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-   -   Voltage reducer, 36 -> 18 volts (https://www.buggiesgonewild.com/showthread.php?t=103568)

jdunmyer 03-09-2015 04:13 PM

Voltage reducer, 36 -> 18 volts
 
I have a GE ElecTrak garden tractor that's about the neatest toy since my RXV, but it has an anomaly that I'd like to correct.

These things use a 1970's vintage GM window lift motor for the power implement lift, running on 18 volts instead of 12. When plowing snow, the lift gets a real workout, and it tends to imbalance the batteries.

I have a set of batteries that I put in my old CC in 2013, so they're in very good shape. Today, I measured the voltages and found 3 at 6.42 and the other 3 at 6.38, with the lower ones being the set that powers the lift. It's been a week or more since I plowed snow, and it's been charged, but I didn't let it sit on charge for a very long time, maybe only a couple or 3 hours. I have an EZ-Go Total Charge charger with a green front and an added golf cart receptacle, so let it cycle through today; it took 2 or 3 hours before it shut off. Charge rate started off at less than 5 amps.

The lift motor draws nearly 15 amps with the plow, and will probably use more with the snow blower. It is very slow on 12 volts, so using my existing 30 amp reducer is out, it really needs the 18 volts.

Any ideas? I don't need real good voltage regulation, but using a simple dropping resistor won't work, as the current draw is much less when the lift is going "down", as in < 10 amps. When I asked on the E.T. forum about battery imbalance, one of the old-timers said that it's more a theoretical problem than a real one. It probably won't be much of a problem with the mower, as it'll not be up and down like the snow plow is.

Volt_Ampere 03-09-2015 04:24 PM

Re: Voltage reducer, 36 -> 18 volts
 
It should rebalance after a couple charges. Current draw is too much for any standard reducer and if you want 18 V, you probably already have the best easy way to do that.

yurtle 03-10-2015 06:59 AM

Re: Voltage reducer, 36 -> 18 volts
 
You can also change the batteries it uses seasonally, (or weekly-depending on where you live) to even out the load.

jdunmyer 03-10-2015 07:15 AM

Re: Voltage reducer, 36 -> 18 volts
 
Yurtle,
It's not easy to switch the batteries that the lift uses: one end is buried within the control panel wiring, the other is connected to one of the batteries. It would require actually removing and shuffling the batteries.

Another alternative would be to use a regular battery charger on the "low" batteries.

I hadn't really figured on actually using the tractor, just playing with it, as my yard is a couple of acres or more and rather rough. Plus, I have a Diesel tractor with a 60" mower to cut it. However, I picked up a snow blade and added tire chains, and I really can't believe how well it works. I didn't have the chains for the first and largest snow of the season, but I'm pretty well set for next year, only have to add a bit of weight to the rear.

Been thinking about using a big ol' resistor of some sort. There would be NO voltage regulation, but it might work OK. Maybe a 30-amp 18-volt Zener diode in series? (if such a thing even exists)

JohnnieB 03-10-2015 02:25 PM

Re: Voltage reducer, 36 -> 18 volts
 
If the garden tractor has a 6 x 6V battery pack and you need 18V, you might be able to add some battery isolators (aka steering diodes) and put two sets of three batteries in parallel for 18V, without altering the regular series (36V) used by the tractor drive system. However, if the tractor uses a frame ground, it probably cannot be done.

jdunmyer 03-10-2015 02:44 PM

Re: Voltage reducer, 36 -> 18 volts
 
JohnnieB,
You're a genius, I bow to your knowledge! <<grin>>

The frame of the tractor is isolated from ground, just like a golf cart, and it does use 6 X 6V batteries.

Will have to research "steering diodes", it's been about 50 years since I graduated electronics school.

Thanks for the tip!

<<Jim>>

JohnnieB 03-10-2015 03:05 PM

Re: Voltage reducer, 36 -> 18 volts
 
A "steering diode" is how the diode is used in the circuit rather than the device itself.

The commercially available :Battery isolators" are steering diodes packaged in a pretty box and cost an arm and leg, but a power rectifier type diodes can be used. You said the lift used about 15A, so I'd go with at least 50A diodes, with at least 100V PIV.

Volt_Ampere 03-10-2015 03:10 PM

Re: Voltage reducer, 36 -> 18 volts
 
Sorry but I don't see how that works when the batteries are hard wired in series.

jdunmyer 03-10-2015 03:49 PM

Re: Voltage reducer, 36 -> 18 volts
 
JohnnieB,
I'm aware that the term "steering diode" describes its function, not the device itself. Somewhere in my "stash", I have the entire rectifier assembly for a welder of some sort. IIRC, it has several VERY heavy duty diodes attached to a largish heat sink.

Would the voltage drop from the diodes cause any trouble during charging?

<<Jim>>

Volt_Ampere 03-10-2015 04:27 PM

Re: Voltage reducer, 36 -> 18 volts
 
I know what they are but I don't see how you can get parallel 18 volts at the same time you have series 36 Volts to run the cart.


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