Aux battery install

Main potential problem [pun] I'd see is a possible sparking or arcing at switch. If fuel is stored in or near chair or near switch that's something to consider. Could be a whole lot of amps in a deep cycle depending on what you choose.

This is basically not a good idea as stated. Putting two, very dissimilar in chemistry and capacity, batteries in parallel is a recipe for premature battery failure.

Installing a 'make before break' battery selector switch could accomplish what you are looking for. Normally, the tug would run from it's own battery, when you want to go to the 'reserve' battery, the tug's battery will be switched out of line. The 'make before break' is for those unfortunate, but Murphy says inevitable, times when you have the engine running and switch from battery to another.

These types of switches are commonplace on boats (and NOT inexpensive!), so you can source them from any marine swindlery (chandlery).

A high current breaker or fuse would also be a good idea as close as possible to the deep-discharge battery, and a second, lower current fuse/breaker to the feed to the tug. Remember, an over-current circuit protector isn't to protect the device at the end of the circuit, but to protect the circuit from the device. It would be a very bad day if one (or more) of the thin wires on tug goes overcurrent and melts everything down.

Just sayin' 🙂

Excellent info from MichaelH!

I'm planning on a battery in my sidecar when built but not actually 'Auxiliary'. In general there's no good reason to run 2 batteries. Even for camping a single large capacity battery can provide a whole bunch of juice. Might as well remove bike battery entirely and simply use a deep capacity battery mounted in the car, using #2 welding cable to connect to main circuits on bike.

Note that most 'Deep Cycle' batteries are not designed for continuous short cycles of charge/discharge and it will actually cause premature failure. It's better to let them run way down then do a longer recharge because it's the number of discharge/recharge cycles that kill them. Better to use a Marine battery with lots of reserve cranking amps for all battery needs in the sidecar outfit.

One other option is to install a new motorcycle battery and the sidecar battery but not connect the cycle battery. Then if you accidently discharge sidecar battery so that it won't even crank the bike, you can temporarily hook up the fresh bike battery for that emergency starting use, after disconnecting the dead battery from circuits, then disconnect bike battery and reconnect sidecar battery to recharge. As Michael mentioned there are special switches made for just this sort of installation.

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So what you are saying is to use a Battery isolator device bewteen the 2 batteries?

Charge the aux battery from bike's alternator using Shottky diode. This will save your big battery from short discharges, that it's not designed for.

In home, charge aux batt from mains using normal AC charger. Use energy from aux battery, and if not "deeper" discharged, don't connect it to bike. Don't use expensive switches. Just simple, high-current connector. And you must know how big current you will use. Few amps? 10A is really big current when you don't use big bulbs. Typical camping fridge consumes 4-5A and it's probably the biggest consumer for your aux batt. I believe you will be using LED light for camping and small (few watts each) bulbs in car. Laptop, mobile phone chargers plus fridge and some light shouldn't exceed 10 amps. So you don't have to use expensive connectors and switches. You can get apropriate connectors for about $1 each (or few bucks. Just think when connecting anything. For any external battery and other "battery games" I use the simpliest and most robust connectors I know - so called Crocodile Clamps in 2 colors, for "-" and "+".

Gasoline, battery chemistry and high-amp electricity? There is very basic rule for any potentially dangerous equipment: Don't know how it works? Don't use it! This is one of most important life sentences that I learned in school. Read, learn and then use. You will be surprised how trivial it is.

For the next project (external alternator from other vechicle) I consider switching to 24V installation (alternator from small truck). Lower currents and higher available power for street-legal main bulbs (75W@24V vs 55W@12V). And use of any truck-equipment is mush easier. Good, cheap street-legal rear LED lamps for trucks are available few times cheaper than 12V ones. Any DC/DC converter (eg. for laptops that require more than 12V) is much more effective and easier to build in step-down mode (eg. "24V" to 19V) than step-up ("12V" to 19V). Cables in 24V installation have mush less influence on bulbs light intensity than in 12V installation. Hardcore but why not to try in your bike? 🙂

Txart - 3/26/2013 1:13 PM

So what you are saying is to use a Battery isolator device bewteen the 2 batteries?

Well, you could use an isolator but I wouldn't. I'd simply wire everything to the one big fat battery in the sidecar and run off that. You could install or carry an accurate voltage gauge to monitor condition. If you run AC keep a close eye on it, otherwise not much to worry about.

And then if the worst should happen and you somehow discharge the biggy too far, just use the Marine switch to use the small motorcyle battery to start the bike. Let it run a couple of minutes to restore the surface charge, then switch back to your main battery.

Don't know what your design is but mine includes a 6 gallon fuel cell in the hack body. One I have is out of a friend's race car so it's especially safe, well sealed and externally vented. Regardless, I'll build a complete wall, a cubicle around it, that's completely sealed to keep vapors from entering rest of tub and presence of battery. Same for battery, an airtight compartment vented to exterior. Maybe not necessary but, ya know? Also some redundant tie-down or clamping to really hold that chair battery immovable even in a tip over, God forbid.

Yes, another thought is to use an isolator just like in an RV, with identical wiring setup. Only use auxiliary battery to run your A/C unit or camp equipment, and only use bike batttery to run all the bike stuff, completely isolated one from another. Should work fine. However it is still important if you use a genuine Deep Cycle battery [which I don't suggest] that you let it run way down to almost complete discharge before recharging. Do a search on 'Deep cycle battery charging' and similar, they don't last long at all if run on short cycle of charge/discharge/charge like a normal wet cell battery. The Deep cycle' part is that it will withstand very deep discharge with no damage.

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