Electric Bikes - 3 batteries

I've got a electric bike with a 24 volt system which is powered by two 12v deep cycle RV/marine batteries.

Obviously they're wired appropriately.

My question is can I add a 3rd battery to the mix by simply hooking it up to one of the original two?

Common sense tells me to hook it to one battery - positive to positive and negative to negative - thereby making the two of them the same as one ex-large 12v battery.

Exactly how would the connection be made?

Do you have a Currie e-bike (ezip or izip)? If so, you may not be able to mod it to 36V without a new controller (and throttle). In 2008, Currie changed the controller they use in their 24V systems. This new controller cannot power a 36V upgrade.

To add a third battery, you would want to wire the batteries in series. (Here's a brief overview of wiring in series or paralell. http://www.zbattery.com/Connecting-Batteries-in-Series-or-Parallel) Here's a link to an old thread on another forum about upgrading the Currie ezips--this was before Currie changed the controller that they used. http://www.ecoforumz.com/electric-bicycle-scooter/12475-36volt-cooling-mod-complete.htmlAlso, increasing the voltage on Currie systems requires cooling mods to minimize the risk of the motor burning out.

Good luck

I've got a electric bike with a 24 volt system which is powered by two 12v deep cycle RV/marine batteries.

Obviously they're wired appropriately.

My question is can I add a 3rd battery to the mix by simply hooking it up to one of the original two?

Common sense tells me to hook it to one battery - positive to positive and negative to negative - thereby making the two of them the same as one ex-large 12v battery.

Exactly how would the connection be made?

As near as I can tell from reading what your asking, it sounds like your talking about adding a battery in a FIG. 1 configuration, paralleling 2 - 12V batteries then going series with a third battery in that pack to stay at 24 volts. This won't get you any more distance or amphours as you're limited by the single 12V battery in the series.

Nwmtnbkr assumes you want to add a battery to make a 36V pack as in FIG. 2, in which case you'd have to do as he says.

"My question is can I add a 3rd battery to the mix by simply hooking it up to one of the original two"? I.e. the third battery would be wired to battery number one (or two) positive to positive - negative to negative. (To do otherwise would result in 36v if I understand).

I want to remain at 24v. So I can wire them up as I describe but I won't add any distance. Can you explain why?

hi with the 2 batts you have ie 2x 12v lets say they are 12ah. using 2in series would give you 24v 12ah. if you add a third batt after no 2 batt *** to *** neg to neg this would then give you 1batt at 12ah plus 1 double batt at 24ah. because the double pack is 24ah it would not get you any further because the 1st batt is still a 12ah so if would drain down your bigger batt. get 2x 20ah batts or wire in 2x new batts to the ones you have. hopeit makes sense ? regards rob.

I want to remain at 24v. So I can wire them up as I describe but I won't add any distance. Can you explain why?

CrimsonsnakeO is correct, but maybe hard to follow?

Three 12 volt - 12 amp/hour batteries can be wired three ways;

1) Parallel, giving you 12V and 36 amp/hours capacity.

2) Series, giving 36V and 12 amp/hours capacity. (Fig.2)

3) Parallel-series, giving you 24V and 12 amp/hour capacity. (Fig.1)

Your amp/hours are limited to the smallest/weakest battery in your series. If you had four 12V 12amp/hour batteries wired 2-parallel, 2-series, you would have 24V 24amp/hours of battery capacity, doubling what you have now. Adding one battery to your two doesn't improve things because the one 12V 12amp/hour battery in the series runs down in use at the same rate it always did, and then becomes a big resistor when dead, that you can't push the remaining juice in the parallel set through.

Hope this helps.

and then becomes a big resistor when dead, that you can't push the remaining juice in the parallel set through.

It's also quite possible you'll ruin the battery even before it starts behaving like a resistor.

If you're simply wanting to be able to go further, then maybe you should consider adding a second set of 2 12V batteries to make a second 24V battery source and a center-off toggle switch so you can switch between the two sets of batteries. The Currie Kit I installed this summer allows me to add a second 24V battery. The power toggle switch, which is a center-off toggle, can be switched to run off the appropriate battery pack. If you have a rear rack you might consider creating pannier bags to hold 2 sets of 12V batteries. Here's a You Tube video that shows such a mod on an ezip--this ezip owner has 2 sets of 24V 20AH SLAs. http://www.youtube.com/watch?v=qHYfWLOrUCc&feature=related That would give you a lower center of gravity and might make it easier to ride the bike. Good luck.

I got it I believe. The 3rd battery can't deliver 24v so it can't help.

I'm kinda thinking of electricity like I would water. As the original two batteries get drained the 3rd one would put some back. Like a spare gasoline tank.

Doesn't work that way. Thanks to all of you.