Skip Douglas SkipD
Several folks have recently been interested in how a battery maintainer charger works and what the charging rates are, etc. This morning I made a few measurements and felt that y'all might be interested in the results.

First of all, a little background: My generator is an early 2008 production version of an 18 kW (on natural gas) Generac model 5416. In the first few months of operation I discovered that the electrolyte levels in the battery were going down at an unacceptable rate. Considering the battery explosion incidents we were reading about here in that time frame, I decided to completely disconnect the Generac battery charger (bolted into the generator next to the controller board) and replace it with a [URL="http://www.batterychargers.com/ProductDetail.aspx?ProductName=94026501A"][COLOR=Blue][U]Schumacher SE-1-12S battery maintainer[/U][/COLOR][/URL]. I provided power for the charger and for a battery blanket by installing a 20-amp 120VAC receptacle in my generator's battery compartment. In the last two plus years, I've only had to add 1/8" of water to some of the cells in the battery on one PM check.

Now to the performance characteristics of the Schumacher battery maintainer when the generator has been at rest:
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[*]I used two [URL="http://www.atecorp.com/equipment/fluke/8060a.asp"][U][COLOR=Blue]Fluke 8060A[/COLOR][/U][/URL] multimeters (the top of the Fluke handheld DMM line in their day), one equipped with voltage sensing leads and the other equipped with a [URL="http://www.fluke.com/fluke/usen/accessories/current-clamps/i1010.htm?PID=56281"][U][COLOR=Blue]Fluke i1010 AC/DC Current Clamp[/COLOR][/U][/URL] to measure voltage and current simultaneously.
[*]When the generator has not run for at least a day or two, the maintainer cycles approximately once each two minutes (1 min 50 seconds measured).
[*]Charging cycle on-time was measured at roughly 13 seconds.
[*]Battery terminal voltage is at about 12.88 volts when the charger starts its cycle. The voltage is what triggers the charger cycle.
[*]At the end of the cycle, the battery terminal voltage was about 13.9 volts and it very quickly dropped off to about 13.0 volts.
[*]Over the next minute and a half, the battery voltage slowly drops to about 12.88 volts and the next charge cycle starts at that level.
[*]The charger output current is about 1.2 amperes when the cycle is running.
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I ran an additional set of tests. While both of my meters were connected, I started the generator and ran it (with no load) for a few minutes. Here are the measured results:
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[*]The battery voltage was approximately 12.25 volts DC just after starting the generator and started recovering immediately (because the maintainer had started its charging cycle).
[*]While the engine was running, the battery maintainer output was approximately 1.9 amperes.
[*]After stopping the generator's engine, the charging current rate from the battery maintainer reduced over a minute or two to about 1.4 amperes.
[/LIST]
I hope this information is useful to folks on the forum here.
Skip Douglas
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Canada_Guy
Very interesting post Skip. Thanks for taking time to make these measurements and posting your results.

I note one thing of interest. There is 1.9 amps from the charger/maintainer while the generator is running.

This exceededs the 1.2 amps that the Generac charger appears to be capable of (my measurement of what the charger was producing while the generator was running) and exceeds the 1.5 amp rating of the Schumacher charger/maintainer.
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Geoff Z
Skip, do you mind posting the make and model of your battery, along with the CCA & CA?
Thanks.
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Skip Douglas SkipD
Kelly Myers;11307 wrote:
Skip, do you mind posting the make and model of your battery, along with the CCA & CA?
Thanks.
The battery, supplied by the local Generac dealer who installed it, is a Werker 26-ULT. It's a conventional group 26 wet cell battery with a CCA rating of 525. The only other rating I could see on it is: RC Mins@25A = 80.

This is a brand that I've never seen before. I cannot find one by searching via Google.
Skip Douglas
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douglas123
Skip, You said the brand was Werker. Can you say Batteries PLus Dealer. I use a lot of them for the Briggs home standby sytems most common are 33ah and 55ah. Older models used 33 because of space contraints and new models use the 55 plenty of room in the back end. Sealed AGM to keep from sucking corrosive gas into the gen end.
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Skip Douglas SkipD
I did hit on the relationship between Werker and Batteries Plus, but could not find my battery listed in current web sites. They now use a different brand name for their group 26 batteries - Rayovac.
Skip Douglas
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douglas123
Next time I go by Batteries plus I will double check and see what they are offering in the south.
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Skip Douglas SkipD
Remember that this battery was new to me in May of 2008. I wouldn't be at all surprised that better contracts are made between suppliers and stores from time to time.
Skip Douglas
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