Hybred System Questions

[LowGear]

Admin's "mini microcogen multifunction unit" thread got me to thinking about a problem I have at my winter palace.  I can barely fart without the electric company holding my hand.  And when the weathers bad; no water nor heat is "Terribly inconvenient old thing."
   
The furnace is a Becket diesel powered hot water system.  The well pump is a 1/2 or 3/4 HP 240 volt submersed unit.  Here are my questions. 

1.)  How big of battery pack would I need to get both of these units up and running at the same time?

2.)  How many hours could I expect it to work without a backup generator?

3.)  Is there such a thing as a small QUIET diesel generator that would be suitable for this application?

4.)  Are there SOM units available for question #3?

5.)  Would you hard wire the battery pack unit into the two appliances to keep them exercised or just have a wall switch?

6.)  Alternative solutions?

If you offer information please specify as to "I think" vs "I have witnessed".

Casey

[mbryner]

Hi Casey,

At least I can sort of answer the first question.  Starting the pump has more to do with the inverter than the batteries.  Unless the well pump is a very soft start like a Grundfos SQ series, the surge load is the killer.  Can be multiple times the running amps.  i.e. A 1hp pump that normally draws 8 amps could have a startup surge of up to 40 amps for a fraction of a second.  So you'd have to oversize the inverter, which is where the expense comes in.  

As far as battery bank, that depends on how long you want to run the pump each time.  

For instance: two L16 batteries (6 V, 350 Amp-hr) in series will have 4200 watt-hr of energy.  
2 x 6 V x 350 Amp-hr = 4200

A 1 HP pump = 750 watts while running, correct?  
4200 watt-hr / 750 watts = 5.6 hr until complete discharge.  

Therefore: approx 2 hours of runtime at 50% depth of discharge with some losses thrown in.  Assuming your diesel hot water system has some electrical components, so if you know how many Amps, you can add that into the equation.   I convert to watts to make it easier between DC and AC.

That's the math.  Don't know if that passes your "I think" or "I have witnessed" test.   I have an off-grid system and that's how I do the calcs.

Marcus

[mbryner]

And here's a link explanation on well pumps with inverters:

http://homepower.com/article/?file=HP98_pg140_QandA_4

So, "I think" I answered your first 2 questions. 

[Ronmar]

That well pump is going to be a problem, and going to require a generator of some size to start reliably.  Perhaps 4KW at teh smallest, just for the startup loads.  The same problem would apply to an inverter, and perhaps even moreso, as it dosn't have the advantage of spinning mass to help deal with the inductive startup surge.  I am guessing that this well pump is both lift and pressurization?  If so, it may be possible to drastically reduce it's startup demand by completely removing the pressure at startup, and having it feed water into a larger holding tank at no pressure.  You could then draw from the holding tank to pressurize your domestic water system with a much smaller pressure only demand pump.  This could ultimatly lead to you putting in a much smaller well pump, that runs longer feeding the storage tank, which is how people with low flow wells do it.  Sadly, an inverter to provide for the intermittent load of your pump is going to probably be way overkill for your other demands, and very expensive...

As for battery loading, watts are watts regardless of the source.  Say your well pump when running, needs a killowatt.  Well at 240 VAC, that is 4.17A, at 24V it is 41.7A, plus the conversion loss of the inverter, probably abnout 10-15% best case, so about 47A...

In order to answer some of your questions more specific than that, we need to know the specifics of your demand/load.

Alternatives?  There are probably loads, but that depends on what you are willing to spend, or put up with:)

[mobile_bob]

with a dpdt relay, and a little effort you can setup a system that does not allow both to start and run at the same time.

i would give priority to the furnace/boiler however because it ought to be allowed to finish what it is doing without interruption
i suspect/think/feel, so as not to run the risk of overheating the burner because it was not allowed to finish a cycle, however
i am not sure what you have there, so that may not be an issue.

sizing a system to handle an event that can be avoided without much if any sacrifice in utility seems like a spendy proposition.

then you need to know two things,

1. what is the combined power draw with both loads running?  this will tell you the very minimum inverter capacity you will need

2. what is the starting current of the heaviest load?  and how long does it last? this will give you another piece of the equation

for instance, the well pump draws 10amps running and the furnace draws 5 amps running, therefore you need an inverter with at least
the capability to produce 15amps, however i would suggest upsizing by a third, so figure an inverter that can deliver 20amps continuous.

now if the well pump needs a surge of 30amps, and it is wants to start with the furnace running you will need an inverter with at least 35amps
surge capacity, however i would also upsize that by 50%,  for a total of about 50amps surge.

so you would need an inverter capable of supplying 20amps continuous and 50amps surge, hmmm
good inverters can do twice the continuous rating for surge, so we need 20amps running but twice that is only 40amps surge.

therefore we ought to go for an inverter that is capable of 25amps continuous and rated at twice that (50amps) surge.

this will give us enough head space to get the job done, and also do it within what is likely to be the most efficient part of the efficiency curve.

*all the above numbers are fictional, ymmv, and the inverter you choose may have 1.5x, 2.0x, 2.2x, 2.5x surge capacity, so pay good attention to the manufactures specs here.

btw, the pump manufacture can supply you with running amps (FLA) and starting amps (LRA), as can the manufacture of the oil burner unit
so i would start with them, and use their numbers, because they are likely close enough, however check your utility line voltages and have them
handy for the manufactures engineering dept before you call them. armed with the line voltage spec's they can give you very accurate amperage
and/or wattage.  also be sure to ask them what the power factor of their pump or burner is, because if it is much off unity we have to do another layer of
calc's. most modern stuff seems to have pretty good power factor these days so this may not be much of an issue.  be sure to ask though.

if the power factor is 0.9 or better the above methods of calc's with the suggested uprating will likely work out just fine, if on the other hand the pump
has a power factor of 0.75 or worse, then we need to probably do a bit more uprating on the inverter.

battery sizing?

that is a good question, but first one of my own,  do you have solar panels to charge them or will the genset be the only recharge source?

if you have solar panels there are tons of resources to aid you in determining battery sizing, if however you are going with a genset charger, then
i would present the following.

any time you change from or go through another layer of conversion you have to accept a hit in efficiency, so there is no advantage to sizing a battery bank any larger than what is needed to cover the load long enough to get the genset up and running, stabilized and online. except to limit the amount of starts per day, which rack up costs for starter maintenance/repair/replacement which must be accounted for and compared to battery efficiency, first cost, and depreciation. generally speaking starters are much cheaper than batteries in the long run, unless you need the thing to start every 15 minutes 24/7/365 , in which case larger batteries might be warranted.

on balance if you figure that you need to start perhaps a dozen times a day, a  good starter ought to last 6 months at least, likely closer to a year. in which case i would build my battery bank using not deep cycle but quality starting batteries, and size the bank so that they can carry the load for approx 1 minute while the engine is started and brought up online "while" only taking the top 10% of the batteries total capacity. this places the batteries within the oem  design of normal operation so i would expect approx 3-4 years on a set, perhaps more.  i would also look into the use of AGM batteries because of their ability to take
much higher current charging in the top 10% of capacity relative to flooded lead acid batteries.

i would size the alternator to about 120% of the loads running amps (as measured at the batteries) this way when the engine starts it can run a minute to stabilize
then cover the load, and when the load goes away it can then run perhaps a minute and a half to put back what was taken form the batteries.  this is close for AGM batteries.

small quiet diesel generator? hmm the holy grail!

perhaps a surplus center lombardini air cooled? driving perhaps a 100amp plus leece neville 24volt alternator, or?
maybe one of the yanmar two cylinder water cooled units driving a pair of leece nevilles for 24 or 48 volts?

SOM?  maybe someone can help you with that

your question number 5 i am unclear as to what you are asking,

as for alternatives?  probably as many and as varied as there are other opinions.

fwiw, my opinion, based on all i have researched, tested for, and determined to be true for me.
ymmv of course.

hopefully enough info to help you in some small way, or lead you in a direction that might get you the answers you need.

bob g

[LowGear]

Wow,

I'm flabbergasted.  Thank you all very much for your time. 

I'm smelling money.  I think my $1000 is a pittance for this project.  Darn.

I can't run a small generator continuously for three or four days or should I write I'm not willing to.  One of the nice things about writing on this blog is the thinking that goes along with that writing.

I think the deal breaker here is the inverter.  The batteries are easy.  Four 12 Volt (48 Volts) deep cycle batteries are about $300 at Costco.  A good enough AC battery charger would be what $150?  I see good enough generators go by for about $600 in the Spring and Summer.  But that 4 KW inverter - now that would be some real money.

Casey

[BioHazard]

I think the deal breaker here is the inverter.  The batteries are easy.  Four 12 Volt (48 Volts) deep cycle batteries are about $300 at Costco.

Inverters don't have to be that expensive...
http://cgi.ebay.com/2500-5000W-Stackable-Power-Inverter-48V-DC-120V-AC-/220691297703?pt=LH_DefaultDomain_0&hash=item336239f5a7

I have a 3kw Xantrex inverter that I got on ebay for only about $125 or so. 5kw surge. I haven't been able to do much testing with it yet but it starts a 5000 BTU air conditioner. I believe the manual says that it should start up to a 3/4hp motor without problem.

[LowGear]

BioHazard,

That's interesting.  I'll start watching Ebay and Craigs List.  (You nearly stole the Xantrex.)

Does anyone know of any low cost housing / apartment building Alternative / Sustainable Energy Grants available in Washington State?

Casey

[mike90045]

From my  .sig on the solar board:  http://www.wind-sun.com/ForumVB

Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph )
on a timer for 3 hr noontime run - Runs off PV  via XW6048 inverter

So this is a standard deep well pump, pumping uphill 165' to a storage tank. 

The XW inverters are known to have excellent surge start capacity, when the pump starts,
I never notice it.    3 wire pumps are "supposed" to be a easier start then the 2 wire ones, with the capacitor & relay at the pump, 3 wire's have the cap and relay above ground.

A 1 HP pump = 750 watts while running, correct? 
4200 watt-hr / 750 watts = 5.6 hr until complete discharge. 

When pump is running, inverter claims about 1,000 w even.  The pump has lousy power factor, but if I put the correction cap in, I have to remove the under/over load protection circuit. Tradeoffs.

The XW inverters have a 3 stage battery charger in them, that runs off 240V, which is what the gensets ST head will be putting out, in the winter when I've got no sun.

[LowGear]

Gosh, I can't remember much about the pump.  I put it in around 1972.  I'm pretty sure it was a three wire system as I have a control box up in the garage.  I can tell you that the high power wires that were running over the well at the time aren't much above two sticks of 20 galvanized pipe.  What a rush to look up and see the end just barely missing that hummer.  "One stick at a time Bad-boy" was my mantra for a day or two after that adventure.

And yes I know it's time to start shopping for a new system.  I'm 140 or so feet down and have a pressure tank that is about 2 years old.  Suggestions?  Something that will be gentle with a battery based backup system. 

Casey

[mike90045]

If you don't need a LOT of water at one time, you can wait while the pump, pumps it.  Use a 1/4 hp or 1/3 pump.    Add another 40 gall pressure tank (20 gal of water).  But if you need to water a garden, you will run out of your surge capacity, and eventually only get what you are pumping.

You will have to read the pump catalogs yourself, all the well installers just stuff what's cheap that week, and has a good profit for them, and it's often 2x the pump you really need.

There are 2 specs, the motor, and the actual pump. The catalogs pair a motor with up to a half dozen different pump bodies, and you choose what you need,
1/4 hp : 30' 20gpm, or 180' 2gpm

[elnav]

Lowgear.
FWIW  the wife's uncle  runs a Franklin submerged pump 300 feet down on his off grid homestead.   He upgraded to an Outback 3000 watt inverter hooked to a 48V battery bank consisting of eight L-16 batteries.   It still will not  start the well pump and the uncle can't see  the point  to installing a soft start module from Franklin. We measured  a 7500 watt start surge when driving the pump from a 10kw diesel  generator.
He faces two problems.  Most deep well pumps are  230V  and  most domestic inverters are 120V. Outback's solution is to buy another  inverter wire them back to back to get 230V.  As is he has to start the diesel to run  the deep well pump to fill the cistern where a low power pump them gives him pressure at the tap.
Second problem is the fact  domestically made inverters like Outback and Magnum  use an iron laminated transformer. They cannot deliver more surge than 2X
High frequency switch mode  inverters like the Xantrex Prosine series will deliver  3x surge power provided you use BIG power cables.

In my own designs I use a 230V output  inverter of the switch mode type to drive all big surge motor loads. For 120V utility power I can generally get away with a 4kW step down transformer to feed utility outlets. Most homes use less than 2kW for lights etc exclusiive  of air conditioning and electric heat and of course deep submwerged well pumps.

If you are wondering  where I observed all this. I did at one time work at Xatrex as a marine applications  engineer.
Elnav

[LowGear]

Aloha elnav,

Thanks for your input.  I'll be back on The Dark Side, our nickname for the Puget Sound area of Washington State, USA.  I'll  be looking into some backup - emergency power solutions and may end up with a solar installation.  It all depends on if I can find a grant program.  The main problem is that this is primarily a rental situation and the 30% federal tax credit doesn't apply to them as I understand it.  Without heat or water it can get just a touch miserable.  That happens a few days every winter.  It might be cheaper to just send everyone to a motel for the duration.

I've got to believe that there are better solutions than a 7500 watt surge for a submersed pump start-up.  I'm pretty sure old faithful is a 1/3 hp 3 wire system.  I'll know better next week.

Casey

[wrightkiller]

http://www.epa.gov/greenbuilding/tools/funding.htm

http://your.kingcounty.gov/solidwaste/greenbuilding/incentives.asp

[LowGear]

Hi,

Thanks for the links.  I'll chase some more of these down. 

I'm thinking a trip to City Hall might be a first order of business once I get my muck-lucks on.  It's handy to be able to use some of the key words as I search their minds.

Casey