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Author Topic: Generator Wall Wart charger.  (Read 3322 times)
KR4VT
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Posts: 52




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« on: November 03, 2011, 09:05:16 AM »

My emergency power source is a Generac 8.5 KW gas generator with electric start. It has a 12v battery and came with an AC adapter to maintain the charge on the battery.  Unfortunately I have misplaced the wall wart style charger and the owners manual to the generator.

How can I determine the volts/amps needed for this application? I figure 12 volts will be correct but how do I determine the proper current rating?
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KB3HG
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« Reply #1 on: November 03, 2011, 09:26:00 AM »

A simple float charger is one answer,an example:  Harbor Freight  (not for AGM) sells them for about 10.00. another answer would be an intelligent charger  for more money.  Auto stores , Kmart, Wally"s World.   

Tom Kb3hg
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K5LXP
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« Reply #2 on: November 03, 2011, 09:32:37 AM »

I would check to see if there's any intermediate circuitry between the battery and where the wall wart connects.   If there's any circuitry there, either it or a connected charger may get "confused" or compromised.   If it's a straight shot then any float charger would work fine, like those made for motorcycle batteries.  I'd be leery of the "especially cheap" float chargers from the likes of Harbor Freight, as I've found they're a little too aggressive to leave connected 24/7.

One other point, Generac is a "real" company and I'd bet with a bit of digging you could find out exactly what they use for a wart, and also source a replacement.


Mark K5LXP
Albuquerque, NM
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W3LK
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« Reply #3 on: November 03, 2011, 09:37:54 AM »

Generac has both manuals and replacements parts available on their web site:

www.generac.com

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A smoking section in a restaurant makes as much sense as a peeing section in a swimming pool.
WB6BYU
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« Reply #4 on: November 03, 2011, 09:52:42 AM »

I had a similar problem with an electric-start propane backup generator for the
greenhouse - I don't use it often enough to keep the battery charged, especially
during cold weather (when I am most likely to need it.)

My solution was to take a higher voltage wall wart (possibly a 24 VAC unit - I don't
remember) and add a series diode and dropping resistor adjusted to give a relatively
low current (>10mA I think) into a fully-charged battery.  The current has to be
low enough that it doesn't over charge the battery.  Using the higher voltage
with a dropping resistor prevents the current from exceeding the rating of the wall
wart if the battery is totally dead, or when starting the generator.

This has lasted through 3 winters so far, with no starting problems.  It's just enough
to counter the self-discharge of the battery without over-charging it.  It isn't good
for recharging the battery when it is low (the generator does that) but just
maintains it.
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WX7G
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« Reply #5 on: November 03, 2011, 09:58:06 AM »

The correct way to maintain a float charge on a lead acid battery is with a voltage source and not a current source. The float current should be about 1/500 the amp-hour rating.

14.1 volts is common for automotive batteries but your battery might be different. There is also a temperature coefficient involved if you want it just right.
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K2DC
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« Reply #6 on: November 03, 2011, 12:43:41 PM »

Love my Generac, had it for 8 years now.  My transfer switches cover about 70% of the house, and I've run it for 13 hours with gas left over.  I also have the wall wart float charger and it works great.  It's never taken more than 20-30 seconds to start even after sitting cold for a considerable length of time.

Suggest you have your model number in hand (serial number might help too) and give them a call at 1-888-GENERAC (1-888-436-3722) 7 am to 6 pm Central.

73,

Don, K2DC
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KR4VT
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« Reply #7 on: November 03, 2011, 01:46:51 PM »

K2DC, can you give me the volt/amp rating for you charger?  Also, do you keep it plugged in all the time or all winter?

TNX
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K2DC
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« Reply #8 on: November 03, 2011, 02:52:38 PM »

Just got back from the garage...  My Generac is a Model 7000EXL which I don't see listed on their web site, so it may be an obsolete model.  The wall wart is 12VDC, 750 mA, + on the center conductor.  I did not measure the diameter of the DC connector, but you can get them with connector sets that are interchangeable to fit almost anything.  Mine's been plugged in over 8 years and I've never had a problem with a soft battery.  Let me know how you make out.

73,

Don, K2DC

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K0ZN
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Posts: 1553




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« Reply #9 on: November 03, 2011, 06:35:59 PM »


Strongly suggest you pick up another copy of the Owner's manual so that you can pull proper maintenance on that Genset.  The number one cause of generator failures
is related to LACK of maintenance. There are LOTS of fuel related problems with equipment that is used infrequently. Engines that spend most of their life
in a storage mode have a completely different set of problems than engines that run regularly. This is not to say that you are not properly maintaining the
generator, but my comments are just to amplify the importance of doing recommended maintenance on a generator as per the manufacturers Owner's Manual.
There is nothing worse than a generator that will not start when you need it most.

73, K0ZN
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K8AXW
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« Reply #10 on: November 03, 2011, 09:52:54 PM »

On the subject of emergency generators:

I built two heavy duty extension cords to be used with my emergency generator.  Each uses an overvoltage protection circuit to monitor and trip the GFCI receptacle if the voltage exceeds 130VAC.  I reserve these OVP devices for sensitive gear like electronics.

The article was published in the June 1994 issue of QST magazine and is available on the ARRL website for ARRL members.

A PCB is available from FAR Circuits which simplifies construction.  The parts count is low and the whole thing works like a charm.

One note:  There was one wiring modification made to the original circuit and if anyone decides to build one strongly I suggest you contact Jerry Paquette, WB8IOW and ask for this wiring change.  (His email address is available on QRZ.com.)
« Last Edit: November 03, 2011, 09:58:03 PM by K8AXW » Logged
K9KJM
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Posts: 2415




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« Reply #11 on: November 03, 2011, 10:27:52 PM »

You need a fully automatic type unit that cannot overcharge the battery.
I agree that the Harbor Freight Tools maintainer IS a good replacement:

http://www.harborfreight.com/automatic-battery-float-charger-42292.html

Note that the Harbor Freight maintainer is NOT meant to charge a weak battery!  The battery needs to be fully charged before connecting the maintainer!

Also note that the Harbor Freight maintainer is frequently on sale for 4.99, Or HALF price!   It pays to wait for that 50% off coupon found in magazines etc.

Having electric start on a generator is a very nice feature to have.   Always also have a set of jumper cables for your car handy.   In the event something happens and your electric start battery does get weak, Just jump start it with your car!

Another good idea is to get some PRI-G to add to your gas.  This stuff really works to extend the life of today's crappy gasoline:
http://www.batterystuff.com/fuel-treatments/PRIG32oz.html



« Last Edit: November 03, 2011, 10:30:29 PM by K9KJM » Logged
W5GNB
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Posts: 419




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« Reply #12 on: November 05, 2011, 08:59:01 AM »

The Wallwart for my Genrac 5kw generator is nothing more than a simple 12vdc @ 200ma device... Nothing more..  you can probably get one at Radioshack or whatever.

It simply floats the gellcell battery at full charge and that's it.......

Gary - W5GNB
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WX7G
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« Reply #13 on: November 06, 2011, 07:01:12 AM »

12 volts will not fully charge a 12 volt lead acid battery nor will it provide a proper "float." 14 volts is closer to the correct voltage.
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N6AJR
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« Reply #14 on: November 06, 2011, 11:18:48 AM »

There are a couple of ways to go here....

1.  get the "real" gizmo and replace the existing one.

2. get a small 3 stage battery charger and hook it up. I have used the Ranger brand at 750 millamps for about $30 and they work fine. ( HRO has them and they are also used for long term storage on motorcycles.)

3. pick up a small solar panel  with a blocking diode and leave it ghooked up all the time to the mbattery.  I have a couple of these, about a foot square, with a mini controller built in. They are used for  keeping the battery up on V W's in shipment. they put out 400 or 500 mills ( half a watt) or so and have a diode to block when night falls.

 I use a small ICP brand Battery Saver in my truck which I don't drive  often, (see the ones at the bottom of this link)

http://www.google.com/products/catalog?hl=en&biw=1548&bih=746&q=icp+solar+chargers&gs_upl=27671l30519l1l32727l8l7l0l1l1l0l241l1184l0.5.2l8l0&bav=on.2,or.r_gc.r_pw.,cf.osb&wrapid=tlif132060665004510&um=1&ie=UTF-8&tbm=shop&cid=5354493801661244540&sa=X&ei=4du2TrGLIYeJiAL6wex5&ved=0CHoQ8wIwAg#

I use one of the 1 foot square ones on my riding mower to keep the battery up, the battery last for 4 or 5 years  and always starts.

I hope these give yo and idea or two.
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