How can a 48 volt dc generator be used to charge 24 volt battery bank?

solarvic · February 2010

How can I use a 48 volt dc generator to charge a 24 volt battery system? The generator outputs 96 amps at 48 volts and has an ecm that can provide auto startup of generator. Solar vic

niel · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

now you won't get full use of all of the generator's power, but i'm thinking an mppt downconverting controller. what is the ah capacity of the 24v battery bank?
it's either that or a different generator.

solarvic · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

Havn,t got batterys yet but was thinking 4 l-16 batterys. I have a Trace SW 4024 and an exeltech 1100 watt inverter I want to use. This is for a backup system as I have some power outages. Had 3 of them this winter so far. Have a gas well so want to use it some to run the generator. I think this way I could make nearly 100% of the power used. Vic

BB. · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

Depending on the Genset's control circuitry, you might be able to rework it to output 24 volts at 96 amps---Or possibly have it re-wound (probably not worth the effort).

By the way, is the generated designed to charge batteries? If not, that could create its won fun and games.

-Bill

niel · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

bill,
that's why i cited using an mppt controller as it could take a variety on the input voltage. if there's any ac ripple on the generator's output this may need filtering, but i think it could be doable. there's a few good 60a mppts out there. with the use of multiple controllers that generator could put in excess of 175a into the 24v bank. one would be more than sufficient at 60a and percent wise is a bit too much to what degree is depending on which l16 it is.

BB. · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

Niel,

I am a little leary of recommending an MPPT Solar Charge controller used to down convert the output of a generic DC generator (we do not know anything about the design of the genset voltage/current regulator and if it can run with or without a battery bank).

MPPT type controller would be a constant power load on the genset (P=I*V)--and without a "voltage" mode power buffer (aka Lead Acid Battery Bank)--I am not sure that you would have a stable generator output. I worry that the genset output voltage could surge up and down as the controllers attempt to maximize power. Also, different MPPT controllers have different algorithms--So somebody may just end up having to test the combination and see how it works (or not).

However, in this case, the Genset is >>> than controller power... The voltage may be pretty stable regardless of the hunting of the current under control of the MPPT circuitry/electronics.... Just don't know.

-Bill

niel · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

if one cannot use the mppt controller (not sure why it wouldn't work) then that would leave my other alternative in getting another generator. i believe he said it was a natural gas generator and the specs on his or others for his application i am not familiar with. the op may need to fill in some blanks here.

dwh · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

Get a 48v inverter to change the 48v to 120vac then get a 24v Iota charger that runs on the 120vac.

One added benefit is that you will/might have a bit of extra 120v capacity, which you can use while the gen is running to save on battery use. Another is that if your battery/24v inverter system craps out, you can still make 120v by running the gen.

RCinFLA · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

If the generator can produce a little higher voltage to charge a 48v battery system you might be better off buying a 48 v inverter and battery system.

Any 48vdc 4500 watt conversion is probably going to cost more then the generator is worth. Maybe sell it on eBay and use the money to buy an AC generator that will feed the SW4024.

niel · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

dwh,
if as bill says the voltage and general quality of the power outputted from the generator may not be up to snuff for today's top notch mppt controllers then i doubt an inverter would ever work connected directly to the generator. inverters also would most likely require a battery bank to be present as it is not customary to go from a bad or unstable power source straight to an inverter as batteries tend to smooth things out much like a regulator. i don't think he'd elect to have 2 battery banks to do this.
i still believe the mppt controller to be good to use if filtering is observed for any ripple that may be present and of course fusing.

RCinFLA · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

niel wrote: »

i still believe the mppt controller to be good to use if filtering is observed for any ripple that may be present and of course fusing.

Filtering 48v @ 96 amps is not trivial or inexpensive.

niel · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

RCinFLA wrote: »

Filtering 48v @ 96 amps is not trivial or inexpensive.

granted, but he won't need all of those amps and that lessens the requirements. 60a out at 24v is roughly 30a in at 48v. about 1/3 of the genny amps. don't forget that it is a 48v dc generator and i am assuming some effort was made for some ripple rejection.

blackswan555 · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

Depending on the alternator (or dynamo?, please post details) design and configuration you may be able to regulate it down to 24v > 31v, There are smart voltage reg`s available for the marine world that give all the different charge stages programmable, but they are not cheap :roll:
Have a good one,
Tim

solarvic · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

Here is generator description. Brand Is Alphagen for cable systems. I have 2 of them. It has a 5.0 kw rating @ 96 amp and is already set up to charge a 48 volt battery system Has its own built in controler that can be set for whatever type of battery you want to use. It has an ECM that will auto start itself when battery voltage drops to whatever voltage you set it at. Generator part of the system is built by Koehler. I already got grid connected with fronius inverters. wanted to use this system as a backup for power outages. Also figured I would dedicate 3 power uses to this system and let my gridtied system run the reat of the house. Was thinking of running 220 volt well pump, gas furnace and refrigerator on the battery system. I do have a Trace SW 5548 I could use instead of the 24 volt inverters if I have too. I was thinking of converting the 48 volt from generator to keep a 24 volt battery system charged. I have free natural gas to run the generator with. Also have some charge controlers I could use. Going to retire in a couple months and didn,t want to go to the expense of a 48 volt battery system and was trying to use some of the items I already have. I do have a couple of the 60 amp outback charge controlers I was going to try. Vic

RCinFLA · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

Wow, these are first class generators. Noise spec is <250mVp-p from 20 to 100mHz. 60 dbA audible noise from generator.

Appears to be permanent magnet alternator using engine speed control for regulation. To get that low a ripple there must be multi-phase alternator that feeds rectifiers to converter to a near constant D.C. output. It also has RF interference filters on output.

Output spec is 52V @ 96A max. for charging 48 vdc batteries.

I'd go with a 48v battery system and directly charge the batteries from gen.

If you set SW5548 float at slightly below the 52v then it will take the gen output and make AC output. Any excess gen capability will charge the batteries.

( I would love to have one of these for my 48v system to avoid the efficiency loss running through my SW inverters charging from AC generator. Make me a deal on one of them and I will build you a 52vdc to 24 vdc @ 35 amp battery charger)

GreenerPower · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

solarvic wrote: »

I do have a couple of the 60 amp outback charge controlers I was going to try

This might work, follow the OB instructions to set them up for wind/hydro.
GP

solarvic · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

Yes my generator is 3 phase ac with a rectifier to 48 volt dc. One of the reasons I wanted to have 48 volt is I might put up a small wind turbine that is 24 volt. The other reason is I didn,t want to have to buy the extra batterys need for 48 volt. I thought I would post my question here and see what ideas that everyone has. Does anyone know if 2 or 3 charge controlers would charge from the generator output? Since I have a high quality generator it seems prudent to use it. If I can,t get the 48 volt down to 24 I will probably unmount the sw 4024 and go to the sw 5548 I have and try to sell my 24 volt stuff. Vic

mike95490 · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

I would think any of the MPPT controllers would downconvert for battery charging. This was discussed a month or so ago too I think, maybe check the archives?

PWM controllers should not be used, as they pulse the input to the outputs, and only a FET is between the 48V battery and the 24V battery. Ouch !

solarvic · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

I am preety sure 1 controler could be used. What I was needing to know is if 3 60 amp output controlers could be used to make use of all my 48 volt at 96 amp. I already have 2 outback controlers and would only need to get one more. Vic

mike95490 · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

solarvic wrote: »

I am preety sure 1 controler could be used. What I was needing to know is if 3 60 amp output controlers could be used to make use of all my 48 volt at 96 amp. I already have 2 outback controlers and would only need to get one more. Vic

likely, yes. One will always drop bulk first, followed shortly by the other 2. Maybe a Mate or something will get them to all switch at once, but each will have their own setpoints, and they will never all agree, 1 first, and 1 last. But they should get the battery boosted up pretty quick.

What's your thought, one charger per each leg of alternator ? 2, 60A controllers would do it, @ 120A.

Now, when you split the 3 phases out to individual controllers, you get really lousy DC, it's all lumpy, and the ripple may confuse the charge controller. When 3 phases are rectified together, it makes a pretty clean DC, and 2 controllers should share that fine.

Mike

niel · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

each controller may need its own phase of the generator to work from as we can't share all pvs with multiple controllers to go to the shared batteries. i think 60a from 1 cc will suffice in any case.

GreenerPower · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

solarvic wrote: »

I am preety sure 1 controler could be used. What I was needing to know is if 3 60 amp output controlers could be used to make use of all my 48 volt at 96 amp. I already have 2 outback controlers and would only need to get one more. Vic

Haven't done this but I'm pretty sure in your case you can hook 3 OB CCs in parallel. When they are set up for wind/hydro, the MPPT is basically disabled. 60A @ 24V translates to 30A @ 48V on the input. 3 should be fine with 96A generator. You might want to consider a MATE/hub to share the BTS. The MATE would share the BTS info from the CC plugged into port 1 with other devices on other ports. Calibrate all the CCs with a good voltmeter, you should be fine.
You'd need to play with the "park %", the max can be set is 85% (recalled from my memory) that means the CC would try to load the gen voltage down to 85% of the open circuit voltage. This would affect how much current it can draw from the generator, whether you can tweak the park% to get the max 30A drawn (and whether when the 2nd, 3rd CC tries to open circuit to measure the gen voltage while other CCs are loading the gen would affect its internal logic. I think it just tries to load at max to bring the voltage down to the set park %). Try with your existing 2 before buying anymore HW. Crewzer might know more and give you more insight.
GP

RCinFLA · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

solarvic wrote: »

Yes my generator is 3 phase ac with a rectifier to 48 volt dc. One of the reasons I wanted to have 48 volt is I might put up a small wind turbine that is 24 volt. The other reason is I didn,t want to have to buy the extra batterys need for 48 volt. I thought I would post my question here and see what ideas that everyone has. Does anyone know if 2 or 3 charge controlers would charge from the generator output? Since I have a high quality generator it seems prudent to use it. If I can,t get the 48 volt down to 24 I will probably unmount the sw 4024 and go to the sw 5548 I have and try to sell my 24 volt stuff. Vic

There was a thread within last couple of weeks of someone looking for an SW4024 to replace one used in a series stack 240vac setup.

RCinFLA · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

niel wrote: »

each controller may need its own phase of the generator to work from as we can't share all pvs with multiple controllers to go to the shared batteries. i think 60a from 1 cc will suffice in any case.

You need the three phase, full wave rectified output to keep the ripple down. This is same as automobile alternator.

For a three phase full wave rectified D.C. with r.m.s. of 52 vdc, the pk-pk ripple is 7.3 volts. Min. is 47.13vdc, Max. is 54.42 vdc. It does have some filtering but appears to be primarily for higher frequency EMI reduction.

A filter cap for a single phase at such high current is almost impractical. It would also not be wise to include an internal electrolytic cap within the heat confines of a generator.

If all you are considering is a 370-420 A-Hr L16 battery string then a single 80 amp charge controller should be sufficient.

If a filter cap is used, it would be much easier on a three phase output. If you want to reduce ripple to 0.5 v pk-pk, at 96 amps, with min rpm of 2800 rpm, will require a 25,000 uF cap. At lower current ripple will be approximately linearly less. This is very do-able. Would recommend using a 75vdc rated cap, at the remote power junction to avoid generator heat. The rms vdc will be slightly higher, closer to 54.3 vdc which is not all that bad for charging close to desired float voltage.
http://www.surplussales.com/Capacitors/Electrolytics/10000uF-300000uF.html

niel · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

granted about the ripple being worse, but you missed the point about the bolded words. for the batteries he has in mind the 60a from 1 controller may in fact be a bit too much current and more than 1 controller would fry the batteries he has in mind. this makes 2 or 3 mx60s being used on the generator a moot point unless he plans to expand the battery bank's ah capacity.
to quote the op,
"Havn,t got batterys yet but was thinking 4 l-16 batterys."
now trojans don't like over 13% so 60a/.13=461.5ah capacity. l16s are either 325ah or 370ah depending on which model he chooses. these are 18.46% and 16.22% charge rates respectively at 60a in. he could double the battery capacity by going with 2 strings of 4 l16 batteries and still be well within a good charge area with 1 mx60.

GreenerPower · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

niel wrote: »

... for the batteries he has in mind the 60a from 1 controller may in fact be a bit too much current ...

Good point. He can dial the charging current of one CC down to match his battery for now. Turn on more CCs if his AC load increases to reduce current drawn from battery. His 2 existing CCs may be sufficient for his current inverter wattage unless he'll expand in the future.
GP

solarvic · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

I thoght I needed to use all the 96 amp of the 48 volt gen set to be eficient. So if I don,t make the gen set work hard making all the 96 amps is it good for the generator. Does it burn less fuel also? The gas is free but I don,t want to waste it either. I probably won,t be using the generator much anyway as I probably might connect 3 or 4 solar panels too. Right now I am grid tied with 14 kc-158g panels on 1 inverter and 12 sharp 167 ndu-3 panels and 2 mitsubushi mf-175 ud5 panels on other inverter. Since I have some power outages I want to use the offgrid system as a back up and might dedicate my fridge and water system to the off grid inverter system. Solarvic

BB. · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

In general, a fixed RPM consumer sized genset's fuel use pretty much flattens out at 50% capacity (just my observation whenever I could find specifications for various gensets on the web)...

The Honda euX000i family (and some of the other Yamaha and such) use Inverter/Alternator's that allow the engine RPM to be cut way back when operated at low power levels... The eu2000i maintains a relatively fuel efficient kWhrs/Gallon down to 25% or less (4 hours at 1,600 watts and 1.1 gallon of fuel--to 15 hours at 400 watts and 1.1 gallons of fuel).

Your DC genset seems to be, somewhat, variable in RPM ( 2800 to 3600RPM)--if they drop the RPM at low output currents--it should stay pretty energy efficient at less than 50% rated electrical loading.

Since they give you the flow rates of 80ft3/hr for natural gas--I would fire the genset up and run it with no load--and see how much fuel (natural gas or propane) it consumes. Figure:

say unloaded generator runs at 30 cuft/hour (run for 10-15 minutes to get usable reading)
5,000 watts * 30 cuft per hr /80 cuft per hr = 1,875 watts is probably minimum fuel flow

Given that it is probably a bit less fuel efficient at full loads, the actual minimum fuel flow is probably 10% or so less efficient--or closer to 1,700 watts at minimum fuel flow.

The assumption would be that below ~1,700 watts (in my made up example of 30 cf/h) fuel flow would remain relatively constant at 30 cf/h from 1,700 watts to 0 watts load.

Not 100% accurate--but good enough for planning a near optimum setup (minimum efficient load sizing on genset).

-Bill

solarvic · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

[EMAIL="http://www.provantage.com/tripp-lite-aps2448ul~7TRPI01F.htm"]http://www.provantage.com/tripp-lite-aps2448ul~7TRPI01F.htm[/EMAIL]
I was wondering if this wou;d work to connect to the 48 vdc generator so I could have a backup when there is a power outage? S:Dlarvic

niel · February 2010

Re: How can a 48 volt dc generator be used to charge 24 volt battery bank?

that depends on some factors like how well regulated your 48vdc output is as it could go too high or too low to function properly with the ups. odds are the voltage will be ok seeing the range on the ups. also if there is too much ac ripple it can be a problem. i don't believe this is a sine wave inverter, but it is hard to say as they fail to specify modsine or sine or even the thd % as they decided to use a generic term of "Pulse-width Modulated Sine Wave". anybody put these on a scope to determine if within spec for sine wave? to me it says modsine and won't be suitable for any motors, fans, or compressors. i wouldn't count on being able to run its so called wattage rating on a continuous basis either. other than this stuff you can use it for lights, tvs, etc. during an outage with it automatically kicking on. will your generator automatically kick on? if not then you better have a sizable battery bank to run it.

How can a 48 volt dc generator be used to charge 24 volt battery bank?

Comments

Categories