120VDC for off grid power

[BruceM]

SteveU requested that I start this separate thread.  Here's the post from another battery thread:

"I love my 120VDC system with cheap Walmart 12V marine batteries, using individual battery shunt regulators. (A scheme developed my Manzanita Power for electric cars with AGM batteries.) There's virtually no water loss, no need for protracted equalization, and a premature death in the 3rd year can be replaced without having to worry about age matching.  (My 2 battery losses were both due to prototype hardware failures due to corrosion on unsealed boards with too fine a clearance around traces.)  At the end of 4 years, the charge efficiency was noticeably poor, so I retired the whole set when I had a cell loss last fall. I'm too lazy to work hard to save an aged $67 battery.  Twice a year I check all the cells SG, and add water.  I'm ready to go to once a year now; I'm not adding hardly any water, and have had almost no variation in water consumption between cells or batteries.  I do mini-equalization charges (2 hours) monthly.  The Manazanita Power approach to charging long series strings is a real winner in my book.  I realize I'm well outside the mainstream with 120VDC, but someday this will be much more common, unless the battery technology picture changes."

You can read more about Manzanita's strategy for charging high voltage strings of lead acid batteries here:
http://www.manzanitamicro.com/products?page=shop.product_details&flypage=flypage.tpl&product_id=87&category_id=22

The manual is downloadable and has more good information.

I use a similar strategy, but with PV charging knowing when the batteries are full requires a bit more thought, due to such things as a passing cloud. My battery regulators are analog, and limit the battery voltage to one of three selected temperature compensated voltages, float, bulk charge, and equalize. Two bits of output from the PicAxe battery bank charge controller (BBCC) selects which voltage all the battery regulators see via their opto isolators. Feedback to the PicAxe is a single analog signal from each of the ten battery regulators (an opto-isolated analog signal) proportional to the amount of current the battery regulator is shunting in order to maintain the selected voltage.  The BBCC also reads PV charge, Load, and AC charge currents, and controls an analog PV charge controller
which regulates my 875 watt PV array (120VDC nominal) to charging at either full power, 2.5, or 0.5 amps of net charge.  The PV charge regulator is a small board mounted on a big aluminum heat sink.  

I don't do pulsed regulation despite the small size and efficiency because my epilepsy is aggravated by high frequency EMI.  Even the micropower processor is in a shielded enclosure with filtered connectors; a 1200 baud signal is the fastest that can be used.  So in general my design would not be something the general public is interested in.  

I've found 120VDC to be very handy.  Most switching supplies will work fine, and universal motors without triac speed controls will work fine.  There's a nice RV park type diaphram pump that works on 120VDC.  My entire low power computing system and rear projection display all use stock supplies.  I have to filter the heck out of them to keep the 120VDC clean, and the house power is separately filtered with a military grade, Filtron -120dB filter (RFIcorp).

I use no AC except for washing machine and water well pump, and (rarely) some AC tools for the shop.  My wood shop and hand tools are all pneumatic, as I can't work near AC motors. I run my Listeroid 6/1 to pump air to a 500 gallon receiver and to do run an AC washer plus pump water from my well (1/2 hp submersible pumping from 200 ft).  I have 12psi via gravity feed, which is perfectly adequate with oversized pipes.  I use a propane refrigerator modified to be sealed combustion and have a Peerless propane range modified to be piezo start.  All my lighting is 120VDC incandescent and halogen, as I don't tolerate the EMI from any of the new lighting, and can't tolerate the light quality (spectrum) of fluorescent lights of any kind (including the phosphor based white LEDs).  Someday I'd like to experiment with RGB LED lighting, to see if a custom panel array of LEDs might be useable.  But the heat loss of the incandescents is NOT a loss for me in the winter, when I use the most lighting, and at 25 cents a bulb they are hard to beat.

[BruceM]

Here's some photos of the simple analog battery shunt regulators I designed, and PV analog charge controller.

[deeiche]

thanks for your detailed post.

Since you do a lot with pneumatics have you ever looked at a Brumby Pump?

[SteveU.]

Deleted. S.U.

[BruceM]

Hi Deeiche,
There is a similar pneumatic pump sold in the US, typically with a wind driven, modified air compressor.  I looked into them before I built my off grid homestead. They are popular in windy western US states for stock watering.  Alas, the compressor must use a synthetic oil which of course ends up as a vapor in the air to a small extent, and they have not been approved for potable water because of the water contamination with oil vapor. I sure liked the simplicity and durability of the well pump, though!

SteveU, I had an nice building inspector who was a competent electrician, and he respected my knowledge and care in doing DC safely.  I skipped the final inspection as I didn't care to do smoke detectors (which I refuse to use due to epilepsy) and GFI outlets and such. He might have passed me anyway but I didn't want to put him on the spot or strain our friendship.

There is a lot more known about higher voltage DC safety now because of it's growing use in computer data centers.  120VDC is actually much less painful and less of a risk than 120VAC. It feels more like a static discharge.  I'd much rather work in a hot box with 120VDC myself. AC HURTS.  There are some good technical papers on computer data centers use of DC, but this is a more popular, less technical article:

http://www.scientificamerican.com/article.cfm?id=edisons-revenge-will-direct-current-make-a-comeback-in-us


Switches are a bit of a problem for 120VDC as the current gets to 1 amp or more. Typical AC light switches will arc and melt on the first "off".  I used some now discontinued Cooper 150VDC rated snap type light switches for my house.  There are work arounds via MOSFET assisted switches and also I did find some heavy duty AC switches that worked well, but have also been discontinued.  Lamp switches and rotary cord lamp switches are not a problem, since those were originally designed for Edison's 110VDC system. IXYS makes a 200V P-channel mosfet which I use for simple solid state switching of the +120V.  My system is negative ground for safety in changing bulbs and such where the AC neutral connection is typically not very well protected.  I did seriously consider a center grounded system (+-60V), but ultimately decided Edison's approach was best.

On another thread here, someone listed their 24/7 parasitic loads from GFIs, arc detecting breakers, and inverter. They exceeded my winter DC incandescent lighting use.  I'm still fuming over f'ing Phillips Lighting's light bulb bill. By the end of the year the PAR type halogen spot and flood lamps will be discontinued.  I use them for my homebrew SAD light, so now I must buy lifetime spares for that, too.  Grrr. 

[quinnf]

Oh wow, it's deja-vu all over again.  The Tesla-Edison debate from 100 years ago:

https://en.wikipedia.org/wiki/War_of_Currents

q.

[mobile_bob]

Bruce has more fuzz on his balls than i do!

lol, 

i can tell you that working with 48volts and holding a hot lead while allowing the back of your forearm to contact a ground will damn sure get your attention, in a hurry!

120 vdc will certainly knock the living crap out of you.

at least 120vac turns loose  of you 120 times per second, 120 dc on the other hand, if it gets a hold of you it won't let go.

of course this does not mean you can't work with or use it safely, just that one needs to give it the respect that is due, of course one ought to have a healthy respect for 120AC too.

more folks get killed each year with 120vac than do those that get tangled with 240vac, so under the right conditions 120 vac can get ahold of you and hang on too.

the only other concern i have with higher voltage battery strings comes when you have an aging bank, if one of the cells boils dry and starts gassing hard, and there is an internal short or spark, things get really exciting in a hurry!  therefore any high voltage string ought to be contained in some sort of steel containment in my opinion... or at least in a non habitated building built of fire proof materials.. even then maybe some sort of shielding might be prudent.

i have seen first hand what happens when a cell shorts in a high voltage string,  from the after math i know full well i would not want to be anywhere around such a failure.

the instantaneous power available is mind boggling indeed, a reasonable size bank can produce a couple hundred amps without breaking a sweat, so... 120 vdc x  200 amps= 24kwatts  certainly enough to flash a quarter inch bolt like a flash cube!

judging from the hole pierced in three plates of steel about the size of a quarter, my guess the sound was like a 12 gauge shotgun blast. that being a shorted cell in a 240vdc string.

probably not a likely occurrence, but something to keep in mind as within the realm of possibility.

bob g

[deeiche]

Hi Deeiche,
There is a similar pneumatic pump sold in the US, typically with a wind driven, modified air compressor.  I looked into them before I built my off grid homestead. They are popular in windy western US states for stock watering.  Alas, the compressor must use a synthetic oil which of course ends up as a vapor in the air to a small extent, and they have not been approved for potable water because of the water contamination with oil vapor. I sure liked the simplicity and durability of the well pump, though!
SNIP

I figured you looked into them.  I did not know about the non-potable water, I did not see anything about only using it for non-potable use.  However looking at the design there is no discharge airline above ground.

thanks for the reply.

[BruceM]

There has been more research and assessment on DC safety due to the advent of it's use for Computer Data Centers.  Around 350VDC is popular, to keep stock switching supplies designed for 240VAC happy.

Edison chose 110VDC as a good compromise for safety and distribution for his lighting systems.  Still just about right for my purposes.  Edison lit a lot of homes for quite a while, and people were not dropping like flies, despite a much poorer quality of wiring (post and knob), etc.  It was much safer than the gas lighting of that era.

The "can't let go" story is one I was also concerned about.  It's not born out in the safety research. For killing you by stopping your heart,  DC is safer by quite a voltage margin.

If you look at who the players are in the move to DC data centers, you'll see big corporation names like Intel and big universities like UC San Diego.

http://www.vde.com/en/dke/dkework/newsfromthecommittees/2011/documents/2%203%201.pdf

Explosion of batteries from spark ignition of Brown's Gas can happen regardless of battery bank voltage, and is why some counties now insist that battery banks not be located in the home.

Even 48VDC can kill you dead, so thinking safety first around DC or AC power is always important.

[mobile_bob]

Bruce, all good points!

my only concern relates to getting complacent with battery strings in higher voltage systems.

(i know you are not among that group)

i just get a bit concerned when i see large battery strings sitting unguarded just waiting for someone to
bump up against them, and not having any shielding to prevent contact or contain a massive short circuit fault.

most folks would never consider having exposed buss bars with 120/240, but many think nothing of having open exposure to a high voltage DC buss.

both should be shielded well in my opinion.

a couple years back i put together a 192vdc string to test an inverter/ups system,,, thankfully the inverter did not work, so i could dismantle the string and not be tempted to use it without all due precautions.

back when i was in business i frequently worked on 480vac three phase systems, and of course they are well shielded and you learn to keep on hand either behind you or in your pocket at all times... somehow i felt ok when working around that stuff....

however that 192volt string scared the living crap out of me!  too many battery posts sitting exposed
and just waiting for me to make a mistake or drop a wrench.

as you state, done correctly there is no real difference between the two, AC or DC, done wrong and carelessly, both can and will kill you.


bob g

[SteveU.]

Hmmm.
Well, this is not good.
BruceM you were correct. We should direct discuss this. I'll see if I can get the other guy using/doing directly involved.
You and I are both moderators here. Moderators supposed to dampen down the static  - not create it.
I like it here and have no intention of windspitting this issue.
I am deleting out my comment and thanking you for trying. Up to you whether you leave yours up or delete the thread. You've got some personal detailed in there.
I will message you and see if the other guy will get involved.

FWIW 150-300VDC hybrid vehicles are out their in service for 10 years now. I serviced and study trined on some of these now. EMT reponders and body shop people been dealing with these all mashed up for just as long. Yep takes special training and concern. Seen all of the new intercity transit busses? Exposure to High voltage battery banked multi-KW pushed DC power is not going away. It is increased WAY past the 70's, 80's DYI'er up to 90 VDC with a pick-up bed bank of batteries usage.

Could say more. But wife's day and I AM NOT SUPPOSED TO BE KEYBOARDING AT ALL.

Regards
Steve Unruh

[BruceM]

No worries, Steve.

As you point out, higher voltage DC is already growing rapidly and will be much more common, in the near future. We'll all have more chances to be able to get comfortable with it. 

[mobile_bob]

i hope i haven't been the rain on the parade guy, it is not my intention at all.

it might well be my fear of high voltage dc comes on the heals of 40 plus years of dc meaning
a 12volt battery source, and rarely a 24volt source... while either can throw a lot of sparks it is not likely to kill me... this leads to complacency on my part..

something in the back of my brain just seems to automatically discount the danger of higher voltages when my eyes see a battery, so i have to force myself to stop and think, whereas i always stop and think before i go poking around an AC panel.

now this might not be the case for everyone, or for that matter even the majority of diy'ers..

it is my shortcoming and i might well be projecting this on others.

so in short i am not discounting the use of 120vdc, if it is handled no differently than 120vac, or rather viewed no more or no less dangerous than the other, then all is fine.

apart from just being cognizant of the dangers associated with batteries in general, that is something to worry about no matter if it is a 12volt string or a 120volt string, either one can blow up given the right circumstances... one should just consider the fact that batteries are a necessary evil and a fact of life, so just build systems that are safe and practical.

again it was never my intention to discount the use of a high voltage dc system...

bob g