capacitor size

28 replies to this topic
  • geoffro

Posted October 18, 2007 - 01:21 PM


Can any electrical boffins help with the type of capacitor needed for battery removal.(dont know what thats measured in,volts amps ohms etc).
We dont have battery eliminator kits in South Africa.Oh and have done searches on the forum.......thanks

  • bandit99

Posted October 18, 2007 - 02:10 PM


If you use a flux-capacitor you can travel through time :crazy: :D

  • tweav

Posted October 18, 2007 - 02:37 PM


I would try a 12volt rated 1/4 farad cap it may even still crank it.

  • CORider63

Posted October 18, 2007 - 09:00 PM


Make sure you get a capacitor with a voltage rating ABOVE the output of the bike. Keep in mind that a standard 12V battery is comprised of six 2.2 volt cells for a total of 13.2 volts. In order for the bike to charge the battery, it needs to to have a higher voltage than the battery. I wouldn't go less than 18 volts.

Exceeding the rated voltage of a capacitor can turn it into an impressive firecracker. :crazy:

  • tweav

Posted October 18, 2007 - 10:52 PM


the problem I see with using a 18 volt cap is , that the voltage regulator will be running wide open and will most likely run mid 16 volts unsurpressed . I'm thinking that at 16 volts connsant running ,you can kiss your ignition box goodbye. I'm thinking that a 12 volt rated cap will do 14 + feedback on the regulator like a battery and shut it down there .I know a 12 volt 1/4 farad cap will hold 14.7 because I have one in my truck doing just that ,for 3 years now . kind of off topic but , What is wrong with having a battery anyway???????

  • geoffro

Posted October 18, 2007 - 11:09 PM


I want to do the whole weight reduction thing throughout the bike.And NO i didnt want a YZ,just a lighter WR(do a bit of MX as well)
AND yes I am also working on the gut as well....
thanks for info guys

  • Thumper_Bloke

Posted October 19, 2007 - 12:07 AM


No, just remove the battery. Why use a cap? You'll probably be ditching the lights and starter too? Then remove it all. Just leave the V-reg and original ignition.

COrider63 is right about the voltage. The voltage of Capacitors is the working voltage (WV). The WV for this application would be at least 25. There are 16wv caps available, but i wouldn't use it. The WV of the cap will not regulate or "supress" anything. The v-reg will still keep it below 14v.

Oh, and i bet our stock DC-CDI ignitions will live beyond 16V, probably past 20v, but it would be rather expensive to test this.

One last thing to mention: our voltage regulators are shunt type. So, the more they have to shunt, the hotter they get. In other words, if the stator voltage isn't being consumed by lights or the 12v SLA battery, then regulator will get hot and may shorten its lifespan.

  • geoffro

Posted October 19, 2007 - 10:09 AM


wow thumperbloke you obviously a informed electrical guy,thanks.Are you saying its a bad idea to run without battery even if lights etc are off(cap or no cap)?

  • AnthonyB

Posted October 19, 2007 - 10:28 AM


Just put in a smaller battery ... it'll be lighter than a capacitor and be done with the problem. :D
You're in South Africa ... Contact Startline as they're probably the most reasonable :crazy:

  • Thumper_Bloke

Posted October 19, 2007 - 12:46 PM


Are you going to use the bike on the track? Or are you going to ride 100 miles into the bush? The factory 12v charging system is a complete SYSTEM. It is designed for longest life of the components. Removing any item would be bad. I am not saying it won't work. Many people run without the battery. I'm just saying its not designed to have components removed.

We need "WR-battery-less" forum members to reply to this post.

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  • geoffro

Posted October 19, 2007 - 01:14 PM


I race mx "socially" in the novice class, and ride socially in the bush.If I am going to risk reliability with electrical items then I'll have to just suffer the extra weight on the track and start eating even more salads!

  • tweav

Posted October 19, 2007 - 03:03 PM


you can safely take the lights of the later model wr's they are on a differant set of coils then the battery . the other thing you could do is swap out the box and coil for the yz units . then rewire your bike to bypass the reglator . this would be like a yz setup up but you'd still have a lighting coil

  • ncmountainman

Posted October 20, 2007 - 07:55 PM


my 04 wr450 has been running for more than 2 yrs without battery,lights,ign switch,splitter switch etc. although i don't own the bike any more my buddy does and i see it regularly,i don't know if this has any bearing on why it works but i grounded the neg lead to the frame at the regulator;which has never gotten hot:excuseme:

  • AnthonyB

Posted October 23, 2007 - 04:46 AM


Why not eat salad for the next week and replace the keg /your belly for a 6 pack as against losing your E-start functionality? :crazy: .... besides which .... the weight saving is minimal in the greater scheme of things :D

As you're South African, you'll appreciate the analogy of our "friends" in the Cape removing their front teeth ... for what exactly?

  • geoffro

Posted October 24, 2007 - 05:50 AM


well even if I'm ripped like an athlete, I'm still lugging an extra 12kg of WR around an MX track which my competition isn't!!
our friends in the Cape have their teeth removed from fights and have no monet to replace them:bonk:

  • ncmountainman

Posted October 24, 2007 - 06:59 AM


Why not eat salad for the next week and replace the keg /your belly for a 6 pack as against losing your E-start functionality? :crazy: .... besides which .... the weight saving is minimal in the greater scheme of things :D

As you're South African, you'll appreciate the analogy of our "friends" in the Cape removing their front teeth ... for what exactly?

gee i wonder why those twig jockeys like carmichael and stewart spend so much money and time lightening their bikes.....oh, could it be that no matter what you weigh a lighter bike will handle better:thinking:

  • geoffro

Posted October 24, 2007 - 02:41 PM


thanks NC ,good to know some guys are technically minded!!

  • AnthonyB

Posted October 25, 2007 - 05:10 AM


Remembering your original question, which was the replacement of your battery with a capacitor, (which incidentally won't shave much weight, once you've exchanged one for the other), furthermore, that all batteries have what is termed internal resistance", which the design of the regulator takes into account, meaning that you'd have to install some form of shunt across the cap, should you decide to go that route. :bonk:

I'm not disputing a lighter bike handling better, I'm debating the merits, (usefulness, costs and performance), and the saving, or should I say removal of some +-100 grams, (assuming the use of a good zinc-air battery against your current lead acid one) ... in my opinion ... it isn't worth it. :crazy:
I acknowledge I've done it all and some, however given the benefits vs. time & costs and the advantage of hindsight ... hmmmmm ... :applause:

If however time and money aren't an issue, and you want the edge for whatever reason/s ... then strip the motor, overbore it, replace cam(s), (and/or profile the rocker arms), lighten, nitride, (&/or shot preen as appropriate), and then balance all reciprocating parts. Reshape the combustion chamber port the head, then coat it along with your lightened piston . Replace the carb. Change the ignition mapping and gearing. Replace the exhaust in it's entirety. Rebuild the airbox for a larger filter. Replace the shocks and carve the seat for starters ... :D
PM me and I'll gladly give you the info / engineering shops I've dealt with in SA.

For the record ... Our "Cape friends" do it for aesthetic reasons!

  • Thumper_Bloke

Posted October 25, 2007 - 07:31 AM


Is this a power-to-weight issue or a weight-to-handling problem?
I think he's looking to lighten the bike to make it handle better?

  • geoffro

Posted October 25, 2007 - 07:51 AM


If thumperbloke can understand the question,why cant you anthony B!!
I did not want a faster bike just a +-5 or 8 kgs lighter bike.Lighter bikes corner better in thick sand,dont make you as tired(no matter how big you are),less sprung weight.....should I go on.I've been riding bush and mx bikes for 25 years ,I KNOW WHAT I WANT!!!!!
If you are so bored and looking for an argument find another thread to waste their time please.
For all you other guys with genuine advice thanks alot!


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