Update - NiMH and NiCad in same plane....

Update - NiMH and NiCad in same plane....

Post by Jim Whi » Fri, 18 Jun 1999 04:00:00



As an update on my battery experiment, I tried this:

I charged all four packs overnite (14 hours) at the 1/10 C rate.... 80
ma for the two 800 mah NiCad packs, 210 ma for the two 2100 NiMH
packs....

( remember, the initial,post 3 cycle, discharge time for the packs was
2:14 for the NiMH at 1/2 C, and 2:10 for the NiCads at 1/2 C )

I took packs #1, one each NiCad and NiMH, and installed them in the
plane and flew 4 flights.  I took the #2 packs along in the tool
box....

I got home and left everything in the garage for 10 days, got to over
95 deg during the afternoons...

I discharged remaining capacity and found this:

NiMH:
        #1 1:59:28 (flown)
        #2 2:00:05
NiCad:
        #1 1:48:21 (flown)
        #2 1:44:40

hmmmmm..... what to observe... well, first off, contrary to what I've
heard, it appears that the self discharge of the NiCad's is higher
than the NiMH's....  and after 10 days of sitting and self discharging
in moderately hot environment, the effects of 4 flights on relatively
high capacity batteries is apparently masked out or equalised or
whatever by the self discharge....  ????   anyone ???

and yes, I'm absolutely sure I didn't get the two NiCad packs mixed
up....  and the initial discharge times on these packs was within 30
seconds of each other...

I guess the only meaningfull info here is that the NiCads have a
higher self discharge rate....

Jim White
AMA 2466
WB2WOY
WPMPA/BCF/PFC
SouthShoreSoftware
Treasure Island, FL

 
 
 

Update - NiMH and NiCad in same plane....

Post by Cregge » Fri, 18 Jun 1999 04:00:00


I had always assumed that the NiMH batteries had a higher cell impedance,
thus the warnings about attempting to rapid charge them. It would appear
that the self discharge rate is also affected by the higher impedance? I'm
just poking around here and do not claim to know diddly about either type of
batteries.

Ed Cregger


Quote:

> As an update on my battery experiment, I tried this:

> I charged all four packs overnite (14 hours) at the 1/10 C rate.... 80
> ma for the two 800 mah NiCad packs, 210 ma for the two 2100 NiMH
> packs....

> ( remember, the initial,post 3 cycle, discharge time for the packs was
> 2:14 for the NiMH at 1/2 C, and 2:10 for the NiCads at 1/2 C )

> I took packs #1, one each NiCad and NiMH, and installed them in the
> plane and flew 4 flights.  I took the #2 packs along in the tool
> box....

> I got home and left everything in the garage for 10 days, got to over
> 95 deg during the afternoons...

> I discharged remaining capacity and found this:

> NiMH:
> #1 1:59:28 (flown)
> #2 2:00:05
> NiCad:
> #1 1:48:21 (flown)
> #2 1:44:40

> hmmmmm..... what to observe... well, first off, contrary to what I've
> heard, it appears that the self discharge of the NiCad's is higher
> than the NiMH's....  and after 10 days of sitting and self discharging
> in moderately hot environment, the effects of 4 flights on relatively
> high capacity batteries is apparently masked out or equalised or
> whatever by the self discharge....  ????   anyone ???

> and yes, I'm absolutely sure I didn't get the two NiCad packs mixed
> up....  and the initial discharge times on these packs was within 30
> seconds of each other...

> I guess the only meaningfull info here is that the NiCads have a
> higher self discharge rate....

> Jim White
> AMA 2466
> WB2WOY
> WPMPA/BCF/PFC
> SouthShoreSoftware
> Treasure Island, FL


 
 
 

Update - NiMH and NiCad in same plane....

Post by Eric Wenge » Fri, 18 Jun 1999 04:00:00


I am definitely not a battery expert, but just in my observation and from
the information posted seems that the self-discharge rate is HIGHER on the
NiMH batteries than NiCads.

Your initial testing on both batteries was performed at the C/2 rate,
therefore all the data to this point appears accurate for comparison.  What
is a little confusing is that since the NiCad was 800 mah and the NiMH was
2100 mah, that you must still compare discharge times with the load that was
placed on the batteries from the model.  Since the model has a constant
discharge rate of say 200 mah, you actually were discharging the NiCads at
C/4 and the NiMH at C/10 which appears to void the comparison.   Since there
was approximately the same amount of charge left in both the NiCads and the
NiMH after 10 days, and the NiMH has more than double the capacity of your
NiCad,  I would assume that the self-discharge rate of the NiMH to be much
higher since the initial charge was at approximately 2100 instead of 800.
Just my observation.

I am very interested in your study and would be anxious to learn of your
findings on durability and life of the NiMHs.   Good luck!

Eric
Oklahoma City, OK

--

 
 
 

Update - NiMH and NiCad in same plane....

Post by Charley & Peggy Robinso » Fri, 18 Jun 1999 04:00:00


  Heeeyyyy, some real data!  Gooodoonnyyaaa!  Thanks for sharing the
info.

  CR

 
 
 

Update - NiMH and NiCad in same plane....

Post by Jim Whi » Sat, 19 Jun 1999 04:00:00


it appeared to me that the energy used in the four flights was
insignificant as compared to the energy lost to self discharge.... and
I chose to ignore the inommaly in the data on the 800's as regards to
the flown one having more residual charge....  I'm chalking that one
up to a potential difference in initial charge time...

gonna repat the same test, better controlled, with the opposite
packs...

...my primary objective is to see if the NiMH cells are as "fragile"
as many would have us believe.... my gut feeling is that a lot of the
negative "field" reports are a result of abuse, such as in high rate
peak charging....  my goal is higher capacity to obviate the need for
field charging, not lower weight at the same capacity, requiring a
field charge.....

my initial feelings, based on my charging cycles to date, is that
temperature is gonna be the best indicator of a full charge on the
NiMH's.... not a voltage profile.... at C/10 charge, they rapidly
"warm-up" somewhere between 12 and 14 hours....  gonna instrument this
and see....  I think a temp probe blaced next to the pack will be
accurate enough.... no need for an embedded probe, since high rates
are not involved... probably try same at C/5, too.....

gonna get a AA pack to try in an "expendable" plane all by itself....
with "less than optimal" vibration isolation...

OBTW, I seriously doubt that we'll find thhat a parallel connection of
an NiMH and NiCad will result in equal load distribution....

... stay tuned....

Quote:

>I am definitely not a battery expert, but just in my observation and from
>the information posted seems that the self-discharge rate is HIGHER on the
>NiMH batteries than NiCads.

>Your initial testing on both batteries was performed at the C/2 rate,
>therefore all the data to this point appears accurate for comparison.  What
>is a little confusing is that since the NiCad was 800 mah and the NiMH was
>2100 mah, that you must still compare discharge times with the load that was
>placed on the batteries from the model.  Since the model has a constant
>discharge rate of say 200 mah, you actually were discharging the NiCads at
>C/4 and the NiMH at C/10 which appears to void the comparison.   Since there
>was approximately the same amount of charge left in both the NiCads and the
>NiMH after 10 days, and the NiMH has more than double the capacity of your
>NiCad,  I would assume that the self-discharge rate of the NiMH to be much
>higher since the initial charge was at approximately 2100 instead of 800.
>Just my observation.

>I am very interested in your study and would be anxious to learn of your
>findings on durability and life of the NiMHs.   Good luck!

>Eric
>Oklahoma City, OK

Jim White
AMA 2466
WB2WOY
WPMPA/BCF/PFC
SouthShoreSoftware
Treasure Island, FL
 
 
 

Update - NiMH and NiCad in same plane....

Post by Ib Therkelse » Sat, 19 Jun 1999 04:00:00


Quote:

> ... stay tuned....

Did you ever specify which exact brand these NiCd/NiMH were ? I tend to
believe that it might matter whether the cells are produced by a
well-reputed company versus a 'no name' company.

Ib Therkelsen

 
 
 

Update - NiMH and NiCad in same plane....

Post by Jim Whi » Sun, 20 Jun 1999 04:00:00


Quote:


>> ... stay tuned....

>Did you ever specify which exact brand these NiCd/NiMH were ? I tend to
>believe that it might matter whether the cells are produced by a
>well-reputed company versus a 'no name' company.

>Ib Therkelsen


the NiCads are Sanyo red cells.... N800AR...  the NiMH's are
"supposed" to be Sanyo.... they are green wrapped and say "made in
japan" on them....  I bought some 4/5 A cells (3500 mah) from the same
source, and they look identical, except that their capacity and a
Sanyo compatible part number is on the wrapper as well as the "made in
japan"....

Jim White
AMA 2466
WB2WOY
WPMPA/BCF/PFC
SouthShoreSoftware
Treasure Island, FL

 
 
 

Update - NiMH and NiCad in same plane....

Post by Charley & Peggy Robinso » Sun, 20 Jun 1999 04:00:00


Quote:

 SNIP

> gonna get a AA pack to try in an "expendable" plane all by itself....
> with "less than optimal" vibration isolation...

  Seems like the inevitable result will be a crashed model.  The only
question is, "How long will it take?"  Don't understand why you want to
do this.

Quote:

> OBTW, I seriously doubt that we'll find that a parallel connection of
> an NiMH and NiCad will result in equal load distribution....

  Fair enough since the internal resistance is different in the packs.
Another case of knowing the answer before you begin.  

Quote:
> ... stay tuned....

  Sure will!

  CR

Quote:

 SNIP  

> Jim White
> AMA 2466
> WB2WOY
> WPMPA/BCF/PFC
> SouthShoreSoftware
> Treasure Island, FL

 
 
 

Update - NiMH and NiCad in same plane....

Post by Jim Whi » Sun, 20 Jun 1999 04:00:00



Quote:


> SNIP

>> gonna get a AA pack to try in an "expendable" plane all by itself....
>> with "less than optimal" vibration isolation...

>  Seems like the inevitable result will be a crashed model.  The only
>question is, "How long will it take?"  Don't understand why you want to
>do this.

why so????  if I put in NiCads, the result would be the same....
inevitably, it'll crash (or maybe I'd sell it)....  might take a
hundred years, though !!

Quote:

>> OBTW, I seriously doubt that we'll find that a parallel connection of
>> an NiMH and NiCad will result in equal load distribution....

>  Fair enough since the internal resistance is different in the packs.
>Another case of knowing the answer before you begin.  

>> ... stay tuned....

>  Sure will!

>  CR

Jim White
AMA 2466
WB2WOY
WPMPA/BCF/PFC
SouthShoreSoftware
Treasure Island, FL