[Spudland_Dave]

Anybody know of a good "automotive grade" 12v voltage regulator which would regulate a 12v battery down to 8v?
Heres the scoop...FIL is looking to replace the 6V battery on his 420C, a common "old timer" trick is to install an 8V battery, FIL was saying its pretty much any old 6v machine up home has an 8V battery in it....starts perfectly and you dont need to modify anything.... We were brainstorming that it would be easier to use a 12v battery because they're cheaper & easier to find, AND you can boost em/charge em much easier.

 

[eepete]

What's the range of output current you need at 8V?

Pete

 

[Spudland_Dave]

What's the range of output current you need at 8V?

Pete

ummmmmmmm.....I dunno:think::lol:

 

[eepete]

Ok, well, if this is being used to run a starter motor, then that current might be in the 400 amp range? Currents are higher with 6V stuff than 12V stuff. So you're trying to drop 13.8 volts to 8 volts. If you use a linear regulator ( or for that matter a resistor), then you have a 5.8 volt drop times a 400 amp load. That means the regulator, however it is built, needs to dissipate 2320 watts. That's a big .0025 ohm power resistor. Of course if this is running a tractor, then a power resistor can't be used since what would work when starting would provide just about full battery voltage under a light load.

So now you're looking for a transistor regulator, and 2320 watts means a lot of big transistors. So then you start looking at switching regulators and you're still looking at a lot of big transistors and some honkin' inductors and caps.

Generally speaking, any regulator that puts out more than 10 amps gets expensive, and more that 100 amps is really expensive.

400 amps is right out.

Of course I'm thinking all this while my brain is in SWAG City, lots of assumptions here on my part. Bottom line: I can think of now cheap way to regulate a 12V battery down to 8 or 6 volts and get "battery-like" performance out of it over all the current ranges that a tractor needs.

Sorry... :empathy3:

Pete

 

[Music Man]

I was in Sams Club recently and noticed that they had 8v batteries sitting along side their 6v golf cart batteries. If there is a Sams Club near you it might be worth a try. I remember using the 8v in the first Olds V8's because 6v didn't turn them fast enough to start.