Adding Batteries

[bob.fox]

I have a 144 volt system.  Comprising of 18 8v batteries.  My question is; can I add 2 or 4 batteries, of the same type, to this system without doing any damage to the controller or motor?  I have a curtis 8601 controller and the Advanced DC 120 volt motor.  My goal is to increase my range a little without carrying around a generator.  Is this possible?  Thanks.

Bob

[miodrag.zubic]

It's probably not a good idea. I am not positive about the 8601 but since it is rated for 144V it probably has 200 volt rated capacitors. Depending on the charger, your 144 volt system already gets charged to about 180 volts so adding even 2 8 volt batteries would be pushing it. Adding four is for sure not a good idea. When I say "pushing it" I mean that it would work, BUT you would be shortening life of capacitors and so the life of your controller. As far as motor is concerned, it is not as big a deal. Winding insulation is good for hundreds of volts anyway, and overspeeding the motor by a little (depending how you would drive it - gears vs. pedal) wouldn't hurt it much.

[terry.kane]

Just a thought, Bob:  If you have room to stow 22 batteries, you may want to consider 6V batteries.  22 x 6V = 132V versus your 18 x 8V.  You'll get a lot more range from this configuration.  Obviously, changing out 18 perfectly serviceable batteries makes no sense but perhaps you could find someone to buy your 8V pack and use that money to move to 6V.

[ted.karson]

So what if he added Capacitors with a higher voltage rating? Are ultra-capacitors a possibility? I do not recall any of our members exploring ultra-capacitors or AC induction motors or DC PM motors. Check out the AFS Trinity PHEV on youtube.

[bob.fox]

Just a thought, Bob:  If you have room to stow 22 batteries, you may want to consider 6V batteries.  22 x 6V = 132V versus your 18 x 8V.  You'll get a lot more range from this configuration.  Obviously, changing out 18 perfectly serviceable batteries makes no sense but perhaps you could find someone to buy your 8V pack and use that money to move to 6V.

I've thought about that Terry but this pack is less than a year old and I really don't want to do a whole re-config at the moment.  I thought when these were gone I may go to 24-6 volts. 

[bob.fox]

How about this?   What if I get 2 deep cycle 12v batteries put in a 12v inverter capable of running the charger?  How long do you think I could keep the charger running with these 2-12v batteries if wired in parallel?  Charger pulls about 17 amps.   How many AH's would I need to run the charger a couple of hours?   Am I out of the ballpark here?

[terry.kane]

That idea's just crazy enough to work!  Do you know your present Wh per mile?  You can probably predict the "range benefit" of implementing your idea by taking the Wh in the auxilary batteries, assuming a loss rate (like 50%?) due to inverter/conversion/charging losses.  EV's range from 200 Wh/mile and up.  Your Mustang is probably in the 350 Wh/mile range. 

If your twin 12V batteries can produce 100 Ah each with a short discharge duty cycle, then you've got 200Ah at 12V to work with .  200Ah x 12V = 2400Wh.  If the losses are 50%, then you can theoretically deliver 1200Wh to your batteries, assuming the inverter and charger can deliver the same in the given time.  So 1200Wh/350WH/mile = <4 miles.  Is it worth it?

Another way of looking at it Ted's rough rule of thumb that every Flooded 6V PbA (or equivalent) battery gives you 2 miles.  e.g. his 20 batteries = 40 miles.  Your 18 batteries should give 36 miles or so (more cells but fewer plates in 8V batteries).  Your 2 large 12V batteries might be the equivalent of 4 6V batteries so, again 4 miles, at most (factoring losses)?

This is not definitive - I've included many assumptions and I'm still not sure my calculations are correct.

[bob.fox]

No one has accused me yet of being sane.   

350 w/h's is probably real close.   Batts are 178 AH's.  I can get 40 miles on warm days and nights.  I don't have them insulated nor heated yet. 

I have a 32 mile round-trip commute.  My employer is being stubborn ( I would use other adjectives but we have to keep the forum clean) on letting me plug in.  On these cold mornings and 50* days I'm barely making it home.  The extra 4 to 8 miles would be wonderful. 

[miodrag.zubic]

Two things to keep in mind if you go ahead with this:

1. Most inverters generate square-wave ac voltage. Depending on what charger you have, it may or may not be a problem. Newer ones are probably fine, but some older ones (or home-made) may run hot.
2. It is probably a good idea to use your aux batteries to charge your main pack while not driving (while at work). If you charge while driving, again depending on what charger you have, it might not like it when your main pack voltage dips down during acceleration.