# reducing 14v dc to constant 12vdc

Discussion in 'The Projects Forum' started by Pistolpete, Oct 14, 2012.

1. ### Pistolpete Thread Starter New Member

Oct 14, 2012
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I put a new kawasaki engine on a piece of equipment that has many electrical relays to run electric hydraulic controllers. engine voltage regulator is putting out 14 v dc. Kawasaki doesn't have a differant regulator for this engine. I am told the relays will fail if i don't get them steady 12v current.
The inline fuse is 15amp to the control panel. Is there a inline current regulator that can reduce the voltage from 14vdc to 12vdc with 15 amp draw. As you can probably tell by my lingo i am not very knowledgeable about electronics.

Any suggestions would be very helpful in correcting this problem.

Thanks
Pete

2. ### takao21203 AAC Fanatic!

Apr 28, 2012
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As for relays, and 2V reduction, 3x power silicon diodes in series can be used.

3. ### wayneh Expert

Sep 9, 2010
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I'd look into that, since frankly I don't believe it. But if you want to proceed, the diode trick as mentioned will work. You need to be sure the diodes are rated for at least the current passing through them, and a bit more for safety factor. This might mean putting only, say, 5A through any one string of diodes. You could have a string of 3 for each relay, or a one single, high current string for all of them, or any arrangement in between.

If you are only protecting relays, you could also consider a current limiting resistor for each. The current passing through each is predictable, so it wouldn't be hard to calculate the right value to drop 2V.

4. ### panic mode Senior Member

Oct 10, 2011
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i agree, lookup relay datasheet and you will see why...

i don't know what relay you have but here is an example of miniature automotive high current relays from Duracool.

12V version obviously works at 12V but minimum voltage is 6.9V. This is nearly half of rated 12V. check the maximum allowable voltage and it is 27.2V. this is more than double of rated 12V. oh and if temperature is over 85degC, this is reduced to 72% or 0.72*27.2=19.6V which is still good deal higher than rated 12V. you probably don't want to operate them at or near limit values but change of 2V in this case is nothing.

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5. ### takao21203 AAC Fanatic!

Apr 28, 2012
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Depends if the relays are enclosed or if there is airflow. If relays are powered for long time, or if there is even overvoltage, they will get hot.

You should run a long-time test. Eventually the relays can tolerate 14V.

Relays also can latch after some time, depending on the load current, especially so if they are used to start motors. Overvoltage could accelerate this further. Latching means, the magnetic anchor will remain stuck even after coil current is switched off. In some cases it is sufficient just to tap the relay with a screwdriver etc., nonetheless it is undesireable.

From my experience 12V or 14V should not result in a large difference, but I don't know the type or size of these relays. And power diodes aren't expensive. They may require cooling as well. If you need to work many smaller relays, it might be cheaper and easier to purchase a small reel/piece of tape for regular diodes. Many TO220 diodes are actually schottky-type, their drop voltage depends on the load current. If the current is low, it might be only .4 to .5 volts.

Aug 12, 2012
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7. ### bountyhunter Well-Known Member

Sep 7, 2009
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Most relays or electronic devices built for "12V use" are actually designed to handle 14V since, as you found out, all "12V" auto/MC systems actually regulate to 14V since that is what the basic 12.6V lead-acid battery is charged to in a car or motorcycle. I doubt very much the relays would die if hit with 14V. Relays die from the contacts burning out, not the coils.

8. ### takao21203 AAC Fanatic!

Apr 28, 2012
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It's unlikely. However if there is a battery connected in parallel to the electric system, voltage won't go much higher than 12V at all.

Sometimes I saw information about 13.6V or 13.8V, not 14V; not that it would make a large difference.

9. ### bountyhunter Well-Known Member

Sep 7, 2009
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??????????????

Take a voltmeter out and put it on the battery in your car. Start the engine and hold the engine at about 2000 RPM for a couple of minutes. The battery voltage will come up to about 14V in a very short time, assuming you have a working battery. Measure it and see. The electrical regulator on cars and motorcycles holds the battery at about 14V when operating. The regulator spec is typically about 14V with a 3% tolerance.

10. ### takao21203 AAC Fanatic!

Apr 28, 2012
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Well the meaning was more of a kind that usually people consider this voltage to be 12V (even if it is actually not correct). And the little difference in reality is neglible. And I mentioned the 13.6V/13.8V specification, which actually exist for some power supplies. Most if not all 12V circuits are also suitable for 13.6V or 13.8V, but somewhere a line is drawn. This would be let say 18V (a too high voltage).

http://landiss.com/battery.htm

I don't really suggest automotive illustrations, even if the original topic isn't automotive.

I am told the relays will fail if i don't get them steady 12v current

I have some ?????? about that

It really depends on the specification of the relay board. Which should exist somehow.

I would have to see the relays, maybe remove the covering from one of them. Then I can decide if it is appreciate to connect them to 14V. And then observe for some hours to some days. If the coils get hot quickly, then 14V aren't appreciate.

On the other hand, halogen bulbs specified for 12V are often worked at slightly lower voltage, for instance 11.5V

So this hydraulic control panel might be a special case- designed for "automotive" voltages, but not being automotive as such.

Last edited: Oct 14, 2012
11. ### Ron H AAC Fanatic!

Apr 14, 2005
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7812 needs at least 2.5V across it to work properly.

12. ### takao21203 AAC Fanatic!

Apr 28, 2012
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And they can't be used for 15 Amps. The OP either could ignore the warning and use the board with 14V regulator, or install some diodes. It is not complicated to do it, nor are they expensive. Actually small relays are unlikely to draw large currents. I suggest to check the current with an Amp meter.

Because the diodes aren't expensive, maybe install a few just to be safe. Even if myself I would eventually use it with 14V.

13. ### vk6zgo Active Member

Jul 21, 2012
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I would suggest that "12V" relays would be quite happy at 14V.

24V relays were commonly used on the "24V rail" used in most of the TV & Radio sites I worked on back in the day.

The "24V" was supplied by a mains operated supply while the mains were available,& by batteries when the mains were lost.

This voltage went as high as 28V at times,with no problems caused to the relays.

These were ordinary,everyday relays, not Automotive relays,which are designed to tolerate such voltage excursions.

14. ### Ron H AAC Fanatic!

Apr 14, 2005
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I agree. Automotive relays are called "12 volt" relays, but they routinely are subjected to voltages as high as ≈14.5V when the engine is running and the battery is being charged. I suspect that the OP's relays are "12 volt" relays in the same sense.

15. ### takao21203 AAC Fanatic!

Apr 28, 2012
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Maybe the technician was refering to a stabilized 12V supply, not some chopped DC from a generator. Not very likely to damage the relays directly, but it can cause malfunction.

These 12V generators are normally 3-phase so there is just some ripple.