Who needs a battery anyway?

Having built my “under-seat” tray to hold the CDI and SAPC units, all that was left to do, was to place the battery somewhere.  Part of the problem of owning a track bike, is that it is unlikely to see regular enough usage to keep a standard battery charged.  Standard lead-acid batteries are heavy too.  If you are used to seeing a car battery, motorcycle batteries do look miniature by comparison, but my new tray did not allow room for the standard RGV battery.

The VJ21 and VJ22 model RGVs were fitted with a kick-start system.  Given that there is no electric start on this bike and that is devoid of lights and indicators, the only real function of the battery is to power the CDI and SAPC units and spark plug coils.  Like most engines, an “electrical generator” of sorts uses the spinning of the crankshaft to recharge the battery.

Some racing bikes run a total-loss system.  The charging system causes a drag on the engine.  The more current you try and draw from it, the more the drag and the bigger the performance hit will be on the engine.  A total-loss system will not recharge your battery as the engine runs. By doing so, less load is put on the engine, leaving more power to actually propel the bike.  Unless you are at the elite level of the sport, it is unlikely that having a total-loss electrical system is worth the trouble of recharging the battery after every race.

Given that the generator provides electrical power, the battery becomes superfluous to requirements. The regulator/rectifier and AC generator of the RGV is sufficient to power the electrics of the bike while it is running, and your leg (and kick-start) is enough to provide the initial power to start the bike.  A “battery eliminator” can be built and substituted for the regular battery, saving weight, space and the “oh-no” moment, caused by a battery that has gone flat through lack of use.
Although commercially available “battery eliminators” can be purchased, “Mick” on the currently out of action Yamaha-rd forum  wrote a succinct post on how to build one:

You need;
3 x 4700µF 25V electrolytic capacitors
1 x 500ohm resistor
some solder
a soldering iron
source of power for the soldering iron
cup of tea
decent music

OK, solder all of the components together in parallel; that is +ve terminal to +ve terminal. This is important. The resistor can go in any way round, but they must all be connected in parallel with each other.

Remove the battery from your bike.
Connect the eliminator up the right way round (+ve end to +ve connection on the loom)
Switch the bike on (note: the PVs won’t move until the engine’s running)
Start ‘er up.
Ride the bike, and enjoy the feeling of having lost 2.5kg of ugly fat.


How hard could it be?  There was a discrepancy between the commercially available, and Mick’s battery eliminator.  Mick suggested a total of 14100 micro-farads, whilst the Zeeltronic schematic had 30000 micro-farads. (and a different amount of resistance).  From my limited understanding, the capacitance allows a good way to smooth out the voltage provided across the unit, whilst the resistance provides the regulator/rectifier with a workload.  Without this load, the regulator/rectifier would overheat.  (Feel free to correct me here)

Battery Eliminator PartsI bought the components from Futurlec.  Shortly after I ordered the parts, I read the horror stories from “customer review” websites.  Put simply, they grossly understate shipping times and I am not convinced they ship your order when they claim to.  They also allow normal mail shipping of their products and hence they cannot be tracked on-line.  This further reduced the transparency of their operation.  The parts did arrive after four weeks.  Their website made me believe it should have only taken two…  In days before Internet shopping and on-line tracking of parcels, I would not have thought twice about the length of time it took for my order to arrive.  These days though, it is a different story.

Once I knew how large the capacitors were, I purchased some cabling and a zippy box of sufficient size from the local Dick Smith Electronics shop.  Then all I was missing was the cup of tea and some decent music!

Battery Eliminator Circuit BoardRather than use a breadboard, I drilled holes in a piece of Perspex to hold the wiring in place and rubber mounted the board inside the zippy-box in an attempt to shield the components from solder loosening vibrations.  Once I had finished construction and fitted it to the bike, I tried to start the bike… At 30,000 micro-farads, I could not generate a spark.  In the end, I removed one of the capacitors (reducing the overall capacitance to 20,000 µF) and had instant success!  (Yay!)

Given that my de-soldering technique is even rougher than my soldering technique, I didn’t bother providing photographs of the final product.
For those of you tempted to try building your own battery eliminator, I have ended up with the following configuration:

  • 2 x 10,000 µF 25V electrolytic capacitors
  • 1 x 1000ohm resistor (5W)

So now you have three different sets of figures to guess at!  Good luck!

Battery Eliminator wired up.Battery Eliminator in boxBattery Eliminator vs. Battery
(Edit: Pictures added)

3 thoughts on “Who needs a battery anyway?”

  1. Thanks for posting this!

    Why do you think the 30,000 micro fared capacitance created a no-spark situation for you? Were the capacitors pulling too much energy from the system on cold start?

    Looking at the link you posted for the commercially available battery eliminator kits… the schematic that they provide on there shows 1k Ohms for resistance and 30000 to 45000 micro fared for total capacitance. Do you think the higher resistance would have allowed the higher capacitance to work as desired?

  2. Hi Ben,
    Thanks for the comments.
    As you suggested, I think too much energy was being taken for a cold start. Each kick (on my RGV at least) doesn’t result in much turning of the crankshaft so that doesn’t help…

    As for the bigger resistance helping – I honestly don’t know, but given that the resistor is in parallel it makes sense that raising the resistance would force more current through the capacitors. So what you are suggesting makes sense and is probably correct.

    I built this some years ago. When I went back and re-read my post, I see that I did end up with a 1K Ohm resistor (not the 500 Ohm) I’m not sure if raising the resistance further is a good idea. I don’t understand the charging circuit well enough to know whether this would cause problems.

    If you – or anybody, reads this with the intention of building their own, just make sure the resistor you get can cope with the power that you will be putting across it. I can’t remember how I came to the conclusion to use the 5W one, but it had something to do with Ohm’s Law!

  3. Can anyone tell me what the resistor does. I’ve ordered 2 x 10,000Mf capacitors which arrived today. I put them on my CB125 system and tried them. This is impatient, as the resistor hasn’t arrived yet. The bike ran at low revs. The points were arcing like mad, and the engine misfired badly and would not rev any higher. Is this because the resistor is not fitted, or because of some other problem? i.e. bad points condenser?

Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>