I have an older (1998) Harley Electra-Glide that my son upgraded with an aftermarket stereo. Its a nice JVC unit, but there's one problem with it...

Apparently this unit requires both switched and constant +12v connections. Leaving it parked for a couple weeks without a battery charger attached resulted in a dead battery. Connecting the constant +12v lead to a switched source eliminated the parasitic drain but causes the unit to revert to standby mode after each turn of the key.

So I was grousing about this at a gas stop on Sunday, and a fellow on the other side of the pump suggested that I wire a capacitor into the constant +12v lead. He said it would charge up the first time I started the bike, and carry the load for the rest of the day's ride. Maybe not for two weeks worth of sitting, but certainly a day's worth.
Unfortunately, I could not track down this helpful rider at the conclusion of the run, and no further details were forthcoming.
Using a capacitor as a substitute for a battery is outside my level of experience. Can any of the Forum tinkerers offer advice?
Thanks in advance!

If it's draining the battery, I'd expect it to also drain a capacitor (but I do not know that for a fact).

Perhaps a higher capacity battery, or the trickle charger.

In my motorcycling days a motorcycle battery didn't have much capacity, and every time it was discharged dead, it got weaker.

Trickle charger

I'm a bit surprised the constant 12v lead would drain the battery that fast. That constant 12v usually has a very small power draw. I have an aftermarket stereo in my truck and after setting for a month some time back, the truck fired right up without any signs of a dead battery.

BigSwede's trickle charger suggestion is likely your best alternative.

quote:

Originally posted by bigdeal:
I'm a bit surprised the constant 12v lead would drain the battery that fast. That constant 12v usually has a very small power draw. I have an aftermarket stereo in my truck and after setting for a month some time back, the truck fired right up without any signs of a dead battery.

BigSwede's trickle charger suggestion is likely your best alternative.

This too, I suspect you have another drain. That constant power should only be powering the clock and pre-sets, very little power usage

Well, there doesn't seem to be a whole lot else that could be causing the parasitic draw.

I do know that once he rewired that lead from constant to switched, the dead battery problem went away.

I don't lose the presets; they seem to be stored in NV memory. I do lose the clock, the mode (defaults to standby) and the last tuned station. In FM, it defaults to a factory default frequency, not a preset. Where I live, that frequency is unfortunately a station that seems to exclusively play Guatemalan gansta rap. Not my cup of tea.

I do use a trickle charger, but that's an inelegant solution, and impractical on the road. I'm getting close to retirement, and one of my bucket list items is to tour the US on my H-D. Would prefer not to have to plug in everywhere I go if I end up staying more than a couple of days.
First world problems, I know.

Battery is the biggest one I can fit into the compartment. New as of Sep 2018. I suppose that I could get a small second battery and an isolator, and stash them somewhere in the fairing or the tour pack, but again that isn't clean. And as noted, every time a battery runs all the way down, it loses capacity.

I fully expect that the capacitor would drain; don't really care as long as it took more than 18 hrs to do so.
Benefits of a capacitor vs battery in this situation seem to be:
long life: up to 8 million cycles
High Power density
Low ESR: can be used as a rechargeable battery and ideal for back up purposes
Quick charge: charging 10 seconds to 10 minutes to reach its rated capacity of more than 95%.

(Thanks, google).

Maybe more to the issue. I’d have the entire stereo wiring checked over.

Unless I misunderstand, which is possible, i'm short on caffeine today, you're radio is like 99% of all the other radios out there - it needs 12V constant for power & 12V switched to know what the vehicle is doing & what it should do.
run a 2nd wire. Don't fuck around with caps (won't work well) and don't add a 2nd battery. An 18ga wire from wherever you can find switched 12V will be the easiest, simplest and as a bonus, will actually work.
Its a motorcycle, it can't be that far of a run. a 'vampire' on a wire or find a switched fuse & use an 'add-a-circuit' type connector. I'd bet there's a 12V-switched wire on the back of the radio just waiting to have a butt splice added to it.

Did I mention i'm short on caffeine today?

The radio may very well be your problem, but I'm betting you have a short or something there that is drawing way more power in standby than it should. Could also have a dead cell in the battery that can start it fresh, but can't turn it over if it's not 100%.

Pretty much every radio in every vehicle requires constant 12V power. The Factory unit probably did. The parasitic draw from the memory functions really shouldn't draw that much power.

Test the battery
Pop out the fuse to the radio next time it is to sit a while and see if the problem goes away or not.

I put an interrupter in line with my dash cam, it came with the hardwire kit, it cuts power to the cam if the battery voltage drops to a selectable level... leaving enough power to start the car. Something like that might work.

check all the circuits for an electric drain, the battery should be able to keep up with the small draw.

Buy a Battery Tender, based in FL, Deltron is the company, you can buy direct, Amazon, most motorcycle stores. HD sells their branded unit, and it looks to be made by Deltron.

It comes with a harness you attach to the battery and then a simple quick connect/disconnect. Plug it in when you are not riding to maintain the charge.

If you are on a ride the bikes charging system should be able to keep up.

https://www.batterytender.com/

Like mentioned above you need to actually measure the parasitic draw to know for sure.
Maybe it is something else or maybe another device/radio would draw less.
A switched radio shouldn't draw so much as to kill a battery.

^^^^^^ What he said.

Need to first determine what the draw really is. This is the most important information, since this will be the basis from which to start. Next, charge the battery and have it properly load tested, have to make sure the battery is good. Otherwise you are chasing your tail.

Make sure the switched power is actually there and the radio is seeing it. If that is all good and you have a substantial draw that goes away when the main power is removed from the radio, then the obvious is clear, the main radio is the issue. Could be that it is simply not shutting all of the way down when the switched power is removed. Repair it if you can or replace it.

This really only leaves you with a few choices,
1. Keep hooking a battery tender to the battery to keep it up.
2. Hook the main power to a switched power source and deal with the consequences of that, or.
3. Replace the radio.

Bikes have limited space and I dont see you having room for a capacitor. I think that "solution" is not the best one in this case.