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'[EE] Charging a 120V Battery Bank : PFC ?'
2009\03\26@015320 by

Hi happens that I find the piclist to be the community of the fittest
electronic engineers that I know on the web, that's why I ask here and not
on some of grid living list...

I may have mentioned before that I use 10 pc. 12V car batteries at my of
grid ranch, and that I charge those using a simple rectifier, either Bridge
from 120V AC or 2 diodes using half of each of the 2 120V outlets around the
center of my generators 240 V AC output (I do that to reduce the chance of
any one of the automatic breakers of the 2 120V circuits from tripping).

This seems to work quite good, but I just read that it is not advisable to
charge Car batteries on pulse current, and since they would be charged only
when the generators output voltage reaches above their current charge
voltage, it definitely is pulse...

So I have been toying with the idea to try a different circuit, and I would
like some comments and hints on dimensioning the circuit!
=== here it goes ===

If I use a circuit like they use on computer power supplies that double the
voltage using 2 diodes and 2 Capacitors, but hooked it up to the battery
bank, the capacitors would have to discharge completely every cycle (maybe
even reverse polarity, which I could prevent with another diode per cap),
but since last half waves capacitor starts out with minimally the voltage of
the bank, the new half wave charging the next capacitor would push up that
voltage and therefore start discharging the Cap to the Battery starting from
0...

I know it may be difficult to describe in words, but its a simple enough
drawing!
I wonder though would kind of capacitors would stand this type of abuse and
how I would estimate the current that would be required?
I figure there must be a possibility to develop a formula using the Coulombs
at max voltage, and then average out this number of electrons over the cycle
to get an estimate for the produced, now less 'uncontiniously' pulsing!

Thanks for any hints or help to express this better so more responses are
possible!

--
Tobias Gogolin
skype: moontogo
messenger: usertogohotmail.com

You develop Sustainable Ranch Technology at
http://tech.groups.yahoo.com/group/SURA-TECH
an Open Source Electric Motor/Alternator at
groups.yahoo.com/group/Performance_Axial_Flux
and an Open Source Motor Controller at http://groups.yahoo.com/group/GoBox
2009/3/26 Tobias Gogolin <usertogogmail.com>:
{Quote hidden}

> -
rn Thu, Mar 26, 2009 at 01:53:19AM -0400, Tobias Gogolin wrote:
> Hi happens that I find the piclist to be the community of the fittest
> electronic engineers that I know on the web, that's why I ask here and not
> on some of grid living list...
>
> I may have mentioned before that I use 10 pc. 12V car batteries at my of
> grid ranch, and that I charge those using a simple rectifier, either Bridge
> from 120V AC or 2 diodes using half of each of the 2 120V outlets around the
> center of my generators 240 V AC output (I do that to reduce the chance of
> any one of the automatic breakers of the 2 120V circuits from tripping).

>
> This seems to work quite good, but I just read that it is not advisable to
> charge Car batteries on pulse current, and since they would be charged only
> when the generators output voltage reaches above their current charge
> voltage, it definitely is pulse...

I saw the term 'car battery' and an alarm went off in my head. What exactly
is your application? The reason that I ask is that car batteries are
specifically constructed for a single application: deliver a large amount
of power in a short timeframe (starting) and then expect to be immediately
recharged. They are not good for other applications such as delivering
steady power for long periods of time. Batteries for that application are
called deep cycle batteries. Just a heads up.

As for charging, this is a common problem in the electric vechicle world
because an EV main pack would be contructed quite similarly to the pack you
described. The circuit that you described above is called a Bad Boy
charger, and you've described some of the problems with it including
tripping breakers and poor power factor correction. Several improved, and
more importantly safer, circuits are outlined here:

http://www.evalbum.com/tech

Specifically take a look at the Bonn charger circuit described by Lee Hart.

Hope this helps,

BAJ
On 3/25/09, Tobias Gogolin <usertogogmail.com> wrote:
> Hi happens that I find the piclist to be the community of the fittest
> electronic engineers that I know on the web, that's why I ask here and not
> on some of grid living list...
>
> I may have mentioned before that I use 10 pc. 12V car batteries at my of
> grid ranch, and that I charge those using a simple rectifier, either Bridge
> from 120V AC or 2 diodes using half of each of the 2 120V outlets around the
> center of my generators 240 V AC output (I do that to reduce the chance of
> any one of the automatic breakers of the 2 120V circuits from tripping).
>
> This seems to work quite good, but I just read that it is not advisable to
> charge Car batteries on pulse current,

Maybe you should start first by defining the amount o energy you need
for charging.
Assuming your car batteries have say 44Ah (but could also have 80Ah as
well) if you need to fast charge those batteries, you will need 140V
and 4...10A. I don't know where you read that is not advisable to
charge acid Pb batteries with pulse current, but you probably know
that a car battery acts like a huge capacitor. As long the charging
current is less than 10% of the battery nominal current and the
maximum voltage per one battery is less than 14V at full charge , it's
fine with current pulse charging.

Vasile
Why not use a phase angle control method with a DC choke (its the same way
as most industrial charging systems work) where you have two diodes and two
thyristors to form a full wave bridge. This way you can sample the DC
voltage and control the voltage supplied to the battery and hence provide a
continuous trickle charge if required.

Steve

{Original Message removed}
Thanks Jeff,

I dislike the circuits a bit because of the need for transformers!
And a rough estimate by Farday's law; if 1 Farad is delivering one Ampere
for one Second  if it was charged with one Volt (right?), then:

lets say 1000uF = 1 mF = one Thousands F but with 100 times the voltage and
in a hundredth of the time should get me into the 10 A Range ~ right?

Of course I will have to calculate using the internal resistance of the
capacitors how much Wattage would be lost in the caps and if the would get
hot, Maybe they could each get an individual water bath?

On Thu, Mar 26, 2009 at 6:02 AM, Byron Jeff <byronjeffclayton.edu> wrote:

{Quote hidden}

Thanks Vasile !

Yes they are 44Ah, and my DMM says I reach more than 3A even if I charge all
10 of them in series, sometimes however they do get above 14V

I found the note about pulse charging at a site that said battery University
I think, I was looking into selecting replacement Batteries for my 36V
E-Bike, but it might be that this comes form people that want to sell
chargers...

By the way how do I know my 'battery nominal current' ?

My usual discharge is minute, a few energy saving light bulbs that draw
~210mA each or rarely a vacuum or a angle grinder, and the standby mode
Rabbit protection electrifying my cages against ground so the dogs know I'm
serious!

The other day I did my first battery based welding, (which is excellent)
using 2 parallel Banks of 3 Batteries in series (36V)!

On Thu, Mar 26, 2009 at 10:03 AM, Vasile Surducan <piclist9gmail.com>wrote:

{Quote hidden}

> -
>car batteries are
>specifically constructed for a single application: deliver a large amount
>of power in a short timeframe (starting) and then expect to be immediately
>recharged.
Its true they are designed to handle that, not that they like it but they
learned to deal with it...

>They are not good for other applications such as delivering
>steady power for long periods of time. Batteries for that application are
>called deep cycle batteries.

Well they are able to be in standby without much draw for quite extended
periods of time...

I make it a point to neither charge my Batteries to the top, nor to
discharge them much, it would have been some kind of mishap if my batteries
had been discharged below half in the year they are in service...

I'm curious how long they will hold out!
I know that the thin plates and the retention of some kind of paste is the
issue about car batteries not being able to hold out for as long, but also
figure they cost a third of deep cycle batteries, and I had not time for
opening a savings account...

On Thu, Mar 26, 2009 at 6:02 AM, Byron Jeff <byronjeffclayton.edu> wrote:

{Quote hidden}

> -

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