Batteries Question

[stele]

I have a 24 volt Vantage on the transom and I want to put a 36 volt Ulterra on the bow. Can I hook the vantage one battery short in series or does't it work that way? Haven't done anything yet just wondering. Thanks

[delcecchi]

I believe you could but I think it would be a bad idea since if the batteries get run down the third battery would  put a reverse voltage on the two that got discharged faster.   I believe that applying reverse voltage, effectively "charging" a battery backwards can damage the battery.

[leech~~]

You could do this if you put in an isolator to isolate the 2 battery when using the 24 V.  You would have to run wires for each motor separate and not have a loop system.

[delcecchi]

When you are using the 36 volt system are not all the batteries in series?

 

So, there is a danger of over discharging the two, as far as I can tell 

[papadarv]

10 hours ago, delcecchi said:

When you are using the 36 volt system are not all the batteries in series?

 

So, there is a danger of over discharging the two, as far as I can tell 

Del is correct 3ea 12v batteries in series are required to get 36v. 2 in series to get 24v and each battery 12v. You can connect a + and - wire to each individual battery, while wired in series, and run 3 separate 12v isolated devices. A + and - to either of 2 in series gives you 24v.

 

You NEED a "3 bank marine charger" which has 3+ and 3- charging wires which charges the 3 batteries independent of each battery. When one battery reaches full charge, that bank shuts off other 2 banks continue to charge until respective batteries are fully charged. Batteries will not overcharge. 

 

You can run both 36v and 24v motors on a 3 in series batteries but DON'T run both at the same time. Current draw on the 2 24v batteries will greatly reduce battery life and under serve current on the 36v motor.

 

Best solution is separate battery banks and chargers for each motor and a separate 12v for starting motor and running 12v electronics. 

 

Suggestion, carry a set of jumper cables long enough to reach from the battery bank to your primary motor battery. If your starter battery dies 5 miles off shore, just jumper to any one of the trolling motor batteries to start your engine.

[delcecchi]

All you guys still don't get it.   I didn't explain it well enough.    There are three batteries, each can hold 80 Amp hours.   

 

When the 24 volt motor is in use, two of the batteries use some of their capacity, equal for each battery.   So let's say you use 10 amps for two hours.   Now you have two batteries with 60 and one with 80.   Run all three (36 volt motor) for 6 hours at 10 and two batteries will be totally discharged and one will still have some charge.   Any further current draw will potentially damage the two batteries that are totally discharged.   

 

Of course the 36 volt motor will probably quit working as soon as two of the batteries are flat, but the concern is there.

[papadarv]

Lead acid battery discharge is voltage related not amp/current. Amp hours are time based on about a 15% drop in voltage which is the same voltage where a DC motor stops turning. 12v battery flat volts is about 10.5v & 36v battery at 30v & motors stop turning. If you don't turn the motor switch off, discharge will continue down to 0 volts but battery will recover when re-charged. Not good for the battery to drop volts to 0v as it reduces the life of the battery. Lead acid discharge rate chart showing volt loss.

[delcecchi]

It most certainly is amp-hours related, although the numbers vary somewhat by discharge rate.    The RC number on a battery is basically the amp hours at a specified discharge rate.   That curve above is for a particular battery.   

If you multiply the times by the discharge rate, looks like it is for 10 or 11 amp hour battery like the one in a Vexilar.   Multiply those currents by 8 or 10 for a trolling motor battery, so like 4 hours at 20 amps instead of 2.4 amps.   

 

Basically using one set of batteries for two different voltages strikes me as a bad idea.

[papadarv]

1 hour ago, delcecchi said:

 

Basically using one set of batteries for two different voltages strikes me as a bad idea.

I agree Dell, one set of batteries for 2 applications is a bad idea as I stated in my first post. Question was "will it work?" It will work, but its a bad idea.