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Old 19-01-2010, 20:41   #1
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Stabilizing Onboard 12vdc

Now that we have a wind generator, our on board voltage varies from 12.6v to 14.4v depending on the breeze and the Lighting LED's don't like that variation very much. I am thinking to put a low voltage drop voltage regulator in each lighting circuit to give me a stable output but I don't know how to read the specification sheet. For example, it states that voltage regulator LM 1085-IT-12 will take an imput voltage of 5-18v, and give an output voltage of 12v @ 3 amps with a voltage drop of 1.5volts. So what does that mean?? Do I get 12v, or do I get 12v minus 1.5v? I will be happy to get a voltage of 11 - 12v, so long as it is steady and doesn't drift all over the place depending on the imput voltage. Is that possible?
As always, all assistance gratefully received.
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Old 19-01-2010, 23:33   #2
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"dropout" refers to the voltage differential between the regulator's input and output. Typically this means you need at least the dropout voltage differential.

So in this case (from the spec sheet "The LM1085 is a series of low dropout positive voltage regulators with a maximum dropout of 1.5V at 3A of load current."), for an output of 12VDC, you need an input voltage of at least 13.5VDC. The dropout probably is less at lower load, but would have to read the datasheet to know more.

[EDIT: Here's the complete datasheet http://pdf1.alldatasheet.com/datashe...1085IT-12.html - and from that you can see the dropout at different loads, for example at .5A it's around 1V, depending on temperature]

NOTE: I'm an amateur at electronics at best, so assume everything I say is wrong :-)
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Old 20-01-2010, 00:35   #3
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Thank you Scottie.
So, since I'm only wanting to feed a few LED's, my current draw will be well short of the 3 amps that the regulator supplies, so the voltage drop will be correspondingly reduced as well - perhaps only 1v or even less?
Since we never run our system below 12.4v, this would give a more or less stable voltage of say 11.4v minimum which would suit me just fine. But do I understand it correctly that if its a 12v output regulator with a 1.5v dropout, then once the imput voltage is 13.5v or higher, then the output voltage will not exceed 12v? In other words, the dropout V only affects the output if the imput is below 13.5v? Sorry if this all sounds a bit dumb, but I'm not experienced in these 'black'arts...
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Old 20-01-2010, 06:23   #4
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Good LED light fittings should come with voltage regulator. Discover how a voltage regulator behave by experimenting, they do not cost much money.
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Old 20-01-2010, 08:26   #5
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I'm honestly not sure what happens to the output if the input differential drops below the dropout range. I agree, if the output is just reduced, then it's probably just fine for this instance...
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Old 20-01-2010, 12:20   #6
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Chris
There are marinised 12v regulator units available quite cheaply which will do what you want and more. I have one stabilising my whole 12v system, lights, instruments, the lot. I just couldn't see the point of stabilising one electrical circuit and not doing it all, sure, most instruments are rated for an input range somewhere between 12 - 14.5 volts, but to me it makes more sense to know they're on a constant voltage.
I'll confess to being biased here, when I was a seagoing Electronics Officer, problems caused by variations in supply - even relatively small variations in supply - were a pain in the butt.
I put a regulator into my boat for around NZ$100
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Old 20-01-2010, 16:30   #7
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The behaviour of the regulator when the input drops should be mentioned in regulators papers. Some cut off. Some lower the output voltage, etc.. Ours beeps and cuts off (waeco).

b.
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Old 20-01-2010, 17:20   #8
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I would like to put a 12 volt regulator/spike arrestor on my 12 volt buss. My concern is more one of spikes rather than variability in the 12-14 volt range. I plan to replace my halogen lamps and running lights with LEDs and semiconductors are much more sensative to voltage spikes than the conventional bulbs. Al, do you have a brand name? The only one I could find in the States does not seem to have survived the recession.
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Old 20-01-2010, 23:38   #9
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Al, Ditto Captain Bill's question.
I did find a locally produced little box of tricks that accepted 10 - 16vdc and gave out a steady 12vdc/8amps - more than sufficient to put all my electrical need through. The only trouble is it costs NZ$350 whereas a voltage regulator costs $1.35. I would dearly love to have that little whizz-bang box but, usual story, retired - full time cruising - limited money coming in.....
Are you able to recall from where you sourced your 12v regulator unit?
Chris
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Old 21-01-2010, 00:17   #10
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Cap"n Bill
I'll have to check on the brand - it's an obscure import, but has been working admirably. I'll be up on Silhouette at the weekend and get back to you. There MUST be others around who make them in your neck of the woods, I'll have a poke around and see if I can come up with anything. How about Waeco - that was what Barnakiel has, I think its a similar thing.
Chris
Trademe is a wonderful place. Mine handles between an 8 - 15V input, and gives a steady 12V output. The model I have cost $99, and gives me a 10 amp capability, more than enough for my lights, VHF, and Depth thingie all to be running at the same time. There's also a lower rated model (5amp) for about $75. The only thing I have to watch is that I don't over-discharge the house battery, going down to 8volts isn't a great idea! Look in trademe boats / radio&electronics, search for regulator
Hope this helps
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Old 21-01-2010, 10:20   #11
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The voltage regulators are indeed only $1.35. The issue is they don't solve the problem of spikes. The cheapest regulators, like an LM317 also require the input voltage be some specified amount over the output voltage. If the input voltage drops below the output voltage they can't help. Buck/boost regulators are not much more expensive but can handle the lower voltage. One issue with these is that they "chop" the DC at radio frequencies and if the circuit is not properly designed can cause radio interference. Most "marinized" devices are designed not to interfere with your radios as well as being able to operate in humidities over 95%.

The voltage regulators themselves are suseptable to voltage spikes. As analog devices they tend to handle it a bit better than digital, but voltage spikes cause them to deteriorate over time. I have been able to find marinized 12V and 24V surge/spike protectors, but not in combination with a voltage regulator and at a cost of nearly $400US. There are automotive/marine regulators available at a reasonable price, but they are really aimed at the automotive market with a minimum input voltage of about 13.4. The manufacturer seems to assume that if your using the device you'll have your engine running. That may be true most of the time in a car, but not on a sailboat. Most of the regulators and protectors for the computer market have a maximum input voltage of 13.5-14, which is too low for use on a boat.

There are really cheap 12 volt spike protectors, but they are built using diodes and fuses. While a bit better than nothing, they don't offer the protection of an MOV based device. Diodes can easily be destroyed by voltages above their rating which is usually in the hundreds of volts. MOVs however can handle 10000 volts. MOVs however have to be considered sacrificial since their capacity to absorb spikes has a lifetime limit dependent on the voltage and amperage of the surge absorbed. I would guess one would not want to combine the two functions in single circuit package since you would have to throw out the regulator every time the MOV reached it's capacity. $400 seems a bit steep for a surge protector, even an MOV based one.
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Old 21-01-2010, 10:49   #12
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Quote:
Originally Posted by Captain Bill View Post
... There are really cheap 12 volt spike protectors, but they are built using diodes and fuses. While a bit better than nothing, they don't offer the protection of an MOV based device. Diodes can easily be destroyed by voltages above their rating which is usually in the hundreds of volts. MOVs however can handle 10000 volts. MOVs however have to be considered sacrificial since their capacity to absorb spikes has a lifetime limit dependent on the voltage and amperage of the surge absorbed. I would guess one would not want to combine the two functions in single circuit package since you would have to throw out the regulator every time the MOV reached it's capacity...
MOV's ➥ http://www.protekdevices.com/pdfFile...Comparison.pdf
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Old 21-01-2010, 11:45   #13
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A simple series pass regulator , like the LM wil not be suitable for what you wnat here as the input voltage is too close to the required output voltage and these devices can have parasitic oscillation when the too get close.

Dave
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Old 21-01-2010, 18:50   #14
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Firstly, thanks to all for the good advice/help.
To clarify a little, what I am trying to do is protect my lighting LED's. The reason for this is that they are not very good quality and although they state on the bulbs '12v -18v', they are Chinese made and from experience this stated voltage range doesn't mean too much. In any event, I think that LED's perform best when they are fed a stable voltage. Until now, what I have done is put two diodes in the positive wire to the lamp. Since diodes have a forward voltage drop of 0.6v, this has had the effect of reducing the voltage to the lamp by 1.2v, giving me a measure of protection in most circumstances when the voltage is up around the 13v + mark. Unfortunately (or fortunately) we are having a pretty windy summer and that windmill of mine is poking 14.4v into my system in the gusts, which is a little bit too much for my diodes (reducing the voltage to 13.2v) and that is a bit too much for my crappy LED's. It is also evident that there is plenty of technology available that will provide a stable 12v, - its just that I'm trying to do it on the cheap! Possible, do you think?
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Old 22-01-2010, 00:18   #15
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Lightbulb I used a different Low Dropout Regulator

I used a Micrel MIC29300-12WU LDO regulator for a similar application, and it seems to be working well enough for me (6 months later). I ordered it from Digikey, and it has a much lower dropout voltage than the one mentioned earlier in this thread. In my application, typically ~300mV @ ~2A draw; absolute MAX spec was 600mV @ max current, 3A) It runs around $5.50 instead of $1.50, but that is still a pretty cheap solution. [Digikey probably had 50 other 12V regulators I could have chosen from. Another one might be better]

I am only using it to power some 12VDC LED ropelight. This doesn't have a good regulator circuit (like most 12V LED fixtures or bulb replacements have); just a current limiting resistor. I have been on the hard for quite a while, and am on shore power, i.e. 13.5V all the time. This did burn out my rope light....I discovered that its brightness was about half of what it started out at within a couple of months.

In my case, this isn't my most power efficient light, so if my battery is running low, I would probably use other lights anyway. If I was afraid that half a volt drop would put me completely in the dark, I would have done something different.

Disclaimer: I did work as an EE in a former life....although this application isn't exactly my speciality. But I do still remember how to read a datasheet.
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