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Old 06-26-2011, 02:46 AM   #1
JohnnieB
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Default Potential solution to Aux Power issues.

My recently acquired 2008 TXT PDS is plain vanilla, but MP3 Player, GPS and lighting are on the to-do list, so I’ve been reading posts about Aux Power issues.
Some people tap the battery Pack, others have installed a separate 12v battery and still others use a DC to DC converter, but all have issues. (Imbalanced batteries in pack, the need for separate chargers and expense, etc.)

I haven’t tried this yet, but here's some food for thought and discussion.

One possible solution is wiring two 12v light bulbs in series with a 12v auxiliary battery that is connected across the 36v battery pack. (Three 12v bulbs for a 48v battery pack)
That way the individual batteries in the battery pack stay balanced, only one charger is needed and expense is minimal.

For those that aren’t familiar with how a light bulb works, it’s a poor man’s voltage regulator, current limiter and fuse.
Electrically, the filament is a resistor with a positive temperature coefficient, which means the resistance increases as the temperature increases.
(The fact that the filament gets hot enough to give off light is incidental in this application)
Basically, the resistance will increase as the filament gets hotter until the voltage drop across the resistance equals the applied voltage. (In this case, sum of voltage drops equal applied voltage)

If the 12v battery was connected directly to a 36v battery pack, the current flow would be hundreds of amps and bad things would happen, but with two #1056 single contact bayonet auto bulbs in series, the max current would be limited to about 2.1 amps and would taper off due to the Aux battery’s terminal voltage increasing as it took a charge. (I used a #1056 for an example, but auto light bulbs come in a wide variety, so pick one whose specs match the maximum current flow you want.)

Also, add a diode in series to prevent current flow from the Aux Battery back to the battery pack. Probably wouldn’t be much, but it would be zero with a diode in place. A fuse might be a good idea too. It will discharge the main battery pack, so a switch of some kind might be a good idea also.

Net result, Aux Battery would receive a charge at same time as main battery pack and be trickle charged from battery pack full time.

FWIW: I’ve seen bulbs used in this manner in the charging circuits for gel-cells in some very critical medical devices, that’s where my idea came from.

BTW: An 8v battery can be charged with a 12v battery charger if you put a 12v bulb in series with it.
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Old 06-27-2011, 07:25 PM   #2
1toolman2
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Default Re: Potential solution to Aux Power issues.

can you kind of draw this out and post it?
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Old 06-27-2011, 08:14 PM   #3
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Default Re: Potential solution to Aux Power issues.

Quote:
Originally Posted by JohnnieB View Post

It will discharge the main battery pack, so a switch of some kind might be a good idea also.
That would happen with or without the bulb. I would like to be there with a camera when you try to hook up a 12v battery to a 36V string. If you try to hook it up to 2 of the 6v batteries, bulb or no bulb, you're gonna have an unbalance in the string.

The bulb just acts as a current limiter. I use to use this trick when locating a fuse that blows intermittently in 48v Telco equipment.
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Old 06-28-2011, 02:23 AM   #4
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Default Re: Potential solution to Aux Power issues.

Quote:
Originally Posted by OlManRivah View Post
.........I would like to be there with a camera when you try to hook up a 12v battery to a 36V string.
I am Not, repeat NOT, suggesting anyone connects a 12v battery directly to a 36v string. Doing so would very like cause acid and flash burns.
What I am suggesting is connecting two 12v light bulbs and a 12v battery wired in series to a 36v string.

Basically, it is a voltage divider. The first bulb drops 12v and the second bulb drops 12v, leaving the remaining 12v to be dropped across the 12v battery.
(These are approximate voltages due to the fact neither light bulbs nor batteries operate at the identifying voltage assigned to them.)

Since the terminal voltage of a battery increases as it charges, the current through it decreases if the charging voltage remains constant, but the resistance of the light bulb decreases when current flow decreases, so less voltage is dropped across the bulb and the charging voltage to the battery increases, causing the current flow in the series circuit to increase.
After some pushing and shoving, quiescence is reached.

Max current with a discharged battery is whatever the bulbs are rated at and IIRC, the trickle current after battery reaches full charge is about half of bulbs rating

Quote:
Originally Posted by OlManRivah View Post
.........If you try to hook it up to 2 of the 6v batteries, bulb or no bulb, you're gonna have an unbalance in the string.
True. However the two bulb and battery in series goes across the entire 36v string, so there is no imbalance, which is the purpose of this Rube Goldberg contraption.

Quote:
Originally Posted by OlManRivah View Post
........The bulb just acts as a current limiter.
The voltage regulation aspect of a light bulb may be debatable, but it also acts as a fuse, should the 12v battery get a bad case of shorted cells.


Quote:
Originally Posted by OlManRivah View Post
......I use to use this trick when locating a fuse that blows intermittently in 48v Telco equipment.
I've used light bulbs for a lot of things Edison never imagined also.
The first time I saw a light bulb used in a battery charging circuit was in a MRL Defibrillator back in the early eighties.
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Old 06-30-2011, 08:04 PM   #5
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Default Re: Potential solution to Aux Power issues.

Would 3 12volt lights in series run on 36 volts?

From Wikipedia "Series circuits were formerly used for lighting in electric multiple unit trains. For example, if the supply voltage was 600 volts there might be eight 70-volt bulbs in series (total 560 volts) plus a resistor to drop the remaining 40 volts"

would something like this work for 36 volt with 3 12 v lights
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Old 07-01-2011, 12:32 AM   #6
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Default Re: Potential solution to Aux Power issues.

Full disclosure: I'm new to golf carts, but I'd been working with electricity and electronics for over 50 years when I retired a couple years ago, plus a few other disciplines for the last 40 years.

Yes, three 12v light bulbs wired in series will work on a 36v supply. (or 12v bulb x 4 for 48v, or 12v bulb x 6 for 72v)
Use bulbs with identical ratings in series strings if you want equal brightness.
Otherwise the lowest wattage bulb will glow about normal and the higher wattage bulbs will be dimmer than normal.
(The same current flows through all elements in a series circuit, so the current flow will be restricted to what the lowest wattage bulb will pass.)

One of the more common applications of low voltage bulbs wired in series and connected to a higher voltage source are the strings of Christmas Tree lights were the whole string goes out when one bulb burns out.
FWIW, Non-contact voltage testers are great for finding the bad bulb in string of Xmas Lights.
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Old 07-01-2011, 05:26 AM   #7
bacord
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Default Re: Potential solution to Aux Power issues.

If all wattage is the same on the lamps, would the life span of the lamps be decreased? Also is there a way to add a 12 volt battery in parallel at the end of the 36 v to use as a aux battery and still have 36 volts at the end of the string of batterys and still use 36v charger?
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Old 07-01-2011, 08:01 AM   #8
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Default Re: Potential solution to Aux Power issues.

This is a very interesting discussion, any kind of drawing would greatly help everyone follow along ....

Download Google sketchup7 or any simple free drawing program if you have none.
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Old 07-01-2011, 10:02 AM   #9
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Default Re: Potential solution to Aux Power issues.

Quote:
Originally Posted by bacord View Post
Also is there a way to add a 12 volt battery in parallel at the end of the 36 v to use as a aux battery and still have 36 volts at the end of the string of batterys and still use 36v charger?
Oops.....there's that unbalance again. It'll work....but......
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Old 07-01-2011, 10:57 AM   #10
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Default Re: Potential solution to Aux Power issues.

Quote:
Originally Posted by bacord View Post
1-If all wattage is the same on the lamps, would the life span of the lamps be decreased?
2A-Also is there a way to add a 12 volt battery in parallel at the end of the 36 v to use as a aux battery
2B-and still have 36 volts at the end of the string of batterys and still use 36v charger?
1. Same wattage bulbs in series - Life span will be normal.
Different wattage bulbs in series - Life span of lowest wattage bulb(s) will be normal and life span of higher wattage bulbs will be extended.

2A. Not sure exactly what you mean. If you put a 12v battery in parallel with of one of the bulbs, the current flow through the bulbs in series would be split between the bulb paralleled by the battery and the battery. Why not replace one of the 3 bulbs in series with a 12v battery as originally suggested?

2B. Not sure exactly what you mean. If the 3 12v elements in series (bulbs or batteries or mixtures thereof) are paralleled across the main 36v battery pack, the standard charger will work.


Sidebar: Since you questioned the life span of light bulbs, I'll toss in a bit of info on it.
A small reduction in operating voltage will greatly increase life span while slightly lowering light output.

For example, I had a remote alarm panel with dozens of lights that burnt out quite often and were a royal pain to change. I replaced the 24v bulbs with 30v bulbs and never had to replace another burnt out bulb. The 30v bulbs were noticeably dimmer, but they were indicators rather than used for illumination, and the people that watched the remote alarm panel were happy they didn't have to keep remembering which bulb was out until it was replaced.
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