USCA Sidecar Forum

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`Aux. Battery?

For what it is worth, some Mercedes and some BMW's had the battery in the trunk. The battery had a fitting on the end that a piece of clear tubing goes to and then vent to the outside. I know that Interstate had such a battery the the model number started with MB. Should work in sidecar trunks as well as it did in car trunks.

#4AWG cable is serious overkill. #8 is more than adequate, really #10 would do, and a fraction of the cost, easier to route [because it is at least sort of flexible] and lighter. If you do go for big cable, I suggest you consider using something like https://www.grainger.com/product/ANDERSON-POWER-PRODUCTS-Power-Connector-3BY22?s_pp=false&picUrl=//static.grainger.com/rp/s/is/image/Grainger/3BY22_AS01?$smthumb$. These connectors are used to charge electric fork lifts and make a clean and easy to use connector from the sidecar power supply to the bike. They come in many wire sizes. I used a plexiglas plate under the seat to replace the battery as a place to connect all the bike power. The connectors on that plate are attached to the cable coming from the sidecar with this sort of connector. Over 10 years with that set up and no issues ever.

Decided to go with #10 wire and the Anderson connector per your advice. Combined with the Odyssey 925, it should last forever. Thanks for the assistance.

Ray Paige
Bitterroot Valley, MT

Remember when I said "If you go with big cable..."? I don't think you'll find an Anderson style connector for #10 wire. To be sure, there are suitable connectors out there, just not like the Anderson product from Grainger. Anderson makes a smaller "Powerpole" range that is available from other sources. I'd go to McMaster Carr and check out what they have available or if you have a local Grainger, walk in and ask for help.

Also, #10 will doubtless do the job but I always try to use things that are a bit oversize. Check to see what the output of your alternator is, size the wire for that plus a safety margin. I believe you'll still go with #10 but since I don't know the output of your alternator, it's better to check.

Al, you are right. I'll have to use Anderson Power Pole connectors. No local stores, so I'll have to order. The Wing is over in Idaho, so I'll have to wait until I get it home and run diagnostics on the alternator (probably still be #10 or at the most #8 wire). Anyway, I'm now headed in the right direction! Thanks again.

Ray Paige
Bitterroot Valley, MT

Guys, it's not just about charging capacity of the alternator and running accessories on a bike as far as wire sizing! The biggest amp draw is the starter (as much as five times what the alternator puts out!), and you had better provide enough for it, even at the short lengths of cable on our bikes. If you don't, you will create a serious voltage drop that can/will affect the ignition circuit which can/will make a difference in how easily the engine will fire while cranking. Once the voltage drops below a certain amount (usually around 9.5 volts), most ignition circuits will not fire the coils, or at the most will give a weak spark.
Without doing an actual amp-load test to determine the draw of your particular bike, I certainly would at least watch the voltage at the battery with a meter as you crank the engine.
Are you going to go with a smaller size just to save a couple of bucks? Not me! I want my bikes to have all the power they need with minimal voltage drop, especially during cold starts. I would use only fine-strand #8 or #6. I do agree that #4 might be a bit overkill, because that is what most cars use for the ground.

Al, thanks for the heads up on the Anderson brand of connectors. I used to use them to connect my batteries in my boat, but never knew the brand name. Just got them at the local marine supply.
I did google the brand and found another great site to get all of Anderson's products, and they do offer a Powerpole series that goes down to #10. The prices are about 1/3 of Grainger's, too. Lots of body color choices as well.
https://powerwerx.com/anderson-sb-connectors-sb50-50amp
This site also has a good size selector calculator, but not many bike manuals give the amp draw of the starter, so it's a shot in the dark. However, they do say that Anderson connectors are good for many times their rated amperage in short bursts.
FWIW, most small auto engines draw about 250-350amps during cranking, with larger V8's drawing around 600-700 amps. I would estimate that a 1500cc engine might draw 180-200 amps during cranking, and according to Anderson, their #8 will handle 50 amps continuous, and their #6 will handle 120amps continuous. #8 would probably be OK for short bursts at around 150 amps, but #10 (good for 30amps) is pushing the limits of even short burst capacity.
My Kawasaki Voyager has two alternators that put out a combined amperage of 55 amps, and I wouldn't use anything less than the #6 cable/connectors, even though the #8 would likely be fine for running everything else except the starter. My original ground wire from the battery is a #6, so taking into account the extra length of the cables from the sidecar trunk, #6 would be the minimum size I would use. If a bike has 1000cc or less, #8 might be fine.
BTW, Al, I do like your idea of setting up a connection terminal using the plexiglass insulator. It gives me ideas! Thanks!