Battery less approach with full wave rectifier

[fatcaaat]

Hi all, wondering if anyone has an idea on how to pull this approach off. I'm trying to use up parts I have in the garage to build a custom bike without trying to invest additional funds to complete it. To that end, this particular bike will likely be one that's not ridden too much, and I would prefer to see if I can build without using a battery.

For the electric, I'm using a TRX90 stator that I wrapped for lighting as full-wave, so I was wondering if anyone had some thoughts on how to run this without a battery. I'll obviously need the full wave rectifier, which I have one, and I"ll need a voltage regulator as well...think i have one. But I've never seen full wave be done without a battery. What about a capacitor? I have an old capacitor from a Norton Commando laying here that is designed to keep enough juice to get the bike started in case of a dead battery...would that work here?

 

[69ST]

This is over my head. I am aware of "battery eliminators" and those do use capacitors. IMHO, it's easy enough to swap a battery between bikes, at least if we're talking about CT70 or Z50 size machinery. I've done that since day one, seeing no advantage to watching unused batteries deteriorate.

 

[allenp42]

What about a capacitor? I have an old capacitor from a Norton Commando laying here that is designed to keep enough juice to get the bike started in case of a dead battery...would that work here?

It is possible. Ran across more than one article on this subject in the last few weeks, but I am by no means a subject matter expert. In general, the voltage rating will need to be at least 50% higher than the regulated voltage you target. Also, your lights will be dim at idle//low rpm. Regarding size, based on what I've seen used (physical size) it can't be more than about 500uf. Of course, bigger is better but if you're trying use what you have, then give it a shot. As long as it's large enough for the Rec/Reg to function properly, voltage rating is ~25v min., then it just becomes an issue of how much flicker you can tolerate at low speeds.

 

[fatcaaat]

Thanks for the input. The stator setup produces 65w DC power as measured. I did some testing of it on the bench with an engine. I did not loop in a battery to the testing, so you are right, it did dim at idle but just off idle the lights were plenty bright. It wasn't a super scientific test...i kept adding different and more bulbs until it couldn't keep up, and that was right around the 65w combination.

i had a pitbike that used a capacitor in it, but it was only used to keep the digital dash running and nothing more. Everything else was run off the AC line.

 

[allenp42]

II know you're trying to use what you have, but you may want to read about "Super Capacitors". Some people are buying them and making a "bank" of capacitors to replace the battery. I don't plan on trying it unless it just for the educational benefit. To me, as long as I can buy decent gel cells at $10 a pop, it makes the justification a little more difficult to drop $100 on capacitors.

 

[69ST]

There's one aspect of capacitors that leaves me feeling a bit uneasy, they can discharge instantly. 500uF is a lot of electrical energy to stuff into the confines of a bike, especially a small bike. The constantly changing, heavy, vibrations are a harsh environment for electrical componentry. If a condenser of this size were to fail, I see a high probability for serious damage. There's no place for the lighting discharge to go that's more than a few inches away from the rider, or fuel. For that reason, I agree with Ray that AGM batteries are cheap and have proven reliable. FWIW, I've only had to replace one since 2004...that was back in 2018. Can't think of many items that deliver that kind of service life. Dunno if the newer batteries will last as long, or if that first specimen was a freak. I would suggest taking declining product quality into consideration...like all of the ignition capacitor failures we've seen posted here, in just the last 4 years or so. Sometimes it's easy to get over-focused on trying to realize a concept...to the point of losing sight of practicality. I say this not as a critic, but as someone who has done this many times.

 

[fatcaaat]

Actually, Bob, I think i'm going to agree with your assessment. Even if I don't want to invest in a permanent battery for this bike, i can just go ahead and steal a battery when I intend on riding it. That's obviously the cheapest way forward and probably the most practical.

However...here's the but....

Is it possible to just reconfigure the wiring to make this AC then? It is wrapped as a full wave setup on the coils...one continuous length of wire wrapped across 4 prongs of a TRX90 stator plate. Could I not just ground one end of it and have a single AC line of juice coming out? Since there is about a 5% loss of power for full wave from AC, this means I could have as much as 70W of AC power on a single line. IN this case, all I would need is a 12v regulator and tie into that to run my lighting (as long as I use bulbs that require AC and don't need any DC power). I wonder if that could technically work? I'm going to wire this bike completely from scratch outside of the CDI/Engine subharness I have sitting here.

 

[69ST]

I agree with your understanding of doing an AC conversion. Should work like a healthier version of the stock setup and 70W really isn't much current, IOW, I can't see much (if any) risk of smoking anything. If it fails, you should know soon enough and in drama-free fashion. Be careful though, my electrical knowledge has too many gaps when it comes to the fundamentals of engineering a system. That's why, for the most part, I go for the "tried & true" electrical solution(s)...too many other interests and not enough time to learn everything.

 

[allenp42]

IN this case, all I would need is a 12v regulator and tie into that to run my lighting (as long as I use bulbs that require AC and don't need any DC power).

In your case, that should work just fine as long as the 12v ac regulator can handle it. I'm pretty sure that trail tech (and others) has one but don't know how much that puppy can shunt.

 

[allenp42]

Took a look at the instructions for the Trail Tech 12v ac regulator. Bet it will work just fine and may save you some trial and error.

 

[fatcaaat]

I have one of the dratv high wattage ones...i think it's good for 75w which would put it at the top end of range. I might try that one first and if I have issues, i'll consider a trail tech. However, I think i'm going to actually wire it for DC and full wave and do a battery swap when i want to ride it. That might be the best way forward.

 

[69ST]

I have one of the dratv high wattage ones...i think it's good for 75w which would put it at the top end of range. I might try that one first and if I have issues, i'll consider a trail tech. However, I think i'm going to actually wire it for DC and full wave and do a battery swap when i want to ride it. That might be the best way forward.

The TT unit is rated for 150W and for the price seems like a decent value, imho. FWIW, the one on my red bike has seen something like 5000 miles of use; not the be-all-end-all of testing but, that's well in excess of 120 hours of real-world operation...better than going in blind.