charger with constant current

L

lerameur

Guest
Hello,

I am attempting to charge a battery and I would like to have a
feedback on the approach.
I have a 18v supply coming from a generator and want to charge a 12v
battery.
First I cannot constant charge the 12v battery at that potential.
Second I though of building a sort of pulse charger so I can charge
the 12v battery with lets say 18v or even higher with pulses.
Therefore I decided to make a boost converter, therefore 18v to the
converter outputs about 55v.
Third, the problem with step 2 above is that the current stop flowing
through the inductor of my boost converter, I have a three amp current
from the generator which I do not want to decrease or stop. I also get
over 17v at the batteries.. which I stopped immediately.

Is this a question of timing, or should I approach the problem in a
totally different way.?

ken
 
On Sun, 27 Jul 2008 09:49:59 -0700 (PDT), lerameur
<lerameur@yahoo.com> wrote:

Hello,

I am attempting to charge a battery and I would like to have a
feedback on the approach.
I have a 18v supply coming from a generator and want to charge a 12v
battery.
First I cannot constant charge the 12v battery at that potential.
Click to expand...
---
Why not?

As long as the regulator can dissipate the power which it'll develop
with the voltage across it and the current through it there should be
no problem.
---

Second I though of building a sort of pulse charger so I can charge
the 12v battery with lets say 18v or even higher with pulses.
Therefore I decided to make a boost converter, therefore 18v to the
converter outputs about 55v.
Third, the problem with step 2 above is that the current stop flowing
through the inductor of my boost converter, I have a three amp current
from the generator which I do not want to decrease or stop. I also get
over 17v at the batteries.. which I stopped immediately.

Is this a question of timing, or should I approach the problem in a
totally different way.
Click to expand...
---
Depends...

What kind of a battery is it and how much current do you want to pump
into it?


JF
 
lerameur wrote:
Hello,

I am attempting to charge a battery and I would like to have a
feedback on the approach.
I have a 18v supply coming from a generator and want to charge a 12v
battery.
First I cannot constant charge the 12v battery at that potential.
Second I though of building a sort of pulse charger so I can charge
the 12v battery with lets say 18v or even higher with pulses.
Therefore I decided to make a boost converter, therefore 18v to the
converter outputs about 55v.
Third, the problem with step 2 above is that the current stop flowing
through the inductor of my boost converter, I have a three amp current
from the generator which I do not want to decrease or stop. I also get
over 17v at the batteries.. which I stopped immediately.

Is this a question of timing, or should I approach the problem in a
totally different way.?

ken
Click to expand...
You should approach the problem in a totally different way. Mostly by
deciding what you need and pursuing it, instead of flopping around
trying this and that and the other thing and wondering what's going wrong.

First, you should think about the battery chemistry. Since you didn't
mention it, I assume you're not thinking hard about it. If you have a
6-cell lead-acid battery, then you almost certainly want a constant
voltage charger, or a current-limited constant voltage charger. If
you're charging a 10-cell NiCd pack then you can get by with a constant
current; if you're charging a 10-cell NiMH pack then you probably want a
constant current with peak detection, or a _really_ low current constant
current charger and an acceptance of reduced battery life.

Once you've figured out what battery chemistry you're dealing with you
should look to the flavor of battery that you're using -- automotive
batteries have slightly different requirements than sealed lead-acid,
high-capacity NiCds often can't be charged as fast as high-current ones,
etc.

Get yourself a copy of "Rechargeable Batteries Applications Handbook",
it discusses chemistries and charging methods (although it was written
before Li-Ion and Li-Po batteries came along, so you're on your own with
those).

Finally, once you know what the charger _should_ do, _then_ start
thinking about how to make it do the right thing.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
 
lerameur wrote:
On Jul 27, 2:57 pm, Tim Wescott <t...@seemywebsite.com> wrote:
lerameur wrote:
Hello,
I am attempting to charge a battery and I would like to have a
feedback on the approach.
I have a 18v supply coming from a generator and want to charge a 12v
battery.
First I cannot constant charge the 12v battery at that potential.
Second I though of building a sort of pulse charger so I can charge
the 12v battery with lets say 18v or even higher with pulses.
Therefore I decided to make a boost converter, therefore 18v to the
converter outputs about 55v.
Third, the problem with step 2 above is that the current stop flowing
through the inductor of my boost converter, I have a three amp current
from the generator which I do not want to decrease or stop. I also get
over 17v at the batteries.. which I stopped immediately.
Is this a question of timing, or should I approach the problem in a
totally different way.?
ken
You should approach the problem in a totally different way. Mostly by
deciding what you need and pursuing it, instead of flopping around
trying this and that and the other thing and wondering what's going wrong.

First, you should think about the battery chemistry. Since you didn't
mention it, I assume you're not thinking hard about it. If you have a
6-cell lead-acid battery, then you almost certainly want a constant
voltage charger, or a current-limited constant voltage charger. If
you're charging a 10-cell NiCd pack then you can get by with a constant
current; if you're charging a 10-cell NiMH pack then you probably want a
constant current with peak detection, or a _really_ low current constant
current charger and an acceptance of reduced battery life.

Once you've figured out what battery chemistry you're dealing with you
should look to the flavor of battery that you're using -- automotive
batteries have slightly different requirements than sealed lead-acid,
high-capacity NiCds often can't be charged as fast as high-current ones,
etc.

Get yourself a copy of "Rechargeable Batteries Applications Handbook",
it discusses chemistries and charging methods (although it was written
before Li-Ion and Li-Po batteries came along, so you're on your own with
those).

Finally, once you know what the charger _should_ do, _then_ start
thinking about how to make it do the right thing.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details athttp://www.wescottdesign.com/actfes/actfes.html

Hi,

I am using a 12v sealed lead acid battery (being charge).
My aim is to charge this battery then the circuit will charge a
second 12v battery. Yes I want to do this way.
I have a Pic chip that determines the battery voltage and transfer the
charging to the desired battery.
the problem now is that the pic chip sees a fully charged battery when
in fact it only begun charging.
The reason for pulse charging, I read it was better for batteries..
nevertheless, my pulse charging seems not to be working as it sees the
maximum charge at the pole of the battery. How do they do it so that
the battery only retains the average voltage on the charging battery..

K
Click to expand...
Detecting the state of charge of a battery from it's terminal voltage
alone is just about impossible. You can have a near-death cell that,
when you give it a rest and measure it with a high-impedance meter, will
read full charge.

Your best bet at detecting charge would be to look at the current that
goes into the battery when it's getting its constant-voltage charge --
current below some threshold indicates that the battery is charged.

When you're all done charging both batteries, you probably want to put
them on a float charge.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
 
On Jul 27, 2:57 pm, Tim Wescott <t...@seemywebsite.com> wrote:
lerameur wrote:
Hello,

I am attempting to charge a battery and I would like to have a
feedback on the approach.
I have a 18v supply coming from a generator and want to charge a 12v
battery.
First I cannot constant charge the 12v battery at that potential.
Second I though of building a sort of pulse charger so I can charge
the 12v battery with lets say 18v or even higher with pulses.
Therefore I decided to make a boost converter, therefore 18v to the
converter outputs about 55v.
Third, the problem with step 2 above is that the current stop flowing
through the inductor of my boost converter, I have a three amp current
from the generator which I do not want to decrease or stop. I also get
over 17v at the batteries.. which I stopped immediately.

Is this a question of timing, or should I approach the problem in a
totally different way.?

ken

You should approach the problem in a totally different way. Mostly by
deciding what you need and pursuing it, instead of flopping around
trying this and that and the other thing and wondering what's going wrong.

First, you should think about the battery chemistry. Since you didn't
mention it, I assume you're not thinking hard about it. If you have a
6-cell lead-acid battery, then you almost certainly want a constant
voltage charger, or a current-limited constant voltage charger. If
you're charging a 10-cell NiCd pack then you can get by with a constant
current; if you're charging a 10-cell NiMH pack then you probably want a
constant current with peak detection, or a _really_ low current constant
current charger and an acceptance of reduced battery life.

Once you've figured out what battery chemistry you're dealing with you
should look to the flavor of battery that you're using -- automotive
batteries have slightly different requirements than sealed lead-acid,
high-capacity NiCds often can't be charged as fast as high-current ones,
etc.

Get yourself a copy of "Rechargeable Batteries Applications Handbook",
it discusses chemistries and charging methods (although it was written
before Li-Ion and Li-Po batteries came along, so you're on your own with
those).

Finally, once you know what the charger _should_ do, _then_ start
thinking about how to make it do the right thing.

--

Tim Wescott
Wescott Design Serviceshttp://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details athttp://www.wescottdesign.com/actfes/actfes.html
Click to expand...
Hi,

I am using a 12v sealed lead acid battery (being charge).
My aim is to charge this battery then the circuit will charge a
second 12v battery. Yes I want to do this way.
I have a Pic chip that determines the battery voltage and transfer the
charging to the desired battery.
the problem now is that the pic chip sees a fully charged battery when
in fact it only begun charging.
The reason for pulse charging, I read it was better for batteries..
nevertheless, my pulse charging seems not to be working as it sees the
maximum charge at the pole of the battery. How do they do it so that
the battery only retains the average voltage on the charging battery..

K
 
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