Bob's Homemade Battery Charger
 "Make-A-Volt”  Model 5-12, Serial # HM-2

The following project and article were constructed by my good friend Bob "KC9BUZ".  For the time being, questions and comments can be sent to me, and I will forward them to Bob.


    I built this charger in the spring of 2005. It was based of a similar charger that I saw in the early 1980s at Nevin Park Raceway in Corydon, Indiana. I had seen some plans for similar units on the Internet. I started to seriously research this project in February and began to collect parts. The engine was given to me this spring, it had been removed from a broken garden tiller. It is a 5 H.P. Briggs & Stratton.

    The first thing that I did was to mount the engine on a wood pallet and get it running.  It had a broken flywheel key and needed a set of points. Some tinkering, a bit of online reading, and a couple of trips to the hardware store had it running fairly well a few days later. A trip to the junkyard produced an alternator from an old Chevy. I bought a 5" diameter pulley at the local farm supply store.

    I wanted to make sure the machine would work before I spent much time or money on it. Now it was time to mount the engine and alternator to the pallet and rig up a drive belt. I sawed up some more pallets for some lumber and made some rough mountings from scrap metal. And old power steering belt from my truck coupled it all together, After things were fastened down, I wired the alternator using scrap wire and a headlight switch from a Dodge van. And old battery was attach to the contraption for the test run. Above photo: Everything it put together and ready for a test run.

    All of this hardware was quite a sight. I checked the belt alignment and tension, it was time to try the thing out. I pulled the starter rope, the engine flooded and needed a shot of starting fluid to get it going. After it warmed up a minuet, I turned the switch on. The engine sound changed and the thing was producing electricity! The engine had a burned out muffler and was very loud under load. I was surprised that it worked the first time. I had to brace the belt tensioner and generally tighten things up to get everything to run true. The machine was made of junk, but it worked. I ran the machine in this state for around a total of ten hours over a few days using it to power inverters and charge a battery.
    The engine turns at aprx. 3100 R.P.M. at full throttle and it will charge at idle speed with reduced current. The alternator turns at about 5000 R.P.M. at full throttle. The 5" pulley gives nearly 50% overdrive to the alternator. The wooden test mounting really saved a lot of work as I could easily change things as needed. I experimented with pulley size and control circuits until things were ready to make more permanent. After some more testing, I decided to make a real project out of it. The rig looked like something from the "Green Acres" television show, but it was working.


     I decided the mount the charging rig on a cart that my Grandfather Clifford Pitts built in either the late 1940's or early 1050's. I t was part of a homebuilt air compressor that he used in his shop for years. I remember seeing him use the compressor as a boy and wanted to build my charger on his old cart. Grandpa was a machinist who could make, build, or fix almost anything. Above photo: The charger in July of 2005.

    In spirit of poor-boy engineering, I decided to make everything I could out of material that I could find or free or at very low cost.

Here is what I ended up using:
  - The engine is a 5 H.P. Briggs & Stratton. It is pre 1985. It runs well but uses oil, this is not a problem since it was free.

  -  Most of the angle iron was recycled from bed frames left out for the trash on junk day in a near by town. "Curbside Shopping", price = zero dollars.
  -  The metal plate that carries the engine and alternator was from a window cut out in an electrical panel. A friend sheared it to size at his shop.

  - The battery was from a ford truck. It sat around for several months and was completely dead. I "rejuvenated" it with a homemade desulfater -1/2 wave charger that I build from a transformer out of a lamp and a diode.

  -  The alternator is a Delco 40 amp that a local rebuild shop set up for me. I started with a 78 amp unit but had problems with engine stalling under load. When I changed to a smaller drive pulley the speed was too low for adequate cooling. Below photos: The Delco alternator.

    The charge on switch controls the rotor current to allow starting the engine with no electrical load on the alternator. After the engine is up to speed, closing the switch starts charging. The switch can be opened to stop charging and prevent battery discharge from the rotor current draw. A knife switch disconnects the battery when the machine is not in use. I connect a Redi Line motor generator or a Vector inverter to supply 120 volt power. I plan to mount one of these to the cart frame.

Testing Results and Different Uses

    What is it good for? I built it to do several jobs. It can jump start a vehicle with it's on board battery, and or supply 12 volt power to an inverter to operate power tools and lights. The unit has powered my electric drills, grinder, sawzall, and rechargers for cordless tools, It does an excellent job of powering my ham radio equipment as the battery will last several hours and a short engine run will recharge it with minimal noise and fuel consumption.

    The machine does best as a charger. I ran a test by powering two 13 watt fluorescent trouble lights from an inverter for 25 hours. A twelve inch B.& W. TV was added for another two hours. When the inverter alarmed on low voltage, I ran the engine for about an hour to fully recharge. This took around two quarts of gas. This is much better fuel economy that a conventional generator that would have burned almost 15 gallons to run this small load for the same time. Speaking from experience, listening to a generator run all day gets old quickly after a while on a job site or during a five day power outage.

    The machine is labeled " Make-A-Volt" Model 5-12, Serial #HM-2. This represents 5 H.P., 12 volts, home made #2. H.M.-1 was a deep cycle group 27 battery mounted with a 300 watt inverter that was built in 1999. It has worked well for a variety of tasks and is still in use. Machine H.M.-3 is in the planning stage now. Below Photo: The name plate.

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