as close as possible with out goin over the esc amp rating) :D

I know its alot to read but ya had alot ta ask lol :p

bbking9
04-01-2006, 03:25 PM
thanks leaping bug.

my 9.6 8 cell nimh's charge at 12.4V.

On matching the ESC to the BL motor. You say get a motor that is under the ESC. Do you mean continuous or peak usage - or both?

lipos vs nimh - do bl motors need amps or volts? my nimh p[ut out plenty of vlots - but not sure how many amps they put out compared to lipo.

good reply to my questions.

auto2
04-01-2006, 06:34 PM
in a 5 minute race a 9.6 volt will beat a 7 volt any day. much more punch with the extra voltage. Just get a 3 cell lipo at 11 volts and dont look back LOL!

mat3833
04-01-2006, 10:01 PM
ok the heat issue i can help out on. ok brushless motors come in 2 types sensored and sensorless. im going to talk sensorless here. the esc is fed voltage and current from the batts. the esc then sends those to the motor. when it reaches the motor it electrifies a coil of wire which creates a magnetic feild and lets the ESC kno its time to change the charge to another coil of wire. now this happens loads of times a second at high RPM. every time these coils get electrafied the resistance in them makes heat which is transfered to the can and cooled due to convection. now 2 main things can happen to make it heat up 1. the can doesnt get airflow and gets hoter which causes cogging and cogging causes more heat which causes more cogging, so on and soforth. 2. the can gets airflow but the motor is running at such a high rpm or under a great enough load that the heat generated by the coils gets greater due to the fact that more current is needed to generate the same magnetic feild to register on the ESC.
to solve both these problems reduce voltage or gearing. feel free to ask more questions or correct me if im wrong.

Matt

bbking9
04-02-2006, 03:00 AM
thanks matt. makes sense.

leapingbug
04-02-2006, 06:07 AM
thanks leaping bug.

my 9.6 8 cell nimh's charge at 12.4V.

On matching the ESC to the BL motor. You say get a motor that is under the ESC. Do you mean continuous or peak usage - or both?

lipos vs nimh - do bl motors need amps or volts? my nimh p[ut out plenty of vlots - but not sure how many amps they put out compared to lipo.

good reply to my questions.
On ESC matching w/ BL:well there are continuous and peak to both get em as close as possible.
And volts and amps: think of volts as you running, throw in the amps and now your running in water (resistance) increase the amps and you decrease the amount of water your running in thus increasing your efficencey (spelling :confused: ) more amps the more efficent the volts
And for amp rateing on lipos: try to get continous amps on the lipo higher then the peak of your ESC brushless combos amp :D ;)

mat3833
04-03-2006, 04:13 PM
no problem im glad i wasnt to confusing

Matt

FHM101
04-24-2006, 05:34 AM
Here's one for you electrical guys. I switched from IB1200 cells to 650KAN cells and aside from losing 49 grams, my buggy seems much more peppy than it did with the 1200's. I get a lot more punch and low end and actually have some head room to play with, and motor temps are never over 160F. I did drop from 20 or so minutes of runtime down to around 8 minutes, but other than that it's been an across the board improvement to run the 650 rather than 1200 cells. Is the improvement just from less battery weight? Oh, I'm running a mamba 25 control and a hyperion 5000 with a 12T pinion.

BiGRoB21
04-24-2006, 02:34 PM
the kan 650 cells are nicads. and nicads normally have a more punchy feeling. and making the car lighter will put less strain on the motor to move which will lower the motors heat

afonsos
04-24-2006, 03:51 PM
the kan 650 cells are nicads. and nicads normally have a more punchy feeling. and making the car lighter will put less strain on the motor to move which will lower the motors heat

Are you sure that kan650s are NiCd I have some cells from an aircraft and they are printed as nimh. :confused:

nicd or nimh Kans are great cells.

BiGRoB21
04-24-2006, 04:17 PM
im petty shure that the 1st nimh ones from kans were the 950's and the 650's were nicd's

afonsos
04-24-2006, 04:50 PM
Are we talking about same cell? :D

kan650 (http://www.cheapbatterypacks.com/cellinfo.asp?invid=KAN650)

FHM101
04-24-2006, 05:45 PM
I just checked my cells and they are stamped ni-mh.

bermbuster
04-24-2006, 06:54 PM
kan cells are nimh.... a kr is the nicad version. a kan 6502/3aa cell weighs roughly 1/2 oz. while ib 1200s weigh 3/4oz.
At what amperage did you charge the 650s??? Maybe your 1200s have seen better days......

BiGRoB21
04-24-2006, 08:12 PM
i stand corrected.

FHM101
04-25-2006, 06:23 AM
At what amperage did you charge the 650s??? Maybe your 1200s have seen better days......

I charged both at .50 amp with the lowest dropback available on my pitbull (.012). Could be the 1200's just need more cycling as I only charged and ran them a few times before I switched to the 650's. My knowledge of nimh cells is limited to these, as I got out of 1/10th electric racing when 2400 nicad cells were the hot ticket so I never used nimh for anything but a nitro receiver pack before I started with the half 8. For all you nimh veterans out there, what is the best way to treat these cells?