Please Help With My Battery Bank Configuration 12 24 48

[throwinstones]

Hello to all,

Haven't been on the board in a while.

Winter is on its way and I have again filled my shop with stirling engines, generators, panels etc...

I've finally flown my first genny last week.

My problem is that I have 48v genny, a 24v battery configuration, and a 12v inverter.

The 48v was chosen to reduce wire costs at 200'

I would appreciate anyone helping with my battery configuration.

I have a 24-volt system composed of 6 battery cases, each case contains 4-12v batteries, these then connect in parallel.  In addition there is a 24v APC UPS, this allows for computer monitoring of loads and battery condition. It also allows for the ups to be a 24v/650watt inverter.

Unfortunately the UPS itself takes up allot of juice when its on because of fans and electronics, I also cannot get it to stop beeping.  I basically use it as an additional battery bank.

I have modified one of the battery cases as pictured below, I have left out the additional cases in parallel for simplicity.

My problem is that when I tested the other day I only got about 30 minutes running 2 40-watt light bulbs from the 12v inverter.

Any comments would be appreciated.

I really don't want to spend any more cash on things like step down and up transformers. I'm already double the budget.

Thanks in advance

[Roamer195]

Too many wierd configurations that will give you uneven charging.

Choose 12v, 24v, or 48v for your bank voltage and put the whole bank together that way.

If you make the bank all 24v, then you can use this kind of bucking converter to step your 48v down to charge the bank. All you need is a good, big inductor, like the low-voltage side of a microwave oven transformer or something similar. Then you need a good power transistor(s) and a fixed frequency pulse circuit to drive it.

http://www.powerdesigners.com/InfoWeb/design_center/articles/DC-DC/converter.shtm

The very first circuit on this page is the one you want. The difference is, just substitute your 24v battery bank in place of the output capacitor in that circuit. Top is positive and bottom is negative terminal.

[chux0r]

Another possibility is to use transformers on your AC coming out of the generator.  If you step down each phase (that's 3 transformers for 3 phase) before rectifying, you don't have to worry about doing AC/DC conversions afterwards.

Of course it would be awesome to rewire your stator if it's such that you can do that.  For example if each phase has 3 coils in series, you could just rewire them in parallel and get 16V at the same RPM as you got 48V with them in series.  (Possibly introducing other issues, but the more experienced folks can help me with that.)

Or if you stator is in star, you could rewire it for delta and get ~28V.

I'll agree with Roamer that if you center-tap your battery banks... and center tap your center-taps, you'll have all kinds of weird issues, unless you have some way of making sure you draw power equally from each cell... which is nearly impossible.

The only thing I can think of is if you completely cycle each battery on a schedule.  Which would be inconvenient and impossible to do if it's not automated... but if you 48V bank starts at 0% DOD, then you go into "load mode" and put your 12V inverter on the first battery until it's down to 20% DOD.  Then move on to the second, third, and fourth.  When all four batteries are down to 20% DOD then you have the option of going back to "charge mode" and hook the whole 48V to the genny, or go back to round-robin discharging each battery.  But you'll really want each battery to be at the same level before you start treating them as one in series.

I'll be watching this thread closely, because I'm incrementally building my setup very cheaply, and I expect to start introducing some mismatched components at some point or another.

My instinct: 12V inverters are a dime a dozen, so you shouldn't have invested too much here.  Sell it, and buy a 24V unit.  Try to get your genny producing 24V (or take the hit in amps and let your batteries pull it down), and configure your battery bank for 24V.  You won't be at 100% efficiency, but it sounds like you (like me!) will be happy if it works at all, and it will.

[nothing to lose]

"My problem is that when I tested the other day I only got about 30 minutes running 2 40-watt light bulbs from the 12v inverter."

Sorry I can't help with the questions, but are you sure your batteries are ok??

 I used to run most the night with a 100 watt bulb or more on just a car battery years ago.

Was some cheapy inverter, about 300watt or little more.

So it sounds pretty low for 30 minutes at 80 watts to me, unless you have really small batteries I guess.

[tecker]

  The problem that I see is any voltage drop in the battery combo that powers the 12 volt inverter pushes the battery to conduct across as well as provide current . Also the battery never really tops off when charging in series . Use a regulating controller

to provide the 24volt charge off the 48 volts from the genset the higher voltage will be seen as current  .Isolate a set of batteries  for 12volts and and charge those also with a regulating controller . That would have you adding two power supplies and your good.

[nothing to lose]

To stop the beeper on my UPS I just broke it off! Then of all things I saw a button on the front to shut it off afterwards

Very waistful, but you can probably run the UPS off the inverter for 120vac input and charge batteries using the UPS then. Mine is 600watts and 24 volts. So if you had the same thing, you run 12vdc to the inverter, 120vac to the UPS, and the UPS charges 24Vdc to the other batteries. You could use the UPS as normal and if the 12v battery bank goes dead and the inverter shuts down you go to backup power off the charged 24v bank and the stuff on the UPS still runs.

Course your gonna get lots of loses that way too, but it should work. I don't know how good the UPS charger is for output, mine keeps the batteriers charged but I don't use them for anything else very often but backup and I am running mine on the grid still. Hopefully I will have several genies flying by the end of next week!

Just bought more batteries, have a load tester waiting to be picked up and waiting on UPS to deliver some more stuff too. If I had gennies up today I could have turned off the grid for awhile!

[richhagen]

I'm not sure I'm reading this right, and I could be wrong on my analysis, but, you've got a 48 volt generator and a UPS that runs off of 24 volts and a 12volt inverter.  If it were me, I'd keep the 48V source at 48 volts.  Arrange the batteries in a 48V bank, save up, sell, or trade for a 48 volt inverter of a size suitable to run the required loads in place of the 24 volt and the 12 volt inverters. If necessary I'd obtain the cheapest isolated chargers (or a 48V model) to charge the batteries from the grid (if thats what your doing to supplement the 24 volt UPS now?) You could probably build a cheap and simple circuit to trip a relay if the battery state of charge was below a certain point that would turn on the grid connected chargers.  Or for that matter since it would only function in the bulk stage anyway, you could build a charging circuit from a suitable transformer, bridge rectifier and a few other components.  Anyway, I think if you end up with a system that is all at the same voltage, you will have greater long term stability in terms of battery life and ease of management.  In that regard, it is my opinion that 48V is the best of the three voltages to use because for any given power, the wiring, breakers and other hardware components are usually smaller and cheaper.

It seems to me that your current system would be bad for the two end batteries on the 48 volt string with no loads on them as they would likely be always overcharging and electolysing there electrolyte.  Same problem with the one in series with the battery powering the 12 volt inverter.  As you draw down the voltage using the inverter, the 24 volt strings from the UPS will send current back through that string to equalize the voltage when nothing is being drawn on the one in series with the battery the UPS is attached to.  

In the mean time I'd probably hook the 12V inverter to one of the batteries on the 48V string which do not currently have a load on them, or better, through a dpdt switch, if available in the appropriate amp range, to select either of the two batteries with no load on them now.  To periodically check the states of charge, just use a meter.  

Take this for what it's worth, I don't claim to be an expert, just trying to help.  Rich Hagen.

[Nando]

First : you are going to damage the two upper 12 v batteries that you are using to compensate for the 48 volts generator.

Bad idea for the 12 volts inverter -- bad connection -- drop it

Keep everything 24 volts and regulate or drop half power until you arrange a better system

What is the peak current of the generator ?.

I did one arrangement like yours, where the batteries were set 48 volts and the DC/AC converter was 24 volts.

Then I had a DPDT relay that switched the converter from one 24 volts bank to the other, the circuit triggering the relay was reading always the loaded bank section, also if the non-loaded 24 V bank was fully charged then the relay was as well triggered.

You loose power for about 20 milliseconds during switching, until I placed a small battery always on the Converter side to give power during the switching, the arrangement lasted for a year, time that took me to place a 48 to 24 volts converter to charge the bank as a 24 bank from a 24 Volts source.

About 30 to 60 dollars

Some UPS do have a LOUSY efficiency around 60 to 70 % instead of the desired 90 %

Regards

Nando

[Roamer195]

I would actually like to see a big relay board to "shuffle" the batteries around. Not very practical. But, it would be a pretty cool "puzzle" project.

[DanB]

I wonder what sort of wind turbine you have? and how large the prop is?

200' is not unreasonable for a small 12 volt machine, there will be some losses, but probably not too bad under normal wind conditions and the wire should not be too aweful bad.

You need to run your whole system at the same voltage to do things right here...  There are certainly advantages to 48 volts, but you really should spend the $$.. and get a 48 volt inverter.  The cost of ruining your batteries (or not getting the most of them because your tapping part of the bank) may outweigh either the cost of a stiff line for a 12 volt wind turbine, or the cost of a new inverter.

As you have it setup... your losing more power from your wind turbine in the weird battery arrangement than you would if you just had a 12 volt wind turbine with some line loss I think.

If your wind turbine is say... a 6' machine, then in 'average' say... 10mph winds, you might be getting 3-4 amps at best?  In average winds, your losses over #10 romex would not be bad. Then again.. I don't know how big the machine you have is.

[throwinstones]

Thanks for all the info.

The Genny is an Air 403 48v.

Running 10awg wire

I Beleive that I am going to disassemble the Battery Packs and UPSs and rewire into a 48 volt config.

I guess I will then either get a 48v inverter or 48-12 v dc-dc step down transformer.

If anyone has this stuff and wants to sell or trade for my 1200watt 12v inverter please let me know.

Thanks Again.

[ghurd]

We used some DC-DC converters from Powerstream.

They were much less expensive than most, important for an experiment.

They work well. The numbers they give were about what we tested.

Been running about 2 and a half years, maybe 3 hours per week.

They had quite a large selection. Even some strange ones.

G-

[throwinstones]

Hi Found sevral dead batteries in the bak so far.

Heres the drawing, At one point I had the inverterin a different spot as illistrated.

Thanks