15000 watt generator and 27 6 volt batteries

System · March 2011

I have a 15000 watt generator that I want to charge 27 6 volt batteries. I have a bridge rectifier for the generator and it converts the single phase AC to 240 volts DC at I am calculating at 92 Amps unloaded. As far as how much it will supply under load Im not sure.

I would imagine I would need a combiner box to get the voltage down to a point the charge controllers for the batteries (I want to use several charge controllers)

Ive been seaching the web, am I thinking correctly that this can even be done?

Cariboocoot · March 2011

Re: 15000 watt generator and 27 6 volt batteries

I don't want to sound nasty but ... you are so far off the mark with your reasoning that you should not attempt this. It will be bad.

First off you have a 15 kW generator which will put out a lot of power. About 63 Amps @ 240 VAC. That alone is enough to kill you.

Second, twenty-seven 6 Volt batteries does not add up to any viable configuration in either series or parallel. All in series would be about 172 Volts DC, with enough current behind it to weld steel solidly. Or kill you.

Third, merely adding a rectifier to an AC supply doesn't make a battery charger. It just makes unregulated DC. In this case at enough Voltage and current to kill you.

To properly charge batteries you need a battery charger that regulates Voltage and current so you're not just feeding the batteries random amounts of power. Batteries that are supplied with too much can heat up, gas off, explode, and kill you.

Do you see the repeating theme here? I don't mean to be alarmist or insulting but what you're proposing is quite dangerous.

Better you should buy a bunch of cheap automotive-type chargers with a 6 Volt setting and have the generator run them simultaneously. If these are deep cycle batteries, they will want a charger capable of both a bulk and absorb charge stage.

Please read the battery FAQ's: http://www.windsun.com/Batteries/Battery_FAQ.htm

KeithWHare · March 2011

Re: 15000 watt generator and 27 6 volt batteries

michaeljayclark wrote: »

...
now, the warning aside, how can this be accomplished?

Seems like Cariboocoot answered this question:

Cariboocoot wrote: »

...you should buy a bunch of cheap automotive-type chargers with a 6 Volt setting and have the generator run them simultaneously. If these are deep cycle batteries, they will want a charger capable of both a bulk and absorb charge stage.

Is there a good reason to build something yourself when there are relatively inexpensive commercial off-the-shelf devices that are designed and tested to do what you want to accomplish?

Keith

hillbilly · March 2011

Re: 15000 watt generator and 27 6 volt batteries

Maybe a few more details as to what exactly it is you're trying to do. The little info you give does indeed sound not only dangerous but sounds like you don't understand the basics. Perhaps that's not correct, but given what you asked I'd say 'Coot had some reasonable advice. Without a clearer picture of the whole set up I wouldn't even begin to know where to start as far as advice other than "don't do it".

Photowhit · March 2011

Re: 15000 watt generator and 27 6 volt batteries

27 is an odd number, and you should check the battery FAQ's. First problem I see is that likely these batteries are salvage and hence have different ages, and prior lifes. Batteries age together and sould be charged together with like age/use/capacity batteries. If you don't know this, best to charge one at a time!

I don't know of any charge controllers that could handle this, other than drawing what they need back through an inverter with charging capacity, so this question might be better put to the Advanced section rather than off grid.

Other than that, see Cariboocoot's answer, sorry.

icarus · March 2011

Re: 15000 watt generator and 27 6 volt batteries

pretty much anything can kill anyone.

anyone like to answer this question and not just say dont do it, it can kill you?

I thought forums were to discuss situations and offer solutions.

Dont worry, I here what you are saying and have taken it to heart. I am stringing 60 3000 farad ultracapacitors at 2.7 volts each, now thats alot of power!

now, the warning aside, how can this be accomplished?

Might I suggest a couple of things. First, yes, these forums are indeed here to discuss situations an offer solutions. Please don't take those offered (and those offering) solutions the wrong way. 'Coot's response was perfectly reasonable given the amount of information you gave us. That said, this forum is populated by some very smart folks, many who are EE's, Solar Designers, installers, etc. Many have "forgotten" more about batteries, generators, solar systems etc. than most of us will know. They bring to the table years, indeed decades of solving all sorts of esoteric problems, so don't get snotty and dismiss the answers out of hand. The bottom line is that many here have been there, done than, and the great advantage of this board is that you don't have to reinvent the wheel each time.

So, as to your problem, please explain in a bit more detail what it is you are trying to achieve, what your configuration is likely to be etc. Just for the record, 15 kw sounds to me to be a lot of potential power for 27 batteries. Depending on the AH size. I personally charge 4 T-105's with an Eu 1000 running at idle. (20 amps/12vdc into 450 ah of batteries.)

Welcome to the forum and good luck,

Tony

System2 · March 2011

Re: 15000 watt generator and 27 6 volt batteries

This has to do with an electric vehicle. The setup is to have the vehicle range extended by a generator. Id like to have the setup able to be charged through the generator and through the grid.

Ive priced 30 amp 6 volt chargers at $50 each, 27 x $50 = $1350

the reason for 30 amp is in EV's the higher amperage is the best bet.

There are very few "smart" chargers that can deliver 30 amps unless you go with manzanita micro at $3000

27 batteries to be 160 volts.

the reason I ask is on this forum under off grid is I an essentially charging a group of batteries off grid just like a solar system. I asked about using charge controllers instead of battery chargers for that purpose. 30 amp charge controller can be found for less than $50. not great ones anyway but still.

dc to dc converters at 30 amps are $200 each.

This is just looking at off the shelf components.

in a large string of batteries individually charging them is the best way to go. otherwise when they get older they all age the same and then if one goes bad the whole pack needs replaced.

these are the things I am looking at

niel · March 2011

Re: 15000 watt generator and 27 6 volt batteries

fyi, charge controllers would only be a portion of the equation in configuring a utility type charger and only a few of the more costly ones have an input voltage capability higher than 150v. the input to the cc would need to be filtered dc with low ripple and preferably through a transformer just for safety's sake. unless you really know what you're doing i would advise against doing it this way.

john p · March 2011

Re: 15000 watt generator and 27 6 volt batteries

May I ask where does this fit in to the scheme of things ??? and how are they being charged??? I am stringing 60 3000 farad ultracapacitors at 2.7 volts each, now thats alot of power

System2 · March 2011

Re: 15000 watt generator and 27 6 volt batteries

the ultra capacitors will be in parallel with the battery pack. The idea is to have the capacitors handle any high demand for power above 250 amps, deliver the current, then the batteries take over and will only see a demand less than 250 amps. the batteries then will equalize with the ucaps as they drain.

there are evs that use capacitors and they are seeing that effect. The caps those EVs are using are regular capacitors and not ultracapacitors.

shunts on the battery bank and ucap bank will tell me what amperage is going where.

as far as a tie in to this thread, I think a bank of ultacapacitors in an off grid system could level out demands for power. in fact, DEKA is working on a hybrid battery with ultracapacitor plates with the lead acid battery. They will demonstrate the capability of these battery by using them in the power substation at the east penn battery plant in pennsylvania to handle high load demand and level out the power.

those batteries would work nice in an off grid system.

icarus · March 2011

Re: 15000 watt generator and 27 6 volt batteries

So, by my calcs, 160 volts X 30 amps (which seems to be your target) equals ~ 4800 watts. I would than ask the question, why the 15 kw generator?

What about wiring the batteries with a number of AB switches so that you can charge 8 batteries @ 48 vdc? That would leave 3 batteries left over that could be charge at 12/6 vdc? 3 48 vdc battery banks, plus one 18 vdc bank. Just an idea.

Tony

BB. · March 2011

Re: 15000 watt generator and 27 6 volt batteries

A question on the capacitor bank... Are you planning on placing the capacitors in parallel with the high voltage DC battery bus or is each behind some sort of power converter that allows each energy storage bank to operate on its own I/V curves?

The issue is that batteries, for the most part, are Voltage Sources and operate on a fairly flat voltage curve (chemical energy sets the voltage level). Whereas capacitors operate on a 0.5*CV^2 curve where the energy level is represented by the differences in the square of the voltages.

Also, at least up to this point, I am not sure that ultra capacitors have a huge advantage over batteries because of their limited cycle life if you start really exercising the caps. Ultra Caps are still much larger than equivalent sized batteries for energy storage and have a lot of implications in the wire management/dc converter design because of the wide operating voltage range.

A few years ago, I had read an article about (I think it was) a subway/train design that used ultra caps instead of batteries for their transitional power supply and they were having to replace the caps after ~1 year because of wear out.

-Bill

john p · March 2011

Re: 15000 watt generator and 27 6 volt batteries

Ultra caps lifespan
At work we have our favourite "toy" a 100,000farad 24 v bank of ultracapacitors.
This bank has now been charged /discharged about 3 hundred times and while we have not accurately measured its capacity loss we estimate it is now down 20%.
I dont believe there is any possible way you could connect a string of 60x3000 caps in parallel with batteries to recharge them
Fully discharged they present an incredible load on the charger. I cant off the top of my head give you and exact figure but no battery charger could recharge them they appear as the closest thing to a short circuit.
We have 4 very heavy duty chargers to recharge them.
They are also incredibly dangerous things to play with,you can easily blow various body parts of of you if you come into contact with an even "apparent" discharged bank
I give example of the destructive power.. ours are mounted on a very large trolly remote controled(you could not fit them into a road going motor car) at the end of the trolly there is a length of solid copper 1inch dia if it is brought to within an inch of a metal object that the bank of caps is also connected to like a v8 engine block it will remove pieces of the block and in the process loose about 4inches of the copper rod.. NOW what you think that would do to you???

Cariboocoot · March 2011

Re: 15000 watt generator and 27 6 volt batteries

Hint: the answer was given, repeatedly, in post #2. :roll:

techntrek · March 2011

Re: 15000 watt generator and 27 6 volt batteries

icarus wrote: »

So, by my calcs, 160 volts X 30 amps (which seems to be your target) equals ~ 4800 watts. I would than ask the question, why the 15 kw generator?

Add in low power factor on the charger(s) and it might only be slightly oversized.

oil pan 4 · March 2011

Re: 15000 watt generator and 27 6 volt batteries

If all the batteries are in the same condition and you want to hook them up for 48v or lower you should be able to get a used industrial charger fairly cheap no problem. If you need them wired up in some higher than 48 volt configuration. The easiest, cheapest, most dangerous way I can think of to charge them is to get a 240v 5kw variable AC transformer that puts out 0-300VAC (like I have). Put your bridge rectifier on the out put and attach an amp meter and volt meter so you know whats going into the batteries, put a fuse in line and have at it.
Charge voltage should be about 2.4v per cell.
So If you want to serries up all 81 cells, you are looking at a total max charging voltage of about about 194vdc. Also limit the charge current to about 10 amps per string of batteries.
The danger level on this build would be a little high even for me and well beyond extreme for any one who didnt do work on power generation and distribution systems as a normal day to day thing.

15000 watt generator and 27 6 volt batteries

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