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Old 10-08-2011, 02:03 PM   #1
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Voltage reducer 13 to 12 VDC


Hello,

I have a golf cart that has a +12VDC accessory light bar. The cart has (8) 6.5V batteries installed. We have two batteries in series providing +13VDC to the light bar. The light bar runs fine, it just runs a little bright and a couple of the strobes have died prematurely. I came across a 16/18V -> 12V voltage reducer but it provides too much of a reduction from a measly 13V, dropping it down to about 10.75V.

Does anyone know of a way to provide a simple +13VDC to +12VDC voltage reduction?

Thanks for your help.

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Old 10-08-2011, 02:57 PM   #2
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Voltage reducer 13 to 12 VDC


You would have to use a resistor to drop the voltage. You will need to find out how many ohms the load is, you can try a varistor, vs. hard wiring in a resistor.

http://www.ehow.com/how_4900110_redu...resistors.html
http://www.ehow.com/how_7618478_calc...resistors.html
http://www.eham.net/ehamforum/smf/in...;topic=23221.0
http://search.yahoo.com/search;_ylt=...&fr=att-portal

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Old 10-08-2011, 03:17 PM   #3
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Voltage reducer 13 to 12 VDC


Is this light bar from an automotive application?

If so, then 13Vdc should not have hurt it. The typical automotive electrical system will go up to about 14.5 Vdc when the engine is running. If the lights are too bright, then change the bulb to a lower wattage.

Have you actually measured the voltage going to the light bar or are you just assuming that it's 13 Vdc?

One other thing....I would not operate the light bar while the cart is being charged...the actual voltage across those batteries will be more than 6.5/bat.
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Old 10-08-2011, 04:41 PM   #4
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Voltage reducer 13 to 12 VDC


Quote:
Originally Posted by alkiser View Post
Hello,

I have a golf cart that has a +12VDC accessory light bar. The cart has (8) 6.5V batteries installed. We have two batteries in series providing +13VDC to the light bar. The light bar runs fine, it just runs a little bright and a couple of the strobes have died prematurely. I came across a 16/18V -> 12V voltage reducer but it provides too much of a reduction from a measly 13V, dropping it down to about 10.75V.

Does anyone know of a way to provide a simple +13VDC to +12VDC voltage reduction?

Thanks for your help.
Did you measure the voltage? What kind of batteries are these? 6.5V doesn't correspond well to any combination of lead acid cells (2V each nominally), unless it's a 3-cell battery and mostly charged perhaps? Regardless, a normal car battery is not 12V unless it's almost dead. Normal fully-charged voltage is 14.7 or so, and automotive equipment needs to handle up to 24V or so for brief periods. A 13V nominal system should work fine with any automotive equipment. What is the actual voltage during operation?
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Old 10-08-2011, 04:46 PM   #5
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Voltage reducer 13 to 12 VDC


Quote:
Originally Posted by gregzoll View Post
You would have to use a resistor to drop the voltage. You will need to find out how many ohms the load is, you can try a varistor, vs. hard wiring in a resistor.

http://www.ehow.com/how_4900110_redu...resistors.html
http://www.ehow.com/how_7618478_calc...resistors.html
http://www.eham.net/ehamforum/smf/in...;topic=23221.0
http://search.yahoo.com/search;_ylt=...&fr=att-portal
A resistor is only usable for this if the load is very consistent, which this probably wouldn't be. The better solution is to use diodes. Their voltage drop is constant regardless of current (mostly). Each regular silicon diode will drop 0.4-0.6V, so a stack of 2-3 in series should drop about a volt. For larger voltage reductions, zener diodes provide controlled voltage drops ranging from a couple volts up to hundreds.
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Old 10-08-2011, 08:16 PM   #6
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Voltage reducer 13 to 12 VDC


The trouble with using a resistor is that unless the load is always
constant the voltage drop will vary accordingly.
What you want is some thing that has a constant voltage
drop reguardless of load.
And there is,
Use two large power diodes.
The voltage drop across each diode is around .4v to .6v.
So two in series would work real well.
Al you have to do is figure out what the maximum load is,
Then select the appriopriate rated diode.
I would go for 5a or 7a diodes.
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Old 10-08-2011, 09:09 PM   #7
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Voltage reducer 13 to 12 VDC


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Originally Posted by alkiser View Post
The light bar runs fine, it just runs a little bright and a couple of the strobes have died prematurely
The strobes don't run off of 12v or 13v. The power pack handles the voltage, and it's much higher than 12v, often 300v or more.

As DDawg said, if these are automotive strobes then there is no problem with them running on 13v.
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Old 10-08-2011, 09:33 PM   #8
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Voltage reducer 13 to 12 VDC


[quote=AandPDan;744818]The strobes don't run off of 12v or 13v. The power pack handles the voltage, and it's much higher than 12v, often 300v or more.

Whilst the zenon tubes do indeed require 300v or more to work,
There is usually an inbuilt step up circuit to supply this from the 12v.
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Old 10-09-2011, 01:18 AM   #9
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Voltage reducer 13 to 12 VDC


Hey everyone thanks for your replies.

Here is the lightbar I have installed:

http://www.whelen.com/install/136/13657.pdf

I have the version without the traffic advisory signal.

Yes I did rate the voltage with a meter and it comes to 13v, although I now realize that the cart was freshly charged so the batteries may actually be 6v. I also then realized that the golf cart (per the manual) is a 48v so that divided by 8 batteries gives me my 6v per battery.

Thanks for the tip about running the lightbar while it's charging. These carts are used by people everyday, so I'll make up a note to tell people to unplug the cart before testing the lightbar.

I suppose it's probably true that the lightbar should be able to handle variations in voltage, it would just be nice to be able to regulate or normalize it somehow to keep it as close to spec as possible.
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Old 10-09-2011, 04:18 AM   #10
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Voltage reducer 13 to 12 VDC


Quote:
Originally Posted by alkiser View Post
I suppose it's probably true that the lightbar should be able to handle variations in voltage, it would just be nice to be able to regulate or normalize it somehow to keep it as close to spec as possible.
There is absolutely no need or reason to provide regulated voltage to the light bar. There's also no need or reason not to use it while charging. Vehicle electrical systems are charging only while the engine is running, so the light bar is designed to operate at a normal charging voltage of 14.2-14.7V. 12V is not the spec voltage for a vehicle electrical system, it's the nominal voltage. The actual operating voltage is 14.2-14.7V, and the Whelen light bar is designed for that. Operating at a lower voltage may actually be worse for it if the strobe inverter operates in a constant-power mode, because lower battery voltage would result in increased current draw.
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Old 10-09-2011, 10:11 AM   #11
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Voltage reducer 13 to 12 VDC


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Originally Posted by mpoulton View Post
There is absolutely no need or reason to provide regulated voltage to the light bar. There's also no need or reason not to use it while charging. Vehicle electrical systems are charging only while the engine is running, so the light bar is designed to operate at a normal charging voltage of 14.2-14.7V. 12V is not the spec voltage for a vehicle electrical system, it's the nominal voltage. The actual operating voltage is 14.2-14.7V, and the Whelen light bar is designed for that. Operating at a lower voltage may actually be worse for it if the strobe inverter operates in a constant-power mode, because lower battery voltage would result in increased current draw.
Ok thanks. Looks like everything is just fine then.
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Old 10-09-2011, 06:05 PM   #12
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Voltage reducer 13 to 12 VDC


If the strobes are failing early, there may be other problems at play. The supply voltage probably isn't it, though. Are the strobe power supplies mounted somewhere exceptionally hot?

Last edited by mpoulton; 10-10-2011 at 12:34 AM.
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Old 10-09-2011, 10:59 PM   #13
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Voltage reducer 13 to 12 VDC


It's really hot during spring and summer out here. I've asked to get at least some kind of awning or covering for our "cart barn" but haven't had much luck.

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