I seem to have built myself into a corner. 24v bank/12v inverter

System

Hey Everyone,

My name is Jason and I am new to this sort of thing but have a lot of
applicable knowledge. I have put together a 24v battery bank @ 400
Ah but only have a 12 volt inverter. They are 12v batteries at 100 Ah
each so tapping into half the circuit creates a major problem. I want to
keep it simple.

So my question is should I just invest in a 24v inverter? Or are there
any good DC to DC lossless (stepdown) converters that would work
without all the the diodes and extra cables. My budget for this project
is very limited so I must do my best to keep it simple.

Looking at about 32ft for DC current. Should I just use a 12v bank?

Thanks for reading,

Jason

BB.

Re: I seem to have built myself into a corner. 24v bank/12v inverter

There are converters... But they are not usually very big...

Samlex 24 Volt to 12 Volt DC to DC Converter, 15 Amp
12/24 Volt DC/DC 20 Amp DC-DC Converter

If you have to send your current very far (32'x2=64' of wire)--12 volts is about the worst voltage to do this with... Unless your power requirements are very low, or you have some very heavy gauge cable to send it across.

Picking a higher DC voltage does make sending power across a distance easier--But, using an inverter and sending the power 32' is probably the best thing to do...

Can you elaborate about what you want to do (how much power, how far, what is the end need--12 vdc/120 vac or what).

-Bill

System2

Re: I seem to have built myself into a corner. 24v bank/12v inverter

HI Bill,

Thanks for such a quick responce. Looking to reduce my grid consumtion of about
2000w daily. Yeah the higher gauge DC cables would not be worth the cost. And
AC over the 32ft means 560lbs of batteries in the attic. Hmmmmm thats not a bad idea,
although service would be trouble. Thanks for the link, the amperage requirement
would be sufficent but I could get a 24v inverter cheaper. Wife is going to be p*ssed,
"yeah I just need one more componet". (she's heard that before, He He LOL!)

This is a Solar project by the way. I have sources for the batteries since I am a
Electric forklift mechanic. Just trying to work out the bank and load for now.

120V AC Load at 15 DC amps minus losses and I would be a happy camper!

Still need to work out the Solar Requirement and as I learn it will be massive!

But that is how we learn, Thank You for your assistance!

Jason

P.S. Google "Ceramatec Battery" and look at the first and second listing.

If this is true it will change everything! No listing in the stock exchange,

I already looked

icarus

Re: I seem to have built myself into a corner. 24v bank/12v inverter

Get a 24 vdc inverter.

I would avoid putting batteries in the attic for a variety of reasons,, the biggest is they will be subject to significant heat that they don't like,

Tony

BB.

Re: I seem to have built myself into a corner. 24v bank/12v inverter

Jason,

Is your load 2,000 Watts * 24 hours per day (48 kWH per day, quite a bit of power)--or 2,000 Watt*Hours per day (~80 watts * 24 hours per day--pretty small amount of power)...

I am not quite sure if you are looking for more help from us or not (more than happy to help).

Sounds neat that you have a good source of forklift batteries--which can be very nice for a solar RE system.

In the end--we try to talk people into doing as much conservation first, as it is almost always cheaper to conserve a watt*hour than it is to generate it.

A Kill-a-Watt meter is great for the 120 VAC 15 plug-in loads. For larger loads (A/C, 240 VAC, etc.) a whole house unit like a T.E.D. or equivalent (Google is rolling out a project for web tracking of home energy usage) can be useful too.

Take a look at the big picture (what are your loads, what are you looking for--reduction in cost; emergency power; both), etc...

In the end, a few quick rules of thumb... A good starting size for the battery bank is 3 days of "no sun" and 50% maximum discharge or ~6x your daily loads (in Amp*Hours or Watt*Hours).

Another good rule of thumb is plan on your charging to be in the range of 5% to 13% of the battery AH (20 hour) capacity. Below 5% with solar, takes forever to recharge, can't equalize well. Above 13% (depending on battery constructions) and the batteries tend to get hot (and nobody can afford all the solar panels to charge at this rate).

Another is that the end to end efficiency of a solar array + charge controller + battery bank + inverter works out to ~52% of the rated solar panel wattage...

For example, 1,000 watts of solar panel, over "5 hours of sun" per day (Utah can do that for 8 months of the year) and 52% derating will provide 120/240 VAC useful power at the outlet of:

• 1,000 watts * 5 hours sun * 0.52 = 2,600 Watt*Hours per average day

Of course, in summer you will get more. And winter you will get less.

Hope the above helps.

-Bill

niel

Re: I seem to have built myself into a corner. 24v bank/12v inverter

acetechnician,
you've even got me slightly confused here. you state 2000w in a day. does that mean 2000watt hours aka 2kwh? later you say 120vac loads with 15adc. is the 15adc at 24v 12v or what? 15a at 24v is 360w or is that 15ah (ampere hours) for 15ah x 24v = 360wh? if 360wh the over 24hrs this would be 8640wh or 8.64kwh. even if you meant the 15a as ah and at 12v then this is still much higher than the possible 2kwh as it is 4.32kwh.
if your inverter is modsine at 12v then you might want to consider a sine wave inverter at either 24v or 48v.

System2

Re: I seem to have built myself into a corner. 24v bank/12v inverter

Tony,

Yes the heat would be tremendous and not viable for this situation.

Bill,

Of course I am looking for more help, that's why I came here!
Thanks Again!

niel,

Your math is confusing, please forgive me. I seem to be confusing
time Vs power consumption.

I will review,

Thanks again,

Jason

myocardia

Re: I seem to have built myself into a corner. 24v bank/12v inverter

Jason, welcome to the forum. You will be needing both a 24V charge controller (or do you already own one?) and a 24V inverter. As far as charge controllers, I like the Xantrex C-series: http://store.solar-electric.com/xachco.html or the Morningstar TS-45: http://store.solar-electric.com/trts12vochco.html for good performance at good prices. You'll get more power (especially during the winter, when you need it the most) from an MPPT charge controller, but the good ones start @ ~$400, and go up quickly from there.

As far as inverters, do yourself (and any and all electronics, battery chargers [think laptop], and all electrical motors) a huge favor, and spend a bit more for a true sine wave inverter: http://store.solar-electric.com/sasiwain1.html There are actually quite a few products that will flat out refuse to run on a "modified sine wave" (non sine wave) inverter. And even though all motors will, it is very hard on them, not to mention that they use 25%+ more power when given a square wave, instead of a sine wave. The old adage "You get what you pay for" goes double when it comes to inverters.;)

john p

Re: I seem to have built myself into a corner. 24v bank/12v inverter

no such thing as a lossless step down dc to dc converter