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jeeves_m_d
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PostSubject: Overvolting   Fri Dec 18, 2009 11:37 pm

So when it comes to electronics i know my basics, but my knowledge is very limited. When it comes to overvolting, how far can i take it? I understand that i cant go past the limits of the speed controller, but I dont seem to have to worry about that with the scorpions being rated to 28V what I'm worried about is the RS-550 motor from banebots, RJW mentioned that the rattlers use the motors at about 18V. Eventhogh banebots website say they are rated for 14.4V.
So my questions is how high a voltage will i be able to apply to the RS-550 motors? how woud i calculate this, and if its too hard to explain could you just tell me is 21-24V would be too high?
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PostSubject: Re: Overvolting   Fri Dec 18, 2009 11:52 pm

It's amperage that will kill both the 550's and the Scorpions...ask me how I know

Don't do this:

We were bench testing some very serious 550 motors with a Scorpion XXL ....bot standing on back end with wheels in the air....and a 6 cel lipo pack!!!

After some wonderful results and incredible speed and torque, this iswhat happened...

Full throttle forward....then pulled back to ful throttle reverse...

Poof.... affraid the Scorpion went up in a cloud of smoke...litke a mini atom bomb... bounce

Chris from robot power said that it was the voltage/amperage rush that killed it....the esc can see spikes higher than actual battery voltage.

Down to 5 cel, everything was ok...brushes wore out prematurely.

With A 123's 5 cel no problem...6 cel touch and go but doable if your drive accordingly

With lipos, 4 cel no problem...5-6 cel...you're on your own....just don't do the no load fwd/rev test, unless you video it and share... cheers

Remember that a 5 cel a123 charges to 18v, but a little load and your in the 16's

Lipos and LiIons are different in how they drop voltage over time...do some research

remember this is just our expereince and therefore jmo

Edit: keeping things cool = more voltage/amperage capability

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Cody
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PostSubject: Re: Overvolting   Sat Dec 19, 2009 1:11 am

i wouldnt recomend running much over fourteen volts to your 550s honestly, all depending on the specs of the motor of course.
The brushless motors we use are much beter suited for high amperage/voltage of course as to say the BB's
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PostSubject: Re: Overvolting   Sat Dec 19, 2009 1:28 am

Cody Harris wrote:
i wouldnt recomend running much over fourteen volts to your 550s honestly, all depending on the specs of the motor of course.
The brushless motors we use are much beter suited for high amperage/voltage of course as to say the BB's

Are you guys running brushless drive motors now?

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PostSubject: Re: Overvolting   Sat Dec 19, 2009 9:25 am

Run a Dual Voltage out of the batteries and send 13.2 to the drive motors and 19.8 to the weapon motor!

Works pretty good if you can work with the added weight!
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PostSubject: Re: Overvolting   Sat Dec 19, 2009 9:58 am

I might just end up doing the dual voltage, it seems to be the easiest solution. I had tried this before with the NiHM batteries i had and they just couldn't take it, but the a123's do seem to have a high enough discharge rating
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PostSubject: Re: Overvolting   Sat Dec 19, 2009 11:42 am

i worded that wierd lol but no i just ment the weapon motors can handle it better, of course there also rated for it so its kinda a given haha
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PostSubject: Re: Overvolting   Sat Dec 19, 2009 12:15 pm

How exactly do you run a dual voltage out of lets say, 6 A123s, and i want 4 to go to driving, and the whole 6 to the weapon...
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PostSubject: Re: Overvolting   Sat Dec 19, 2009 1:36 pm

Josh Raichel wrote:
How exactly do you run a dual voltage out of lets say, 6 A123s, and i want 4 to go to driving, and the whole 6 to the weapon...

Simple....just install a red wire to the positive end of the 4th battery and anothe black wire to the ground end of the pack

Voltage between those 2 wires will be 4 cel..... or around 14v.....voltage at original wies will still be 6 cel

We do this with ours, but on the A123's we have a polycarb housing that we made, so none of the cels are soldered and NO tabs...we can also check voltage at each cel and replace any that are weak.

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PostSubject: Re: Overvolting   Sat Dec 19, 2009 11:31 pm

Yeah, you gotta check out what Team Jag does with their homemade A123/NiMh battery packs--it's so obvious when you see it, it's a wonder more hobbists and bot builders haven't done it before. It sure as heck beats trying to solder directly to batteries--and having to replace a whole pack when only one cell dies.

The dual voltage thing scares me a bit with the LiPos, just because every manufacturer makes such a deal about balancing the cells, it seems foolish to discharge part of a pack more than another part, but Will Bales has done this very successfully for nearly a year now, so I'm convinced. . .

. . .Well, his robot DID catch fire. . .hmmm.

We never really asked ourselves if split voltage was a contributing factor--we just assumed that the stalled 4-horse motor and 180 amp speed controller were the problem and that the battery burnt after the ESC shorted. I know that in the video the fire seems to begin in the drum, where the motor and speed controller reside, but maybe that's just because we couldn't see into the battery compartment.

As for overvolting--I agree with all of the above, with this addition--if it's the amps that kill the motor, then high quality, modern LiPos are more tricky than any other battery. When a battery has such low internal resistance, it can maintain a much higher voltage for the current drawn. This means the brushes, commutators, and windings all have to be lots tougher to handle a stall (or worse yet a full reversal).

If you have the $$, I wouldn't recommend using the BB 550's--buy high quality 550's from Tower Hobbies or someplace similar. Ideally, you will have time and money to buy several and compare their brushes, but always check their specs!!
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PostSubject: Re: Overvolting   Sat Dec 19, 2009 11:38 pm

Off topic for a moment

In one angle of the video, you can see some sparks or fire in the drum...before it goes up in flames. This seems to occur at a moment when ttatt was pushing fluffy from behind, then it seemed like either fluffy was caught in a floor seem or fluffy's drum operator was trying to spin the drum, which was helping fluffy to resist the push.

If that was the case, then I'm sure that every bit of amperage that the batteries and esc could supply was going into the motor, which might have caused something to overload and catch fire.

Sorry for the hijack

Back on topic....

The bb550's have worked well for us on up to 5 cel A123's.. I wouldn't run them full tilt on a 5 cel lipo and expect them to live very long.

We've had good success so far, using lipos and tapping lower voltages, but only with castle esc's. You can program them to shut off the weapon when cel voltage gets too low. In the case of Thunder Power lipos, I believe they recommend no lower than 3.3v per cel. A spinning weapon will probably bring down the pack faster than the drive esc, so once the weapon shuts off, you know that you're close.

A balancing charge will bring all cels back up , unless one is damage..but balancing while charging takes a lot more time than just charging.

With Lipos, best to have at least 3 packs. With A123's 2 is enough...or even 1 if you don't mind quick charging them.....

again jmo from our experience.

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PostSubject: Re: Overvolting   Sun Dec 20, 2009 10:26 am

Sorry if i sound a little stupid here but i always just plug my battery packs into the triton charger and wait for it to tell me its charged, i assumed that all the cells in the pack were charged equally, what is this balancing stuff you talking about?
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PostSubject: Re: Overvolting   Sun Dec 20, 2009 1:03 pm

you can draw more power from different cells then others basically
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PostSubject: Re: Overvolting   Sun Dec 20, 2009 1:08 pm

Ok so that means the cells are unbalanced, how would you go about ReBalancing them"?
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PostSubject: Re: Overvolting   Sun Dec 20, 2009 2:24 pm

google
http://www.dream-models.com/eco/electrics-charging.html
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PostSubject: Re: Overvolting   Mon Dec 21, 2009 8:54 pm

Ok so We have decided to buy the new a123 cells, I ussually get batteries from robot marketplace, but i was wondering if anyone new any alternative places to get them?
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PostSubject: Re: Overvolting   Mon Dec 21, 2009 10:08 pm

jeeves_m_d wrote:
Ok so We have decided to buy the new a123 cells, I ussually get batteries from robot marketplace, but i was wondering if anyone new any alternative places to get them?

battlepack.com is the last place we bought some from, but it looks like they want you to either email them or go to rmp

.....I've heard ebay??? where's Cody when you need him?

peakbattery.com imports the k2 batteries...same size as A123, but not quite as god $13 per cel..also a bit heavier

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PostSubject: Re: Overvolting   Tue Dec 22, 2009 12:42 am

we bought a couple dewalt packs off ebay before, I dont remember where alex got the newest ones from.
If you go to the gen discusion thread and will new favorite site i believe they had them listed as well as many other hobby sites do
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