Overvoltage

[off-grid-geeks]

We run our off-grid home on 12 volts DC. All our lighting, fans, pumps, TV, DVD, laptops etc.

Our batteries recommend that the absorb phase be 2.5 volts per cell, so that equals 15 volts.
Equalize is recommended at 2.6 volts per cell, equaling 15.6 volts.

Presently, all of our 12 volt household devices run through a fuse panel tied to the battery bank. So during absorb or equalize, these are rather hot voltages to be feeding our 12 volt devices.

I'm looking for some type of a voltage regulator that will clamp the voltage going to the fuse panel at a nominal 13.2 volts when the charging voltage is higher, and yet feed the actual battery voltage to the panel when the bank is at or lower than an actual 13.2.

Examples:
15.6 => 13.2
14.0 => 13.2
13.2 => 13.2
12.5 => 12.5
11.5 => 11.5

Any suggestions? I'd like a regulator that can handle at least 10 amps, higher would be better.

Thanks!

[boB]

Yes, 12V systems don't always take the semi-high voltages required for flooded lead acid batteries.
A lot of inverters too.

What you are proposing is interesting but if it is actually practical to do most likely depends
on how much current your other 12V devices and appliances require.
The problem is that your battery and your appliances are in parallel which means that
they are at the same voltage.  There are some ways to do this though.

One thing that comes to mind is to add some semi-high current capable diodes in series
between the battery and those devices.  And add a switch across those diodes that can
bypass them when you are not equalizing or Absorbing. Depending on the amount of current
your appliances take, you might need a heat sink for those diodes to keep them cool.

You could also use one of the Classic's Aux outputs so operate a relay that UN-bypasses the
diodes automatically when the battery voltage gets high enough to warrant switching the
diodes back in circuit to give you the voltage drop you need.  Since you will be doing
an absorb cycle more than EQing, I would just drop the 15.0 volts to 13.2 volts or,
a difference of 1.8 volts which would be 2 or 3 diodes in series.

Anyway, that's one possible way to do what you're asking without a lot of hassle, maybe.

What is the current draw of the devices you want to protect ?

boB

[off-grid-geeks]

boB,
The diodes and using the AUX to bypass them is a good idea, thanks.
Our appliance draw is nominally 1.5-2.0 amps (we use very efficient LED 12v lighting and fans etc.). When one of the water pumps kicks in, it can jump to 7-8 amps. So I was thinking 10-15 amps of protection would cover me.

I was also thinking of placing a Buck converter between the battery bank and the fuse panel. What do folks think of this idea, here is one I'm looking at using, its good for 15 amps of output. One advantage of a Buck, besides lowering my battery voltage to safe levels, is that it will also raise the voltage up to 13.2 when the battery is below that voltage.

http://www.amazon.com/dp/B00JCTITZI/ref=wl_it_dp_o_pC_nS_ttl?_encoding=UTF8&colid=336MJUZQ75JGN&coliid=I1I2UT3T5OOQZY

[dgd]

... One advantage of a Buck, besides lowering my battery voltage to safe levels, is that it will also raise the voltage up to 13.2 when the battery is below that voltage.

No it won't
Its only a buck converter so it can only reduce the input voltage to a lower voltage, hence the 1v difference being needed.
It is not a booster where the input voltage can be raised to a higher output voltage
The three series connected power diodes ssr switched by AUX1 is a better idea.

dgd

[off-grid-geeks]

dgd, I beg to differ, but I've used Buck converters before.
Some only boost, some only lower, some do both.

I use one on my 12 volt ceiling fan, it takes 12 volts in and provides a variable output of 9 volts to 30 volts, allowing me to run the fan at variable speeds. It can both lower and boost the input voltage.

[RossW]

dgd, I beg to differ, but I've used Buck converters before.
Some only boost, some only lower, some do both.

dgd is correct, I suspect you're confusing "switched-mode" for "buck".

A buck will always produce a voltage that is lower than the input.
There are a number of boost-buck converters that first boost the voltage, then buck it, to produce a wide range output that includes voltages both above and below the input.

[zoneblue]

Theres a wide range of dc converter technologys. Until recently those that can produce output voltages near their input voltages werent terribly efficient. However, check out these:

http://www.ebay.com/itm/251802879375

The translation on that particular listing leaves a bit to be desired but if you download the datasheet for the chip, the synchronous recitification and single inductor makes these capable of effciencies in the high 90s.

Very cool.

[off-grid-geeks]

dgd is correct, I suspect you're confusing "switched-mode" for "buck".

Okay, then let me get more precise. What I am suggesting it technically called a "Buck-Boost converter".
Most manufacturers of them that I have seen simply shorten the name to "Buck converter", but as the replies I have received indicate, the manufacturers are incorrect in so naming them. They are correctly called "Buck-Boost converters". And this is what I am looking at installing, and what I am asking for feed back on, based on their advantage over the diode solution (which I have as of this evening installed and am testing, thanks boB) in that this device can also boost low battery voltage up to 13.2 volts.

http://en.wikipedia.org/wiki/Buck%E2%80%93boost_converter

[boB]

Yeah, I suppose that converter linked on Amazon is buck only because it says...

Minimum Voltage Difference: 1V

Which, if it was buck-boost would not have that limitation I suppose.

The diodes should work nicely for your LEDs I think.  They shouldn't get very hot either if the current is only a few
amps at most.  No problem !

So what happens if you give the LEDs 15.5 volts I wonder ?  Will they break ?  If there
is any chance then the diodes should help that.

boB

[mike90045]

for LED's - check these guys out.
https://www.wiredco.com/LED_Lighting_Low_Voltage_s/1874.htm
  I like their disc LED's that have the integral driver for 9-30V  I've used a fair number of them over the years, and they work well. 

[RossW]

What I am suggesting it technically called a "Buck-Boost converter".

Correct.

is what I am looking at installing, and what I am asking for feed back on, based on their advantage over the diode solution (which I have as of this evening installed and am testing, thanks boB) in that this device can also boost low battery voltage up to 13.2 volts.

In the power range you're asking for (10A), there are few buck converters that'll make more than low-90's% conversion efficiency. The same sort of efficiency for a boost. Lets say 93% for arguments sake.

You will get roughly 93% of 93% out what you put in, or 86% out. So at 15V in, to get 12V out @ 10A will take 12*10 = 120W out / 86% = 140W input required.
At 15V thats 9.33A

If you put three power diodes in series with your 15V battery, you'd get 13.2V out (near enough), and at 10A you would be blowing 18W as heat across your diodes.

So at 15V, 3 diodes is marginally more efficient than a boost+buck double conversion.

At higher voltages, the buck+boost comes out further ahead.
At lower voltages however, the diodes come out better off... and if you were happy with no diodes at say, 13V you would have zero losses - whereas the boost+buck will STILL be wasting 20W of your power.

(Assumes both conversions are 93% efficient. I doubt you will achieve anything close to that under all conditions)

[ClassicCrazy]

Thanks for the mathematical explanation Ross. That helps understand the comparison of the two voltage stabilization methods .

[zoneblue]

That unit i linked to is not a boost then buck unit. Its  a 4 mosfet thing that runs in one of three modes depending on the input/output voltages. Very efficient. 10 amps. Tiny heatsink.

[dgd]

Ogg, so how did the three diodes voltage limiter work? Did you get aux1 via an SSR to automatically control inserting them into circuit?
I had a closer look at some of my 12v led lighting, they use a 3w led mounted on what appears to be heat sink and there is some constant voltage supply device below it. Mine worked from 10v to 16v dc input with Jo change in brightness.

Dgd

[off-grid-geeks]

Ogg, so how did the three diodes voltage limiter work? Did you get aux1 via an SSR to automatically control inserting them into circuit?

Yep, worked just fine. Used NC relay and AUX1 in 'Diversion' mode.