NiMH & NiCAD in parallel ?  
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All Forums >> Radios, Batteries, Clubhouse and more >> Batteries & Chargers >> NiMH & NiCAD in parallel ?
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NiMH & NiCAD in parallel ? - 5/16/2002 6:26:01 AM   
SkyChi


 

Posts: 7
Joined: 1/19/2002
From: Memphis, TN, USA
Status: offline 		When using a dual switch and battery system can you mix NiMH & NiCad batteries as long as they are the same voltage ?

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Mark
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NiMH & NiCAD in parallel ? - 5/16/2002 6:19:50 PM   
LJE4357


 

Posts: 40
Joined: 4/17/2002
From: Orlando, FL, USA
Status: offline 		You cannot parallel NiMH or NiCad batteries unless you diode isolate them, then you will have to add another cell to make up for the diode drop.

Larry Epifanio
SouthEast Model Products
R/C World, Orlando, Fl.

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NiMH & NiCAD in parallel ? - 5/16/2002 6:24:33 PM   
Forgues Research



Posts: 3414
Joined: 12/15/2001
From: Glen Robertson, ON, CANADA
Status: offline 		[QUOTE]Originally posted by LJE4357
You cannot parallel NiMH or NiCad batteries unless you diode isolate them, then you will have to add another cell to make up for the diode drop.

Larry Epifanio
SouthEast Model Products
R/C World, Orlando, Fl. [/QUOTE]

The diode drop is only .6 volt

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NiMH & NiCAD in parallel ? - 5/17/2002 4:52:27 AM   
LJE4357


 

Posts: 40
Joined: 4/17/2002
From: Orlando, FL, USA
Status: offline 		actually its only .6 volts if its germanium, and .7 volts if its silicon, and since most diodes are silicon......well. Also the drop increases with tempurature rise. So a good rile of thumb is about a volt. Using an extra cell give a little extra overhead. If you want to parallel batteries, use Lithium , and this is a whole nother story.

Larry E.

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       Post #: 4

NiMH & NiCAD in parallel ? - 5/17/2002 5:26:44 AM   
k7dfw



Posts: 95
Joined: 4/3/2002
From: CLATSKANIE, OR, USA
Status: offline 		There is some inaccurate info being dished out here.

The following is from one of many sources and describes what is accepted as the voltage across a PN junction.

.........................................................................................

"What is the meaning of Vf as it relates to a diode or rectifier?

Vf is the forward voltage drop of a semiconductor. It consists of two components; an intrinsic offset voltage (0.3 volt for germanium ; 0 .7 for silicon) plus If x R, where R is the resistance of the semiconductor and leads multiplied by the current, If. Vf is undesireable and is minimized whenever possible as it adversely affects the efficiency of the circuit and results in a power loss, that loss is Vf xIf."


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NiMH & NiCAD in parallel ? - 5/17/2002 5:38:51 AM   
Jazzy



Posts: 1106
Joined: 1/8/2002
From: Erie, PA, USA
Status: offline 		Just curious. Why must they be isolated when they are connected to the reciever via different chanels? What would happen if you didn't isolate then from eachother?

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NiMH & NiCAD in parallel ? - 5/17/2002 7:38:40 AM   
Ed


 

Posts: 1812
Joined: 12/5/2001
From: Bemis, , USA
Status: offline 		[QUOTE]Originally posted by Jazzy
Just curious. Why must they be isolated when they are connected to the reciever via different chanels? [/QUOTE]

There is no isolation between channels, the positive and negative voltage bus is common across the entire receiver. Only the signal lines are isolated, or different for each channel.

GeeBeeJim

< Message edited by GeeBeeJim-RCU -- May 17 2002 4:39PM >

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       Post #: 7

NiMH & NiCAD in parallel ? - 5/18/2002 7:25:22 AM   
hebertjj


 

Posts: 323
Joined: 1/18/2002
From: Knoxville, TN, USA
Status: offline 		I agree with K7, I think someone here needs to change his username to "Cliff Claven".

When's the last time anyone even SAW a germanium diode?

Instead of lithium, I'd like to recommend a "whole nother story":
Fuel Cells; in parallel; WITH GERMANIUM DIODES !!!

Why can't you hook a nicad and nimh pack in parallel? If one pack has a cell go bad, it's going to put a slight load on the other pack, but the other pack ought to hold the voltage up to a level sufficient to make it back home. I don't know if I'm going to do it, but what's the worst that could happen? (I know, a flaming plane; into the parking lot; hitting your car; with your new plane in it.)

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NiMH & NiCAD in parallel ? - 5/18/2002 6:54:10 PM   
Vince


 

Posts: 1650
Joined: 2/2/2002
From: Nederland, Tx.
Status: offline 		[QUOTE]Originally posted by LJE4357
You cannot parallel NiMH or NiCad batteries unless you diode isolate them, then you will have to add another cell to make up for the diode drop.

Larry Epifanio
SouthEast Model Products
R/C World, Orlando, Fl. [/QUOTE]

Sounds as thought it's time for a visit to Red"s battery clinic. Take a look at the page on "Parallel Operation = Reliability & More Flight Time".

http://www.rcbatteryclinic.com/

Vince

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NiMH & NiCAD in parallel ? - 5/18/2002 8:19:30 PM   
Jazzy



Posts: 1106
Joined: 1/8/2002
From: Erie, PA, USA
Status: offline 		Jim,
I realize the buses are common across the board. But why shouldn't one do it? Separate switches & charging jacks...
Other than having to, (maybe), charge the two packs differently, what is the big deal?
Me, personally, I wouldn't do it with a large, expensive, plane. I'd match the packs for simplicity sake.

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Re: NiMH & NiCAD in parallel ? - 5/18/2002 11:33:51 PM   
Ed


 

Posts: 1812
Joined: 12/5/2001
From: Bemis, , USA
Status: offline 		[QUOTE]Originally posted by SkyChi
When using a dual switch and battery system can you mix NiMH & NiCad batteries as long as they are the same voltage ? [/QUOTE]

Jazzy: I like your idea best - "Me, personally, I wouldn't do it with a large, expensive, plane. I'd match the packs for simplicity sake."

Why SkyChi wants to mix the two different battery chemistries, I'll never know. I'm gonna have to guess that their internal resistance is gonna be different, and that might be problem enough ......... Just go out and buy a matching pack.

I'm sure that Red is going to jump in here in a minute, and set us straight on the difference in battery chemistries, and internal resistance. At least, I hope he does.

Jim

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NiMH & NiCAD in parallel ? - 5/19/2002 1:27:53 AM   
SkyChi


 

Posts: 7
Joined: 1/19/2002
From: Memphis, TN, USA
Status: offline 		Jim,
The reason I considered mixing the two was just pure convenience. I've just bought my first NiMH packs but have a few good but smaller NiCADs around. While I don't think I've read any definitive reason not to mix the two I don't think I will. That whole "Burning plane crashing in the parking lot" thing kind of painted an ugly picture for me. Thank You all for your input.

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Mark

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Hey Guys - 5/19/2002 4:23:23 AM   
zero244


 

Posts: 176
Joined: 1/19/2002
From: Mcminnville, OR, USA
Status: offline 		Sounds like a good idea to me. I dont know if you should do it. But think about it............you have one 600 nicad pack and another 1600 mah nmhl pack that is equal in size and weight to the 600 mah nicad pack. Would you rather have 600 mah in backup power or 1600 mah in backup power.

Yes Red jump in here..............we need the final word to ease our minds one way or the other.


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Re: Hey Guys - 5/19/2002 4:59:10 AM   
Forgues Research



Posts: 3414
Joined: 12/15/2001
From: Glen Robertson, ON, CANADA
Status: offline 		[QUOTE]Originally posted by zero244
Sounds like a good idea to me. I dont know if you should do it. But think about it............you have one 600 nicad pack and another 1600 mah nmhl pack that is equal in size and weight to the 600 mah nicad pack. Would you rather have 600 mah in backup power or 1600 mah in backup power.

Yes Red jump in here..............we need the final word to ease our minds one way or the other. [/QUOTE]

Why not simply get another NmHd pack, they are not that expensive, and your airplane is worth it.

http://www.aerografixs.com

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