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Old Feb 28, 2003, 08:55 PM
Registered User
Antioch CA
Joined May 2002
95 Posts
Will this fry my brushless controller?

Controller is a Jeti JES 70-3P with BEC 7 to 12 cells

Can this controller handle more that 12 NiCads? And still provide BEC?

Can I use this with a 13 cell 3000NiMH?
My logic is; since voltage from NiMH is 1.1 Vs. Nicads at 1.2 then a 13cell NiMH has slightly lower voltage than a 12cell Nicad. Is this correct?

Thanks in advance for your help
Dennis
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Old Feb 28, 2003, 09:02 PM
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sneu's Avatar
United States, CA, San Diego
Joined Dec 1999
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Wrong! Nicads and NIMH have the same voltage. In any event the problem is overheating the BEC. If that happens it will stop supplying the 5 volts needed for the radio. Be safe and use a small Rx battery.

Steve
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Old Feb 28, 2003, 09:13 PM
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rc-eflyer's Avatar
St. Louis, Missouri, United States
Joined May 2002
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Quote:
Originally posted by sneu
Wrong! Nicads and NIMH have the same voltage. In any event the problem is overheating the BEC. If that happens it will stop supplying the 5 volts needed for the radio. Be safe and use a small Rx battery.

Steve
Wrong! Control Freak is correct, NiMhs have a lower nominal
voltage per cell as a general rule. Steve is right though about
overheating the BEC as it has to drop more voltage to get
down to the 5V which is dissipated as heat.
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Old Feb 28, 2003, 09:38 PM
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William A's Avatar
Tacoma,WA USA
Joined Jun 2001
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Re: Will this fry my brushless controller?

Quote:
Originally posted by ControlFreak
13 cell 3000NiMH
If your going to fly a plane that can handle that much weight, I'd go with a 4-5 cell flight pack or a UBEC.

Your asking a lot from your speed controls BEC circuit for that many cells.
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Old Feb 28, 2003, 09:48 PM
Registered User
Antioch CA
Joined May 2002
95 Posts
Can I use a fight pack w controller w BEC

Can I use a fight pack with controller that has BEC?
And if so can how many cells? The controller says "6 - 12 NC" on the label.

Thank you
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Old Feb 28, 2003, 09:54 PM
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William A's Avatar
Tacoma,WA USA
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Re: Can I use a fight pack w controller w BEC

Quote:
Originally posted by ControlFreak
Can I use a fight pack with controller that has BEC?
Yes, just remove and isolate the power wire between ESC and Rx.
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Old Feb 28, 2003, 10:15 PM
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Jim McPherson's Avatar
Laurel, Maryland USA
Joined Aug 2000
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Quote:
Originally posted by rc-eflyer
Wrong! Control Freak is correct, NiMhs have a lower nominal
voltage per cell as a general rule. Steve is right though about
overheating the BEC as it has to drop more voltage to get
down to the 5V which is dissipated as heat.
Wrong! Nominal voltage of NIMH's is the same as NiCad's. NIMH's tend to sag in voltage a bit more than nicads during flight, this gives rise to the 1.1 volt philosophy. However, NIMH's are getting better and better and sag less now than ever. If your counting on sag so that you don't blow your ESC up, your walking on very thin ice. My advice: Get a UBEC or use an Rx battery.


-Jim
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Old Mar 02, 2003, 01:23 AM
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rc-eflyer's Avatar
St. Louis, Missouri, United States
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Quote:
Originally posted by Jim McPherson
Wrong! Nominal voltage of NIMH's is the same as NiCad's. NIMH's tend to sag in voltage a bit more than nicads during flight, this gives rise to the 1.1 volt philosophy. However, NIMH's are getting better and better and sag less now than ever. If your counting on sag so that you don't blow your ESC up, your walking on very thin ice. My advice: Get a UBEC or use an Rx battery.


-Jim
OK, "nominal" was a poor choice of words but I think
the common understanding and use of NiMh for our purposes
and what ControlFreak was referring to in the original post
was that we normally use a greater number of NiMhs than
NiCd to acheive the same voltage under operating conditions.
So just saying they have the "same" voltage was not a good
answer to the orignal post imho and that's why I considered
it "wrong". I do agree with your statement about the "thin ice".
I apologize if I stepped on any toes , I never meant to.
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Old Mar 02, 2003, 01:58 AM
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The high rate NIMH and Nicads have teh SAME voltage under load. In fact some of the latest NIMH actually have higher cell voltage that the same sized Nicads. The is no reason to add cells if you use quality batteries intended for high rate use.

Steve
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Old Mar 02, 2003, 03:48 AM
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rc-eflyer's Avatar
St. Louis, Missouri, United States
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Quote:
Originally posted by sneu
The high rate NIMH and Nicads have teh SAME voltage under load. In fact some of the latest NIMH actually have higher cell voltage that the same sized Nicads. The is no reason to add cells if you use quality batteries intended for high rate use.

Steve
That, I did not know . That's why I love this forum, you
can always learn something if you are willing to keep an
open mind. Thanks Steve.
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Old Mar 02, 2003, 12:13 PM
Registered User
Antioch CA
Joined May 2002
95 Posts
It did not fry

Nothing like real world flight test

Flew today on 13 cells. Put it through some serious paces and no fried speed control. My guess is that the manufacturers rate at level below what it can actually handle ... to provide a safety margin.

Tomorrow I try 15 cells (just kidding!)

Thanks for all the responses
Dennis
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Old Mar 02, 2003, 12:37 PM
Mmmm... crunchy balsa.
harryo's Avatar
United States, CA, Oakland
Joined Sep 2002
490 Posts
Dennis, You flyin today!?!

Be very very careful of your servo current draw. If there is asbolutely no binding or friction on them, then you might be okay. When flying at high speeds, you know these servos draw more current. So it becomes another gamble.

Added: As the vIN to the ESC increases, it has to work harder to provide the 4.8v to the receiver. This increases the risk of cooking the BEC FET.

How many servos? What kind of plane? Is it your hotliner?

Just asking 'cause I lost an ESC from this very thing. Luckily, it was on the test stand. The ESC was rated for 3 servos up to 10 cells, so I tried 12 cells. Wouldn't you know, I got record breaking thrust measurements. (for about 10 sec) Then I moved the control surfaces and everything whent dark.

When it comes to recievers and radio equipment, I'll never stray from the suggested parameters. Motors, ESC and batteries on the other hand...

So what's the deal? you flying today or what?!?

cheers,
-=h=-
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Last edited by harryo; Mar 02, 2003 at 01:24 PM.
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