I’m taking a small walk mower and turning it into a tank drive r/c mower. I have two wheelchair motors. I have the controller and the wiring harness. It runs off of two 12V 55AH batteries. They are wired in series so it takes 24 volts. My question is if I can run the motors with a 24 volt alternator or do I still need a battery? If i still need a battery could use something with less Amp Hours?
Tip #1: Be really careful with this. Make sure that you always have a cutoff for both the drive and the engine… the potential for danger here is huge. Make sure that if any component of the control system fails, then the engine cutoff is triggered (that includes whatever you use to trigger the engine cutoff) ::safety::
Although the voltages match up between the batteries and the alternator, and both likely have the necessary current sourcing capability, the alternator produces AC which won’t work. Sorry, but you’re stuck with batteries (it isn’t reasonable to use an inverter to power the wheels, either).
Whether or not you could get by using a lower-capacity battery depends mostly on how long you wish to use it for at a time. FRC have batteries in a similar capacity range, and I find we can often run for 20 minutes or so at a time off of one battery (intermittantly, granted – not at competition). If you set it up and it takes forever to drain the batteries, then you can use smaller batteries :rolleyes:
Does the alternator have a built-in rectifier and voltage regulator like automotive alternators in the '80s?
The voltages match, but what is the power output capability of the alternator and the batteries?
I have been considering and RC lawn mower for a year now the biggest problem I have thought of is going side ways on a hill is very dangerous when human control isn’t involved. Which led me to think of heavy duty swerve. But at this point building a swerve mower may be nice but I’d have to machine the modules myself because I don’t think they make swerve modules for pneumatic wheels.
First, what flameout said about safety isn’t to be ignored.
Modern alternators require ‘bootstrap’ current to excite, so a battery of some sort is required, perhaps as small as 5 Ah might be enough. I’d think that even a small alternator would have the power output to run two wheelchair motors.
An alternator doesn’t have a permanent magnet, instead it uses coils of wire to create a magnetic field. These electromagnets are spun on the ‘rotor’, past the coils on the ‘stator’. The stator wiring is where the power output comes from.
Since the power generated must be 3-phase (you’ll learn why in Electrical Engineering class), it needs to be rectified (converted to pulsating DC), using diodes.
The battery not only provides the energy for that first bit of magnetic field on the rotor, it acts like a giant capacitor to smooth out much of the pulsating DC from the alternator.
Working backwards from the 55 amp hour batteries, we can expect that the total current is somewhere between 5 and 10 amps when driving. Since the need is intermittent, it might even be a little higher. However, getting the little engine to both supply enough horse power to cut grass and energize the alternator might be asking too much. Remember that the output of the alternator is a function of input power, speed and load. Depending on the size of the yard you want to cut, you might be happier with a simple 24 volt battery system and outboard charger. Two robot batteries in series might give you enough to drive the mower for at least an hour, if that works.