PV: Re: Ryobi charging

["David & Sheila Knapp" <solar@aeroinc.net>]

We charged our Ryobi from two 14 watt amorphous PV modules we got from Real Goods in 1994.  It came as a kit and used a 1/4 inch headphone jack and a five amp fuse cartridge connected directly across the 24 volt 15 A-H battery bank.  The PV side used the mating headphone plug and the amorphous PV modules wired in series.  I added an analog 24 volt voltmeter and 5 amp current meter to monitor the situation.  The whole project is well documented in December 1995 of Home Power magazine under Homebrew if I remember right.  I had a lot of fun with it because It was something I could do without messing it up too badly.

In hindsight, I should have had a 3 amp diode in series with the PV array to prevent nighttime self discharging.  It took three days of FULL sun to recharge the mower, but usually a week for me in the cloudy mid-west.  The original 15 A-H batteries only lasted 3 years with this setup (as you could imagine).

After two years, one of the PV modules self destructed (aluminum foil wires to the junction box - all made in Croatia!).  I then started using the built in charger in the Ryobi, plugged into our PowerStar inverter.  We are talking triple efficiency losses here as it took about 60 amp-hours from our small 12 volt house system to replenish the 15 A-H of the 24 volt charger (about 50% efficiency).

When the original Ryobi batteries died, I replaced them with 17 amp-hour (same case size) batteries from Batteries Plus.  Three years later they have twice the capacity of what the original batteries did at three years of age.  Keeping the mower on the charger has a 7 watt phantom load after it is recharged, but it keep the battery trickle charged at 29 volts and the life is greatly extended.

Oh yeah, plan on sharpening that mulching blade every 4 - 6 mowings unless you want to draw more amp-hours.  After almost six years I can do it without loosing a knuckle!!!

Fortunately we will only have the wild flowers to contend with on our future SW Colorado building site and I will never again have to harvest a weekly crop that never goes to market!  My current neighbors all have 18 horse tractors to mow their 1/3 acre lawns and cannot understand why I mow mine by hand with something not powerful enough to finish the job on one charge (when I have vacation grass!).  Personally I enjoy the quiet of an electric mower, but look forward to swapping that time with more work in our raised vegetable beds.

Dave

_________________________________________________

David & Sheila Knapp 
Winnebago, Illinois
http://www.geocities.com/renewables/
_________________________________________________

----- Original Message ----- 
From: "Thomas M Hughes-Lampros" <tlampros@UDel.Edu>
To: "David & Sheila Knapp" <solar@aeroinc.net>
Sent: Tuesday, January 23, 2001 10:54 AM
Subject: Ryobi charging


> Hi David and Sheila,
> 
> I inherited a Ryoi mower from a friend and I've got several PV panels
> around.  How did you wire the charging for the mower?  Did you invert then
> feed the carging port or directly to the battery?  Any reverse
> current prevention for the modules?  I'm converting an old Rabbit to
> electric with a kit from ElectroAutomotive, and I plan to use PV to
> recharge it too, so the Ryobi will be a good foot-wetter.  Maybe you could
> post to the list...
> 
> After working in thermal for ~3years back in the '80s, and working in PV
> for ten years (AstroPower/Solarex/IEC) I am just now getting to putting
> thermal and PV panels on our house.
> 
> 
> Keep it up,
> Tom
> 
> Tom Hughes-Lampros tlampros@udel.edu
> Institute of Energy Conversion tel: 302.831.3523
> University of Delaware fax: 302.831.6226
> Wyoming Rd.
> Newark, DE 19716
> 
> When we turn our face to the sun,
> we feel the power to heal the earth.
> 
>       First they ignore you
>      Then they laugh at you
>         Then they fight you
>                Then you win
> 
>                     -Gandhi
> 
> 
> 
> 

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