Battery Eliminators What are they and how do they work? Battery eliminators were first used by Lucas in the 1960s. In those days batteries were of the ‘wet’ lead acid type and did not have the safe venting that today’s batteries do. If the bike fell over on its side acid would spill, damaging the bike, also if you had an “off” you too could get covered in acid. Charging systems were very crude, most 6 volt systems did not have a voltage regulator and would often boil the battery dry leaving the bike unable to be started. However it was in competition use where the problem of acid spill became a major concern and this drove the search for a safe alternative. Simply removing the battery does not work as there is no reserve of power keep the ignition powered during kick starting and at idle. It was found that a capacitor will store just enough charge to allow the engine to catch and start without the need of a battery, ideal for competition use as not only are capacitors acid free but they are extremely light weight (lighter than even modern lithium batteries). Soon the idea was used on road going machines to give them an ‘emergency start’ function for when the battery failed. On modern machines that have voltage regulators a capacitor or battery eliminator as they are commonly known are still a useful option. In some cases not only is energy for the ignition needed but all voltage regulators need a steady reference to be able to control the system voltage. Without this they tend to become erratic and unable to control reliably. Engines change their rotational speed greatly in just one revolution of the crank shaft and hence the output of the generator changes just as quickly. This constantly and rapidly changing voltage is too much for the regulator to control without something to damp down the fluctuations and provide a steady reference. Larger ‘retro’ style with screw terminals. Order number BE2

There are a few myths surrounding battery eliminators that need to be dispelled. Some suppliers claim that their eliminator will stop the lights pulsating or flickering. The flickering light is due to the low generator output at idle and the different speed the crank is turning at on compression and power strokes, this will always happen without a battery fitted and the effect will be most pronounced on single and twin cylinder machines. Next, using a capacitor will 'off-load" the charging system or make the ignition work better, sadly this too is untrue. A battery eliminator will not affect the ignition in any way. Voltage regulators dissipate power not used by the the electrical system as heat. If there is no battery absorbing power, the regulator will dissipate this unused power as heat, therefore the load on the system is still exactly the same. Be cautious of people claiming your charging or ignition are improved with their battery eliminator as this is just not possible. Capacitors are designed for specific applications so choosing the right type is important. For example a high quality audio capacitor will cost a lot of money but will degrade in a very short time on a motorcycle as its not designed for the rigours of a charging system. ‘General purpose’ capacitors are very cheap but tend to be for mains power supplies where the voltage is always steady, again these will degrade much quicker than their ©All rights reserved. Rev 2 Oct 2016

Battery Eliminators stated life if used on a motorcycle system. For maximum life a capacitor designed for rapidly fluctuating power supplies is needed. Spending a lot of money does not guarantee you get the right type, in fact you can end up with something very unsuitable. Similarly there is nothing to gained be fitting a huge capacitor, remember the function is to either store enough power to keep the ignition alive during kick starting and at idle or to steady a voltage regulator. To stop lights flickering the capacitor would have to be so large it would be the same size or larger than the battery. Once you get over 15,000uF there is little to be gained in performance and in fact fitting a very large capacitor could even be dangerous as it will cause high power surges when lights are switched on and off. An ideal size is 6,400 - 15,000uF. There are some disadvantages in using a battery eliminator, firstly removing the battery will mean that the electrics run direct from the generator therefore when the engine is off you’ll have no lights. Also when the engine is idling there is only enough power the ignition so the lights will be very dim and indicators, horn etc will not work, sitting at a junction you may not be visible at night. Raise the revs above idle and everything works normally. In some Countries the lights must work with the engine off - this can’t happen with a battery eliminator as they do not produce any power. As no power is produced, electric starters won’t work either. What a battery eliminator does is to remove the need for the bike to carry a bulky battery, it will allow the engine to be kick started and make the system simple but basic, ideal for off road machines for example. On the plus side, the charging system becomes maintenance free as eliminators never need charging and work even after long periods of disuse. When you buy from Rex's Speed Shop you can be sure we use a modern, rugged part that is proven to be reliable in service. Battery eliminators work on permanent magnet generators, 6 or 12 volt, positive or negative earth. Its impossible to say if it will work well on every machine but generally we find they work well where a combined regulator rectifier is fitted and on many British Bikes. They do not work when there is a separate rectifier and voltage regulator, on field controlled alternators (those with brush gear or a fixed field winding) or basic Japanese 6 volt systems that supply the headlight with AC power, again these systems will have separate regulator and rectifier. They must not be used with bikes with ABS or fuel injection.

FAQs 1. Is this item suitable for my standard XS250/360/400/650/750/850? No. The XS range had a field controlled type generator which must have a battery fitted for the generator to work 2. Is this suitable for my Royal Enfield? Models with standard points ignition: Yes, models with factory fitted or after market electronic ignition: Maybe. Models with EFI: No - must not be fitted to these machines. 3. Will this work on my 6 volt Yamaha XT250/500, Honda C50/70/90, CG125 or ©All rights reserved. Rev 2 Oct 2016

Our best selling battery eliminator kit. Order number: BE1

Battery Eliminators DAX? No, these 6 volt systems have separate rectifiers and regulators and are too basic to run an eliminator. They used the battery to soak up excess power and experience has shown that battery eliminators cause problems and fail in a very short time on these systems. 6 volt machines converted to 12 volts using a combined regulator rectifier usually run fine with a battery eliminator. 5. Will there be any issues with the MOT? No. The tester will have to start the machine to check the lights, make sure they are aware of this. The MOT test guide tells the tester that not all motorcycles have batteries therefore the engine should be started to test the lights if no battery is fitted. 6. Will my lights works normally? Yes but lights may be dim and indicators may not flash at idle. Once engine is above idle lights will be bright. This will be the same with ALL eliminators - because eliminators cannot produce power like a battery does. 7. Can I fit this as well as the battery? No. Its not advisable as the eliminator may hold up the voltage and fool the regulator that the battery is charged when in fact it may be flat. 8. Will this work if my bike has a power valve? Yes. When you start the engine the valve will cycle and run normally. This mod is extremely popular on track bikes as a battery eliminator is lighter than any lithium battery, maintenance free and doesn’t go flat when not used. 9. Will this improve the spark/ignition/charging performance? No. In no way can ANY battery eliminator improve the ignition or charging system. An eliminator is a maintenance free way to reduce weight and increase safety. 10. Will my electric start work? No. Eliminators do not supply any power so cannot power an electric start.

©All rights reserved. Rev 2 Oct 2016