Author Topic: Battery bus design  (Read 10436 times)

0 Members and 1 Guest are viewing this topic.

Offline ksouers

  • Full Member
  • ***
  • Posts: 126
  • Karma: +6/-0
  • Missouri, USA
Re: Battery bus design
« Reply #15 on: April 29, 2012, 12:46:04 PM »
I'm a little concerned you are planning on continuously growing your bank. It can be done, but you're typically better off starting with a larger bank, rather than having an arrangement of young and older batteries.

Rover

Well, probably not grow continuously, but fairly quickly. When I get the bank up to where I want (about 650 AHr @ 24 volts by the end of July) they will all be less than 6 months of each other. That'll be about the limit I have for space to mount panels. The older group 27 batteries will be taken out of the bank before then and just used for camping and boating.

Now, if my wife decides she really does want that small farmstead she's been talking about then all bets are off. I will be heading off grid! But that's a very long shot and wouldn't place that bet. She's too much of a big city girl.

I looked at Speedy Metals a year or so ago, they seemed a little pricey compared to who I usually use, Online Metals, at least for the grades I wanted at the time. McMaster-Carr seems to have the best price for tool steels, kind of hit-and-miss on other metals.

Kevin
As far from the city as I can get but still keep my job.

Offline Rover

  • Full Member
  • ***
  • Posts: 192
  • Karma: +7/-1
Re: Battery bus design
« Reply #16 on: April 29, 2012, 01:06:53 PM »
I know this may sound hard, but consider the following. (I'm not assuming this is your plan)

You already have a plan and an end goal. Maybe finances preclude you from doing the one time everything at once.

I've been there, done that. Solar panels etc can be bought without worry at any time. But I'm very reluctant to see a battery bank built with batteries that some have already been in service, maybe even mixed with non matching types and ages. I've killed young and old batteries with that approach.

My opinion, buy the bank in one shot, or as close to age as possible. Try not to put part in service then add to it. Definitely do not mix battery types for an extended time.

I know you state that they will be within 6 months of each other. Stuff happens.. and that 6 months can end up being a year, for a whole host of reasons.. no money, other activities interfere, batteries not available... etc.

You probably already have thought all this out, I'm just posting for anyone else :)

Rover



Rover
Location: South East Virginia US

(Where did I bury that microcontroller?)

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Battery bus design
« Reply #17 on: April 29, 2012, 03:18:15 PM »
$9000 was the high estimate we got for a small genny with autostart, installation, natural gas service upgrade and transfer panel.

Are you sure you want a natural gas genset?  In a disaster, natural gas is one of the things that stops working because it takes utility power to pressurize the lines at the pumping stations.  A few of the interstate lines have natural gas pumping engines.  But most of the local infrastructure is pressured by electricity with motors.

We got a Generac EcoGen LP genset:
http://www.generac.com/Residential/EcoGen_Series/Product/6kW/

It can run for 400 hours (almost two years for us) on 450 gallons of LPG.  The only downside to the LP genset is that it refuses to start much below zero F.  So we also have a gasoline-fueled 3 kW Champion Power Equipment backup genset - also auto-start.  The Champion started last winter at -32F with no pre-heat.

The EcoGen is about $4,000.

If you have a decent inverter/charger with gen support, you do not need a genset capable of running your whole house.  If you have Outback or other cheaper inverters that do not have gen support, then you will need a larger genset.  Inverters with gen support are able to "blend" generator output with inverter output so your total capacity is the sum of both the genset and the inverter(s).

Spending $9 Grand on a standby gen is ridiculous.  If you are dead set on spending $9 Grand then buy a Xantrex XW (has gen support) and a smaller generator instead.
--
Chris

Offline ksouers

  • Full Member
  • ***
  • Posts: 126
  • Karma: +6/-0
  • Missouri, USA
Re: Battery bus design
« Reply #18 on: April 29, 2012, 06:00:35 PM »
Chris, the decision was made to nix the standby genset and go with RE, but still keep the manual gasoline genny as backup at least for now. I may swap that out for an electric start some day, even better if it has autostart. I'm getting too old to yank on a cord anymore :)

The plan is to go with an Outback inverter when I switch over to a 24 volt bank. I won' t be off grid, just powering a few things around the house. But it has to be ready to be pressed into service as backup power for the house when the grid goes down. If I happen to knock $10 or $15 a month off the electric bill by using less, that's just gravy.

The bids we got were between 6 and 9,000 for complete installation. We decided to spend the $6,000 on solar especially in light of the debacle we had a couple years ago getting trapped with no way to refuel the genny. I figure with the RE we can stretch that 20 gallons of gas out for many days as long we get some sun. Running a fridge, a microwave, the furnace and coffee pot shouldn't be too taxing on the system I have in mind.


Kevin
As far from the city as I can get but still keep my job.

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Battery bus design
« Reply #19 on: April 29, 2012, 06:29:33 PM »
We decided to spend the $6,000 on solar

I'm breathing a sigh of relief.  Your money is MUCH better spent on them solar panels than a freaking generator.  Like Glen said, you can probably just get by with a $500 generator.  When people start talking about spending $9 Grand on a residential standby generator, I'm like, WTF you got?  A 50 room mansion?    :o

Businesses, factories, etc. - $9 Grand is a little generator.  In fact, a tiny generator.  But for a home, and the needs that most people have in the event of a power outage, $3 -4,000 is a good price for a capable 14 kW standby generator.
--
Chris

Offline rossw

  • Senior Moderator
  • Hero Member
  • *******
  • Posts: 790
  • Karma: +27/-0
  • Grumpy-old-Unix-Admin
Re: Battery bus design
« Reply #20 on: April 29, 2012, 06:35:31 PM »
I figure with the RE we can stretch that 20 gallons of gas out for many days as long we get some sun. Running a fridge, a microwave, the furnace and coffee pot shouldn't be too taxing on the system I have in mind.

Long time since I used an electric coffee pot, but don't they draw quite a lot?

Years ago I got (as an emergency backup) a little camping grill type thing. A single gas burner, runs on a can of butane. One can lasts a surprisingly long time - and cans were about 50c each, store easily and should last in storage forever and a day. Sure, it's not renewable - but it'd sure stretch your RE electric resources. The whole thing - burner, carry case and a couple of cans of gas cost me $5 or $6 brand new from one of the cheapy "reject" style stores. Might be worth having on hand too.

Offline ksouers

  • Full Member
  • ***
  • Posts: 126
  • Karma: +6/-0
  • Missouri, USA
Re: Battery bus design
« Reply #21 on: April 29, 2012, 06:45:53 PM »
I figure with the RE we can stretch that 20 gallons of gas out for many days as long we get some sun. Running a fridge, a microwave, the furnace and coffee pot shouldn't be too taxing on the system I have in mind.

Long time since I used an electric coffee pot, but don't they draw quite a lot?

Years ago I got (as an emergency backup) a little camping grill type thing. A single gas burner, runs on a can of butane. One can lasts a surprisingly long time - and cans were about 50c each, store easily and should last in storage forever and a day. Sure, it's not renewable - but it'd sure stretch your RE electric resources. The whole thing - burner, carry case and a couple of cans of gas cost me $5 or $6 brand new from one of the cheapy "reject" style stores. Might be worth having on hand too.

Hi Ross,
Yes, they do draw quite a bit, about 600 watts. But it's only for a few minutes while the pot is brewing, when done I grab a cup and the rest goes into a thermos and the the machine is turned off. Sterno is also cheap if one were to go that route. The microwave also draws a lot but for a short time so It's not too bad as long as long as you don't over do it. Can of soup is done in a minute, cold cut sandwich, yum.

As long as the furnace pumps out heat and the beer stays cold I can live on that for weeks.


Kevin
As far from the city as I can get but still keep my job.

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Battery bus design
« Reply #22 on: April 29, 2012, 07:42:20 PM »
Long time since I used an electric coffee pot, but don't they draw quite a lot?

We brew fresh coffee for breakfast every morning.  Our coffee maker draws about 1,200 watts while it's brewing.  Then it drops to about 250-300 watts intermittent while the heating plate cycles on and off to keep the pot hot.  So they're not really that bad.
--
Chris

Offline ghurd

  • Global Moderator
  • Sr. Member
  • ******
  • Posts: 442
  • Karma: +22/-0
    • GHurd Solar
Re: Battery bus design
« Reply #23 on: April 29, 2012, 08:49:19 PM »
Years ago...  runs on a can of butane.... cans were about 50c each...

That must have been MANY years ago!
6~8 years ago it was retailing for like $6~8 a can?
A ma&pa dollar store up the road had it for $2 a can, and I'd get all they had to take to a store 45 miles away to sell it for $3 a can, and they'd sell it FAST for $5 a can.

Might be different Down Under, but the US has ALL kinds of rules about shipping that kind of thing, and it got worse after 9-11.  The price went through the roof after 9-11.


I agree with Chris about coffee pots, mostly.
Not sure about the one I use now (has more damn buttons than a laptop).
The one 2 or 3 ago was like 600W or <1W.  It only had 1 heating element.
When brewing it was a high duty cycle.  Then the duty cycle was a lot less to maintain a hot pot.
The Average Power may have been only 50W, but a 100W inverter was not going to make it work. LOL


How I was thinking about a genny is like I usually think in this kind of situation.
The battery bank is USUALLY big enough to supply adequate power in an emergency, right?
And the bank, with RE input, is often enough to deal with an emergency, right?

I am thinking a lawn mower motor and DC genny is going to use a lot less gas for the same results (warm house and cold beer).
I know a guy who put a PMA on an old 3 or 4 HP rototiller engine, and had a hard time keeping it below 300W(?) at idle.

"We went through 20 gallons of gas in two days" ?
That is EXACTLLY what I am talking about.
Try to burn that much gas with a decent 3.5HP B&S lawn mower engine.
No reason to burn that much fuel except to keep the motor at 3600RPM and the output frequency at 60HZ, but the inverter keeps the frequency at 60HZ even if the motor is NOT running!

G-

Offline ChrisOlson

  • Hero Member
  • *****
  • Posts: 510
  • Karma: +29/-5
  • just trying to survive
Re: Battery bus design
« Reply #24 on: April 29, 2012, 10:32:52 PM »
I am thinking a lawn mower motor and DC genny is going to use a lot less gas for the same results (warm house and cold beer).
I know a guy who put a PMA on an old 3 or 4 HP rototiller engine, and had a hard time keeping it below 300W(?) at idle.

That's what I'd do too.  Back when we used to run short on power all the time I put a little Delco 10SI on a Tecumseh 6hp snowblower engine:
ila_rendered

In the evenings I'd start the thing and let it run just above idle, about 2,000 rpm, and it would keep the bank up with our heavier evening time loads on before we went to bed.  It would put out 20 amps @ 14 volts on about 1 pint of gas per hour.  Later on when we went to 24 volt system I swapped out the rotor in it with a 24 volt rotor.  I used the stock stator in it, and full-fielded the rotor by grounding the regulator tab.  Never changed the regulator either.  But the rotor had to be changed because the 12 volt rotor would burn out full-fielded on 24 volt.  On 24 volt it would put out the same 20 amps @ 2,000 rpm.  But it made the engine work a lot harder so it burned more gas - almost twice as much.

After we bought our big battery bank I've never used it anymore because it can't put out enough power to amount to peeing in the ocean to charge our bank anymore.  But I put a LOT of hours on that thing over the years without dumping much gas in it when we didn't have the battery capacity we needed.

No reason to burn that much fuel except to keep the motor at 3600RPM and the output frequency at 60HZ, but the inverter keeps the frequency at 60HZ even if the motor is NOT running!

Glen makes a good point about 60Hz AC generators here.  When you buy one to power your house for power outages the usual recommendation is to size the generator so it runs at 50% load carrying your normal loads so it has reserve for surge loads.

For off-grid it's different.  You size your battery bank, inverter chargers and generator so that when the gen comes online it runs at full load.  Example: our battery bank is 2,400 amp-hours @ 24 volt nominal.  The bank likes 10% of the amp hour rating for bulk charging, which is 240 amps.  Our inverters put out 120 amps each and our 6 kW generator can deliver enough power to run the inverter chargers at the full 240 amps during initial bulk charging when it comes online.  There is no "reserve" for surge loads, but we don't need it with a battery/inverter system because if a heavy surge load comes on during charging the inverters take over and cut the amount of amps the chargers are taking from the generator to prevent gen overload.

People who just have grid power with a standby generator don't have that luxury so the generator has to be sized different (much larger).

60Hz generators are most efficient (kWh/unit fuel) at full load.  They are least efficient at zero load.
--
Chris

Offline rossw

  • Senior Moderator
  • Hero Member
  • *******
  • Posts: 790
  • Karma: +27/-0
  • Grumpy-old-Unix-Admin
Re: Battery bus design
« Reply #25 on: April 29, 2012, 10:38:23 PM »
Years ago...  runs on a can of butane.... cans were about 50c each...

That must have been MANY years ago!
6~8 years ago it was retailing for like $6~8 a can?
A ma&pa dollar store up the road had it for $2 a can, and I'd get all they had to take to a store 45 miles away to sell it for $3 a can, and they'd sell it FAST for $5 a can.

Might be different Down Under, but the US has ALL kinds of rules about shipping that kind of thing, and it got worse after 9-11.  The price went through the roof after 9-11.

It was while we were building our new place - so in the last 6 years or so.
One of the guys working here had one, and on those bitterly cold days, a hot lunch was a great idea.

I just went looking, and yes, they've gone up.
8oz cannisters are now $15.20 for a 12-pack from amazon.com. http://tinyurl.com/cmyprtz
 Thats $1.25/can. And yes, there are restrictions on posting them. I'm sure I saw them selling locally at the reject shop here for under $1/can recently. Ahh, "progress". *sigh*.

And Amazon have the little cooker still listed, more than I paid - for $11.78 for the "deluxe" version.
http://tinyurl.com/8xljgsa



Offline ghurd

  • Global Moderator
  • Sr. Member
  • ******
  • Posts: 442
  • Karma: +22/-0
    • GHurd Solar
Re: Battery bus design
« Reply #26 on: April 30, 2012, 11:01:46 AM »
Those are much smaller cans, but a lot cheaper per ounce!
$15.20 + $16.75 shipping.  LOL
G-

Offline ksouers

  • Full Member
  • ***
  • Posts: 126
  • Karma: +6/-0
  • Missouri, USA
Re: Battery bus design
« Reply #27 on: April 30, 2012, 05:42:18 PM »
"We went through 20 gallons of gas in two days" ?
That is EXACTLLY what I am talking about.
Try to burn that much gas with a decent 3.5HP B&S lawn mower engine.
No reason to burn that much fuel except to keep the motor at 3600RPM and the output frequency at 60HZ, but the inverter keeps the frequency at 60HZ even if the motor is NOT running!

G-

G-
I should mention that was the first time we used the genny under emergency conditions. It was purchased shortly after a summer storm had taken out half the power in St Louis county and about a third of neighboring St Charles county. I admit I could have done a much better job of fuel and power management and probably stretched that much gas out for at least 3 and possibly 4 or more days. I had no method to hook into the house wiring, hadn't even thought of it. Extension cords were stretched out all over the house. We were running 2 1500 watt space heaters, fridge, lights etc and I was trying to keep an aquarium full of saltwater fish alive. I had the genny running full time. Of course, I had no RE system at the house at the time, either. Not even a spare battery anywhere and my only solar panel was on the boat 40 miles away.

Since that time we have only lost power twice, and only for a couple hours each. We are overdue.

Kevin
As far from the city as I can get but still keep my job.

Offline RichHagen

  • Jr. Member
  • **
  • Posts: 41
  • Karma: +6/-0
Re: Battery bus design
« Reply #28 on: May 02, 2012, 09:11:14 PM »
In my 48V setup, I just took a couple of approximately 24 inch 1 inch by 1/4 inch 6061 aluminum bars and drilled and tapped 10/32 holes every inch or so, staggering them 1/4 inch from the edge from the top with the next 1/4 inch from the bottom as they are mounted horizontal.  The ends and middle have 1/4 inch holes which also serve as mounting points, with the inverter attached at one end.  Smaller stuff is attached to the 10/32 brass binding screws I put in all of the tapped holes.  I have a small cnc, so it was easy to make.  I had originally planned for copper, but did not have it in hand when the need arose, so I programmed the drill template and made one out of aluminum in the interim.  I ordered up the copper, probably from online metals or speedy up in Wisconsin, but it is sitting for now, as the aluminum one, with the Noalox antioxidant grease on every connection has performed flawlessly thus far, and of course cost only a tiny fraction of what the copper would for the same resistance level.  For a permanent installation I would still prefer the copper bus bar as it has lower overall resistance per unit of cross section and fewer oxidation issues if using similar copper conductors or leads, but aluminum is far cheaper and in my case (as well as many breaker boxes and other commercial products) is working out fine thus far.  I think I would have more concern if it was in an area with more humidity or condensation, or a marine environment, but I have not seen any corrosion whatsoever on my aluminum bus bars thus far and have had zero problems with them.  Rich
A Joule saved is a Joule made

Offline rossw

  • Senior Moderator
  • Hero Member
  • *******
  • Posts: 790
  • Karma: +27/-0
  • Grumpy-old-Unix-Admin
Re: Battery bus design
« Reply #29 on: May 02, 2012, 09:28:11 PM »
but I have not seen any corrosion whatsoever on my aluminum bus bars thus far and have had zero problems with them.

I guess everyones experience is different.

In my original setup, I used Aluminium for the interconnects between 48, 2V cells.


There were a few of them:


I was quite pleased with my handywork.... but they required almost constant attention.
They would come lose for no apparent reason, they got warm, they oxidised....

After the tradespeople destroyed that bank (a whole other story), and I had to make a temporary string out of other cells, I initially used Aluminium bar and it was a total disaster. They needed tightening every few days, they ran quite warm to the touch.... and I couldn't replace them quickly enough with copper.


After that - I never had to touch them again.

And when I got more of the AGM cells, I went straight to copper interconnects and they've given me zero problems.