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Could I connect a capacitor in paralell to the battery?

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jeffyjeff
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Joined: 02 May 2020
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PostPosted: 22:41 - 01 Feb 2023    Post subject: Reply with quote
stinkwheel wrote:
...What I haven't checked is if a near totally flat battery will immediately pull down any current generated by a kick preventing it starting. A knowledgeable friend has suggested if this was to happen, connecting a power resistor in the battery positive should allow the cap to charge first but still allow some charge to get into the battery once running.

It seems to me that a discharged capacitor would be a more likely current path than a flat battery. Perhaps further experimentation is in order. Like maybe connecting the circuit as described and attempting to start the engine on a flat battery (with and without the resistor). Then you will know for sure how the system will react to your modification.
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 23:34 - 01 Feb 2023    Post subject: Reply with quote
Aye. Don't have a flat battery just now and I don't want to deliberately flatten one.
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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jeffyjeff
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PostPosted: 02:41 - 02 Feb 2023    Post subject: Reply with quote
fair enough. I would not willingly flatten a serviceable battery either, unless I had one that was getting on in years.
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A100man
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Joined: 19 Aug 2013
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PostPosted: 09:44 - 02 Feb 2023    Post subject: Reply with quote
jeffyjeff wrote:

It seems to me that a discharged capacitor would be a more likely current path than a flat battery.


Yes far lower internal resistance/impedance..
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mattsprattuk
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Joined: 12 Mar 2007
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PostPosted: 11:24 - 02 Feb 2023    Post subject: Reply with quote
Voltage Sensitive Relay.

It only triggers after detecting a charging voltage for a few seconds, ie: when it's running.
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Kickstart wrote: Hi I tend to agree with Matt. All the best Keith
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stinkwheel
Bovine Proctologist



Joined: 12 Jul 2004
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PostPosted: 18:31 - 05 Feb 2023    Post subject: Reply with quote
Well, I did it again, left the ignition on on my other bullet while I was sat chatting and drinking tea with a mate. It had just enough juice left in it to start and idle but if I increased the revs above idle, it would die. I had a very slow ride home at under 10mph and coasting down hills (thankful for trials gearing which will pull at idle or I'd have had to call for a lift).

Good opportunity to try the capacitor with a flat battery though. Measured 8.5V on the battery, dropping to 4.5V when the points closed which was only just enough to get an idle but immediately died if you increased the revs (presumably the flat battery taking any alternator output leaving nothing for the coil). Fitted a capacitor and after a couple of stutters, it fired up properly and revved normally showing 12.8v in the loom.

Seems like I can safely leave the capacitor in there all the time and it should start on a flat battery. If it doesn't, disconnecting the battery will get me home. The lights will work on this bike too because they are AC on a different phase. It probably doesn't really need a battery at all.
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I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.
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