Golf Carts – Overview
One of 4QD’s principal markets is ride-on golf carts or buggies. Now there is a different market for buggies in UK as opposed to the USA. Most American machines use petrol engines and the buggies are two or more person vehicles. There are a few electric ones, but petrol is certainly more common. For the most part the electric ones use series-wound motors (in FAQ section) which are less efficient than the permanent magnet motors used on most British machines. PM motors are usually smaller than series wound so are used mainly for the smaller vehicles (one man ride-on machines) – which this page aims to cover.
Buggies range from small, lightweight three wheelers up to more substantial four wheelers.
How do they work
The motive system in the buggies is typically two 12V batteries (to give 24v), two motors (one driving each rear wheel) and a controller to vary the power to the motors. There will also be various hand or foot pedals, levers and switches for you to tell the controller what you want fed to the motor. Now this may sound quite simple, but electronically controlling a motor is not so simple in practise. The controller works by what is called ‘pulse width modulation’.
The controller rapidly switches the battery power to the motor on and off. Typically the battery voltage is applied to the motor 20,000 times per second in a series of pulses. If the ‘on’ time is equal to the ‘off’ time then the 24v battery is connected to the motor for 50% of the time, so the motor is fooled into thinking it only has 12v across it, so it runs at half speed. If the pulse (the on time) is wider then the battery is connected for more than 50% of the time, so the motor has more voltage across it. With a narrow pulse, the voltage is reduced so that, by varying the width of the ‘on’ pulse (hence Pulse Width Modulation), the average motor voltage can be adjusted between zero and full battery voltage, varying the motor speed.
All quite simple you may think – except that to get a 15 stone man on a golf buggy up a 30% hill at 8 mph may take 100 amps or so. Electronically 100 amps is a lot of current and takes a lot of switching. Another problem is what happens if you get a wheel stuck. A pair of motors which can take 100 amps for a minute or so to get you up the hill might take 300 amps or more when stalled. If the controller isn’t designed properly this overload current will destroy it so if you want to be really unpopular when taking your buggy for a test drive, try stalling it – run it up against a brick wall and put the throttle on full. The control system must be able to take this.
A good controller will have what is called ‘Regenerative braking’. When you brake your car hard the brakes get very hot as they dissipate the car’s energy during the braking. An electric motor can however also be used as a generator and a good control system will use this fact to brake the vehicle. Instead of wasting the energy as heat, the controller tries to pump it back into the battery to save energy. The process isn’t very efficient, but some energy does get saved. More importantly it does give you single foot (or hand) pedal control operation of the vehicle. In a machine with regen braking you will find than you don’t use the mechanical brake: in fact some manufacturers do not even fit one. We always recommend to our customers that a mechanical brake be fitted as a back up safety device. Better to have an extra brake and not need it that to need one and not have it.
Then there is an electromechanical brake …. another ‘buzzword’. Some vehicles have this – others do not. A motor can only act as a generator when it is actually turning. The faster it is turning, the better it is at generating, so the harder it can be used as a brake. The opposite of this is that the motor is no good as a brake at zero speeds, so if you park your machine on a hill it will gently roll off downhill when your back is turned. To stop this, motor manufacturers can fit an electrically operated brake onto the motor. This is a small disc brake operated by a spring and held off by the controller applying 24v to an electromagnet to release the brake when it is operating. The controller removes power from the brake magnet after it has reduced the vehicle speed to zero, parking the motor.
What size buggy do I need?
This depends on your weight and the ‘hillyness’ of the courses you use. The steeper the hill, the harder the buggy has to work. The heavier you are, the harder the buggy must work. Make sure you try it out on a steep hill. If the buggy is too small for you it will loose speed on a steep hill. If it sails up the hill without any sign of a struggle – then it is OK – but make sure you have you normal full set of clubs aboard.
Most golf buggies have reversing, but how often will you use reverse on a golf course? A controller with reverse is more expensive than one without and this will add to the machine’s cost. Be sure to test the effect of operating the reverse switch when you are travelling at full speed. Some inferior controllers cannot take this and will blow up. Our reversing controllers have what is called ‘dual ramp reversing’: when you operate the reverse switch at full speed the controller will slow to a stop (at a preset, and adjustable, deceleration rate) then start up backwards, under full and safe control at all times.
Electronics and water do not mix: if the controller is mounted in a bad position and you drive through a puddle – or even on wet grass – the controller will get splashed. There is one machine of Polish manufacture which has the controller mounted very low, between the back wheels. If water gets splashed into the controller failure is very likely. The controller should in any case be adequately splash-proofed. Another point to watch is the wiring. What will happen if water drips onto any exposed cables (for instance the wire connecting the handle-bar controls to the main controller). Will the water run down the cable and end up inside a connector, or even in the main controller?
These, unfortunately, are the weak link of electric vehicles. The batteries are not the same as car batteries. Car batteries are designed for a short, hard blast (when you start the car) and a fairly quick recharge after which they are kept topped up to a sensible voltage by the car’s regulator. A battery for an electric vehicle is different because if is going to be steadily discharged then slowly recharged, going through a cyclic charge-discharge process. They are therefore sometimes called ‘traction’ batteries or ‘deep discharge’ batteries. They are more expensive than car batteries. They also have to be treated carefully: discharging them too far can damage them as can overcharging them. You also must not leave them discharged for any length of time, but should recharge them as soon as possible after use.
Lithium ion batteries are now popular replacements for lead acid batteries. They combine excellent capacity with light weight but have a couple of drawbacks. First the must be charged with a charger designed for lithium batteries. Secondly, some have undervoltage protection circuits built into them. We have seen a couple of cases where these circuits disconnected the battery when the owner was starting up a hill.
Some sort of battery voltmeter or Battery Condition Meter can be useful to tell you the charge left in them (4QD’s LED BCMs). The problem is that the batteries loose their capacity steadily: each time they are used they will accept slightly less charge on the next occasion. So there is going to come a time when a set of batteries which used to get you easily round the course indicate a low charge at the 17th hole. What do you do then? Many buggy manufacturers find than a low battery indicator causes more worried customers than it cures, so do not fit them. If you do have one fitted it will probably dip as you go up a hill. If you know that this hill always causes a certain dip, but today there is more dip, then your batteries are probably on their way out, so the indicator can be useful.