# Ideas For 675 Ah 48 volt Battery Bank Charger?

Discussion in 'Electronic Basics' started by Ulysses, Jun 22, 2007.

1. ### UlyssesGuest

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.

2. ### BobGGuest

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)

3. ### JasenGuest

You want plans for a 6KW charger ?
AFAIK no capacitor is needed.
that's news to me.

A big inductor might work better.

Bye.
Jasen

4. ### UlyssesGuest

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.

5. ### UlyssesGuest

I like that idea. Thanks.

6. ### JasenGuest

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

7. ### UlyssesGuest

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.

8. ### JasenGuest

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:

http://homepage.sunrise.ch/mysunrise/joerg.hau/mot/voltreg.htm

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 +---||--+-+----| |\ BD902
| 1N4750 | || | |\ \
| | 150nF | \___|
| | | |
\---\ +---------|--[470K]--+--R?--+------> --.
/ \ | | |
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.

9. ### UlyssesGuest

Great. thanks!

10. ### John PopelishGuest

If the alternator was wound for 12 volts, and this regulator
goes full on, for any reason from failure to slightly low
battery voltage, the alternator field will be quickly fried,
of something else doesn't burn out first.

I think it would be much easier to start over and make a
crude switching regulator with a 0 to 14 volt output to feed
the field coil, with the output voltage determined by the
error in the 48 volt battery voltage.

11. ### neon

1,325
0
Oct 21, 2006
the transformer to 60 v is easy to implement efficiency about probably 80 85% why a cap batery love pulseting dc for charging. i would recomend a current limiting thought. 100 amps 48 vthat 4800watts that is a lot of heat battery do not like heat