Ideas For 675 Ah 48 volt Battery Bank Charger?

Hi.

I have a 48 volt battery bank (675 Ah) supplying my Outback Inverters which are connected to my house wiring. I am looking for a way to charge the batteries until I get the cash to get some solar panels. Right now I am using one inverter to supply AC and another one only to charge batteries. The problem is that it will only charge at up to about 20 amps.

Are there plans somewhere that would show me how to build a regulated battery charger in the 100 amp range? If not a battery charger then perhaps a power supply? It would need to be able to go up to about 62 volts. So far I've only built little 12 volt, 1 1/2 supplies. If I can't get 100 amps can I get 50?

Would it be possible just to use a step-down transformer from 120 VAC to about 60 VAC or so and rectify it? Would one 12,000 uF capacitor be enough to smooth out the AC ripple? I've read that deep cycle wet cells do not like ripple.

Another possibility might be a DC generator and the voltage could be adjusted by engine speed. If I was to acquire a permanent magnet DC motor is there a simple way to determine how many amps it would put out at what voltage at what RPM? I've looked at many online and something in the 1725 RPM range seems like it would be easier on a small engine (and quieter if the engine is running at half speed) but so far I've not seen any motors rated at more than about 30 amps.

If all else fails I'd consider building a permanent magnet alternator from scratch. I've read about building PMAs for wind generators and it sounds like to get more current I would need to wind the coils with larger diameter wire and fewer turns to reduce resistance. All of the plans I've seen call for six coils but I'm thinking 9 might work better for higher current. Most of them also call for two rotors containing 12 magets each but I'm thinking that is just so there is more output at low wind speeds and if I'm using an engine then 1800 rpm or higher is not a problem so I was thinking six magnets might work. Anyone know it it can be built with 9 (or more) coils and fewer magnets?

Any other ideas?

Thanks.

Reply to
Ulysses
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I'd start out trying to use a BIG variac with a BIG bridge rectifier and a couple BIG caps. Manually adjust the voltage. Might need a 50A shunt. Big DC amp meters are pricy. You can get all this stuff at Skycraft Parts and Surplus in Winter Park Florida (skycraftsurplus.com)

Reply to
BobG

Inverters which

the

I am

batteries.

perhaps

volts. So

100 amps

You want plans for a 6KW charger ?

VAC to

AFAIK no capacitor is needed.

that's news to me.

A big inductor might work better.

motor

what

ask the maker? measure it?

Bye. Jasen

Reply to
Jasen

Um. I don't know what I was thinking when I wrote that. I guess I wasn't. Let's make that 60 amps which would almost be the C10 charge rate and could run from a 5000 watt generator.

I've also read that they do, but that was a long time ago.

I've been looking at surplus stuff and usually the current draw, running speed, and voltage are indicated but I don't know if that transforms into the same thing if driven by an engine and used as a DC generator.

Reply to
Ulysses

I like that idea. Thanks.

Reply to
Ulysses

60A into 55V is 3300W, that should work.

if you don't need isolation go with the variac plan.

not even close. that'd reduce the ripple amplitude by about 1V (based on guessed parameters)

I guess it's possible ( but capacitors are bad. they reduce the power factor of the load, meaning you'd need a stronger 120V supply, variac, and possibly a bigger rectifier

the inductor works to smooth the charging current this will knock the peaks off reducing ripple to the battery and improving the power factor to the source.

a large 24V (automotive) altenator run at 7200rpm should be able to produce the current and voltage you want. you'd need to replace the

24V regulator with one designed for 48V batteries, possibly you'd need to replace the rectifier too.

if it's a used, one while you're at it fit new brushes and bearings etc. dead brushes are a hassle but a bearing failure is a disaster.

the automotive altenators have two advantages over a single phase

120Vac supply

the voltage is independant of the motor speed and easy to control, the output frequency is higher so the ripple is easier to filter out, and they're three phase so there's much less ripple to start with.

not all that suprising that they are so suitable considering that they were designed to charge lead acid batteries....

Bye. Jasen

Reply to
Jasen

wasn't.

could

Someone tried to explain to me how to use a Delco 10S1 12 volt alternator by removing the voltage regulator, using external heat-sinked diodes, and using resistors to make an external regulator think that 48 volts was 12 volts and regulating accordingly. The problem I have with that idea is that I don't know what to do with the F and R tabs. One senses the battery voltage but I'm not sure which one, and then what to do with the other tab. I succeeded it getting about 30 volts output by putting a resistor in series with the F tab and Positive but it did not increase with speed. I have been told that if I do this right I can get about 63 amps @ 48 volts from my existing alternator. I've also been told the internal diodes will not withstand as much as 24 volts.

So far I understand how the 3-phase works, how to connect the diodes to both positive and negative, and probably how to remove the internal voltage regulator. I just don't understand the F and R terminals.

Thanks.

Reply to
Ulysses

I'm not familiar with that altenator, so I can't help with details there I did a quick google for Altenatoe 48V mod with no success,

Automotive Alternator Schematic on the other hand got me this one:

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which looks promising, you's need to change a few things for it to work on 48V though, mainly replacuing Z1 and Z2 with a combination of zener diodes that come closer to your target voltage. r3 and r4 should probably be increased to about 4 times the resistance, (eg:) 3.9K and 470K

a power resistor of upto three times the resistance of the altenator field winding winding resistance between tr4+r4 and DF+D3 might help too.

the transistors are kind of marginal too, a load dump at the wrong time would destroy them.

here's that schematic translated to ascii with zome of the components changed.

.--------------------+------------+---------------------- "48"V | | | \\ | | / 2.2K + | \\ / | / |< BC557 | +-----[1K]---+----| | | | |\\ | | | \\ / \\-+-\\ | + |< / \\ | || | | --. / \\ | | | T \\ --- |-| altenator | 1N4750 / 3.9K / \\ |\\| field | \\ T |-| winding | / | | | | | | `----------------------+-----------------+----------+------- 0V

the two 27v zener diodes put the switching point somewhere near 56v if that's too high use a different combination

the bc557 and BD902 transistors should probably be repaced with higher voltage versions, but I'm not sure what to rceccomend

the 3.9K resistor should be a 1W or larger it'll get hot.

--
Bye.
   Jasen
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Reply to
Jasen

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