Well, here I go again messing around. I have a mobility scooter I was planning to add a 6V battery in series with the two 12V existing batteries for a "Turbo"
scooter....not really, was really goibg to have it switchable in case the batteries get low for a near normal speed, a temporary fix to a temporary problem.

My initial test, however reviled that there must be some sort of voltage limiting circuitry in on the main controller board.

I do know that it does run on voltages between 23 - 27V based on whether the batteries are fully charged or needing to be charged.

My thoughts are to add the 6V battery, make it switchable, and regulate the output to 27V. I am thinking along the lines of a LM350 IC but think that this may fry up in no time. Should I measure the current draw first?

 

Of course you need to measure the current and how much current does the motor draw if it gets stalled. Then you have to choose the appropriate power MOS which will drive the motor. Have a look here:

http://www.nxp.com/acrobat_download/applicationnotes/APPCHP3.pdf

 

As the pair of 12v batteries become exhausted, their internal resistance will increase considerably.

The addition of a 6v battery in the string won't help very much, I'm afraid.

Better to keep track of your power utilization, and be in a place to either charge or exhange the batteries for a fresh set before they're exhausted.

I don't know what kind of batteries that wheelchairs use, but if they're some kind of lead-acid batteries, they will last considerably longer if they are never discharged more than 30%.

If you routinely run them down past 50% charge, they will have a greatly shortened service life. Getting them too hot or trying to charge or discharge them too fast (which also results in internal heating) will also shorten their service life.

 

As the pair of 12v batteries become exhausted, their internal resistance will increase considerably.

The addition of a 6v battery in the string won't help very much, I'm afraid.

I am never disappointed by your feedback Sgt. You always exert patience when passing judgment and seem to always have pertinent questions.

Better to keep track of your power utilization, and be in a place to either charge or exhange the batteries for a fresh set before they're exhausted.

In my scenario I was considering switching the 6V battery on when the scooter was noticeably slower. What if I keep the 6V battery in the loop and use the voltage regulator the maintain the normal two-battery max of 27V. Would this be some improvement, increasing the Ah rating overall? Maybe my main issue are the steep hills I have to go up from my home regardless of the direction I go. They can't be avoided. The degree of incline, I believe, is greater than the max stated in the manual, thus resulting the decreased lifespan of the batteries.

I don't know what kind of batteries that wheelchairs use, but if they're some kind of lead-acid batteries, they will last considerably longer if they are never discharged more than 30%.

This is a concept I am unsure of... 30 of what? In other words the battery voltage should not go below X volts, and in the case of the 12V AGM battery this would be _____V_?

If you routinely run them down past 50% charge, they will have a greatly shortened service life. Getting them too hot or trying to charge or discharge them too fast (which also results in internal heating) will also shorten their service life.

This is the same concept as the %30 deal... Are the %30 and %50 related to the fully charged voltage and the minimum charged battery, say 13.5V and 11.5V?? The difference her is 2V and %50 would be 12.5V, %30 would be 12.8V. If this is the case It would not take much on these hills to knock them down below 30, let alone %50. I don't know the exact voltage but I know that under heavy load(the uphill clime) the voltage does drop considerably. Would batteries with a higher Ah rating improved things any?

I do charge them after each use, approximately 2 miles, bye the scooter manual states they can power the scooter up to 25 miles...flat surface.

 

In my scenario I was considering switching the 6V battery on when the scooter was noticeably slower. What if I keep the 6V battery in the loop and use the voltage regulator the maintain the normal two-battery max of 27V. Would this be some improvement, increasing the Ah rating overall? Maybe my main issue are the steep hills I have to go up from my home regardless of the direction I go. They can't be avoided. The degree of incline, I believe, is greater than the max stated in the manual, thus resulting the decreased lifespan of the batteries.

Your best bet would be to get two 12v batteries with a higher AH rating.

As I've already mentioned, by the time your 12v batteries are becoming discharged, their internal resistance increases, so adding a 6v battery in series won't give you the desired boost.

This is a concept I am unsure of... 30 of what? In other words the battery voltage should not go below X volts, and in the case of the 12V AGM battery this would be _____V_?

Your battery manufacturer should be able to supply you with that information.

The actual voltage will vary due to battery chemistry, core temperature, and charge.

This is the same concept as the %30 deal... Are the %30 and %50 related to the fully charged voltage and the minimum charged battery, say 13.5V and 11.5V?? The difference her is 2V and %50 would be 12.5V, %30 would be 12.8V. If this is the case It would not take much on these hills to knock them down below 30, let alone %50. I don't know the exact voltage but I know that under heavy load(the uphill clime) the voltage does drop considerably. Would batteries with a higher Ah rating improved things any?

Yes, higher AH rated batteries would definitely help. You should use the highest AH rated batteries that you can get, that are rated for deep cycling. They'll be heavier, but since they are located low in the scooter, it will help the scooter's stability.

But really, you should look for a scooter that is rated to handle the inclines in your area. You might have to use something that's gasoline, propane or hydrogen powered.

I do charge them after each use, approximately 2 miles, bye the scooter manual states they can power the scooter up to 25 miles...flat surface.

25 miles on a flat surface is VERY different from 2 miles on a steep incline.

 

This evening I did a test. I connected my Digital Meter to one of the batteries of my scooter and monitored the voltages at varying demand.

Still - 13.50V
Full on Level ground - 12.90V
Full up steep incline - 12.50V

after about 1.2 miles/up steep incline - 12.20V

Final resting voltage - 12.9V

It appears that the inclined are indeed stressing the batteries quite a bit.

The original batteries were rated at 32Ah but I have found suitable replacements that fit in the scooter with 35Ah ratings. I often run the scooter without the cover, thus allowing me to use larger batteries if I really wanted to, but it's not likely I could get anything much larger than about 40Ah.

I may have to press the doctor for a scooter with greater capacity. This one would work in the house.

Thanks for the insight.

 

That 13.5v reading you were getting is a "surface charge" left after "float" charging. It's not a real reading. If you removed the "float" charger and let the battery sit for 4 to 6 hours, it would likely settle to somewhere between 12.6v-12.9v.
35AH batteries would only be around a 9% improvement over your 32AH batteries - but any improvement is something.

I believe your best arguement will be to show the doctor the maximum incline rating of the scooter, along with an elevation survey of the area surrounding your home; your county office should have that kind of information. If the terrain's inclines exceed the rating of the scooter, then it is not safe.