Fluke 750a batteries.............
Hello All,
I posted this over at the HP yahoo group as well, so pardon the redundancy if you belong to both or more.
My new to me Fluke 750a reference divider arrived last evening and I have been having one heck of a time finding info on replacement battery options others have used on their 750a's. Fluke spec'd (2) 6.7v mercury cell batteries for the overload protection circuit and these are clearly no longer available. What is everyone using for power? I am hoping to not use a separate DC supply for this app.
The only manual I can find is here:
http://bama.edebris.com/manuals/fluke/750a/ http://bama.edebris.com/manuals/fluke/750a/
I have been able to find Wein batteries that are 1.35v zinc/air and I could stack and shrink wrap 5 of those in series to arrive at 6.75 very stable volts, but they are a minimum of $4.50 each cell. I was hoping to find a more affordable / elegant solution.
Will the circuit handle (2) 3.6v Li-Ion in series instead?
Any thoughts?
Cheers,
David
On 09/25/2015 08:53 AM, David Garrido wrote:
I have been able to find Wein batteries that are 1.35v zinc/air and I
could stack and shrink wrap 5 of those in series to arrive at 6.75
very stable volts, but they are a minimum of $4.50 each cell. I was
hoping to find a more affordable / elegant solution.
Zinc-air won't work. Once the seal is broken, the lifetime is measured
in days. BTDT.
The unit is probably relying on the batteries as a voltage reference so
you really need the mercury batteries unless you want to design a stable
reference.
Fortunately Mercury batteries are still available from Russia.
The guy has a good rep.
John
--
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Tellico Plains, Occupied TN
http://www.fluxeon.com <-- THE source for induction heaters
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PGP key: wwwkeys.pgp.net: BCB68D77
The usual solution is to find an alkaline pack that gives you a
few volts more than you need, and use a voltage regulator to
regulate down to the desired voltage.
The rub becomes finding a voltage regulator that gives you the
magic combination of accuracy and stability that you need for
your application.
In this case (I don't have the schematic in front of me) it doesn't
sound like the mercury cells are being used for their modest
stability, but rather for their compact size, and long life.
Regulation might not be all that necessary.
Drop Wein cells from your memory bank! The only thing they are
suitable for is hearing aids, and only because they have a near
infinite shelf life, as long as the tab isn't pulled. Once the tab
is pulled, they consume oxygen from the air around them, and make
water vapor.
Some misguided folk have specified them for use in Accutron watches,
where they quickly use up all of the oxygen in the watch case, and
replace it with much needed moisture to help the watch parts rust.
-Chuck Harris
David Garrido wrote:
Hello All,
I posted this over at the HP yahoo group as well, so pardon the redundancy if you
belong to both or more.
My new to me Fluke 750a reference divider arrived last evening and I have been
having one heck of a time finding info on replacement battery options others have
used on their 750a's. Fluke spec'd (2) 6.7v mercury cell batteries for the
overload protection circuit and these are clearly no longer available. What is
everyone using for power? I am hoping to not use a separate DC supply for this
app.
The only manual I can find is here:
http://bama.edebris.com/manuals/fluke/750a/
http://bama.edebris.com/manuals/fluke/750a/
I have been able to find Wein batteries that are 1.35v zinc/air and I could stack
and shrink wrap 5 of those in series to arrive at 6.75 very stable volts, but they
are a minimum of $4.50 each cell. I was hoping to find a more affordable /
elegant solution.
Will the circuit handle (2) 3.6v Li-Ion in series instead?
Any thoughts?
Cheers,
David _______________________________________________ volt-nuts mailing list --
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instructions there.
David,
I have a (recently purchased) 750A as well, but haven't used it yet. I have
the same problem with the batteries. I found this post in the archives from
2012:
On 11/22/2012 7:49 AM, Steve Smith wrote:
<snip>> Regarding the 750A batteries:
I replaced mine with four ER14250/LS14250 1/2AA 3.6V 1200mAh lithium
cells. Remove the original mercury battery holder and replace it with
a dual AA cell holder. Use the kind that has the batteries
side-by-side because you need to connect to the center tap between the
cells. Wiring is pretty much identical to the way the mercury battery
holder was wired. Install the lithium cells in a series string and you
have +/-7.2V which is a bit higher than the +/- 6.75V of the mercury
batteries but still works. The lithium cells have slightly more mAh
capacity than the mercury cells and a much longer shelf life which
works well for the 750A as the protection circuit draws very little
current. Don't disable this protection circuit, it's too easy to fry
the divider string if you're not paying attention.
Thanks - Steve
My guess is that the trip voltage will be changed a little bit, but not
enough to allow damage in case of overload. Sounds like a reasonable
solution
Cheers,
Dave M
David Garrido wrote:
Hello All,
I posted this over at the HP yahoo group as well, so pardon the
redundancy if you belong to both or more.
My new to me Fluke 750a reference divider arrived last evening and I
have been having one heck of a time finding info on replacement
battery options others have used on their 750a's. Fluke spec'd (2)
6.7v mercury cell batteries for the overload protection circuit and
these are clearly no longer available. What is everyone using for
power? I am hoping to not use a separate DC supply for this app.
The only manual I can find is here:
http://bama.edebris.com/manuals/fluke/750a/
http://bama.edebris.com/manuals/fluke/750a/
I have been able to find Wein batteries that are 1.35v zinc/air and I
could stack and shrink wrap 5 of those in series to arrive at 6.75
very stable volts, but they are a minimum of $4.50 each cell. I was
hoping to find a more affordable / elegant solution.
Will the circuit handle (2) 3.6v Li-Ion in series instead?
Any thoughts?
Cheers,
David
As it happens, in this case, the batteries are only
a very poor reference. They use the 6.75V to feed a
voltage divider to compare the voltage in the main
divider chain against. They are looking for a switch
action to happen over about a 30% range.... not really
all that critical.
Mercury oxide batteries weren't all that stable even
when they were in vogue. They were 1.35V, and dropped
down to 1.2V when you ran them at rated current. It
is easy to duplicate their performance with just about
anything in a regulator... a couple of transistors and
a zener can do a better job.
Anyone that used to use mercury cells should completely
erase Wein cells from their memory. Other than making
about 1.35V, they are utterly incompatible with mercury
oxide cells.
Wein cells last about 3 or 4 weeks if they have plenty
of O2, and you draw no current. They release moisture,
which can cause problems with some applications. They
are about perfect for a hearing aid, as it is already
a moist environment.
-Chuck Harris
NeonJohn wrote:
On 09/25/2015 08:53 AM, David Garrido wrote:
I have been able to find Wein batteries that are 1.35v zinc/air and I
could stack and shrink wrap 5 of those in series to arrive at 6.75
very stable volts, but they are a minimum of $4.50 each cell. I was
hoping to find a more affordable / elegant solution.
Zinc-air won't work. Once the seal is broken, the lifetime is measured
in days. BTDT.
The unit is probably relying on the batteries as a voltage reference so
you really need the mercury batteries unless you want to design a stable
reference.
Fortunately Mercury batteries are still available from Russia.
The guy has a good rep.
John
Four Tadiran 5955 2/3 AA lithiums have worked fine for me. They come with
leads that I just soldered onto the battery holder terminals.
Hello All,
I posted this over at the HP yahoo group as well, so pardon the redundancy
if you belong to both or more.
My new to me Fluke 750a reference divider arrived last evening and I have
been having one heck of a time finding info on replacement battery options
others have used on their 750a's. Fluke spec'd (2) 6.7v mercury cell
batteries for the overload protection circuit and these are clearly no
longer available. What is everyone using for power? I am hoping to not
use a separate DC supply for this app.
The only manual I can find is here:
http://bama.edebris.com/manuals/fluke/750a/ <
http://bama.edebris.com/manuals/fluke/750a/>
I have been able to find Wein batteries that are 1.35v zinc/air and I could
stack and shrink wrap 5 of those in series to arrive at 6.75 very stable
volts, but they are a minimum of $4.50 each cell. I was hoping to find a
more affordable / elegant solution.
Will the circuit handle (2) 3.6v Li-Ion in series instead?
Any thoughts?
Cheers,
David
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