Can you charge a battery from two sources at the same time?

[BobG]

Lets say we have a nice windy and sunny day and some discharged
batteries. Lets say 11V. I hook up the pv charge controller, its
putting out whatever V it thinks is getting max power. Lets say its
14V. Now the microcontroller on the wind turbine charge controller
sees 14V, and either thinks the battery is charged, or tries to hump
out 16V or so to try to get some amps into the rig, but this would
confuse the mppt pv controller. So is there an algorithm or strategy
for using two different charging sources at the same time? Have two
big watt low ohm mixing resistors, like mixing audio? Heating Rs
doesnt sound thrifty.

 

[Tom Biasi]

"BobG" <bobgardner@aol.com> wrote in message
news:03f0e2aa-d015-489d-afeb-18c3e82baa32@p69g2000hsa.googlegroups.com...

Lets say we have a nice windy and sunny day and some discharged
batteries. Lets say 11V. I hook up the pv charge controller, its
putting out whatever V it thinks is getting max power. Lets say its
14V. Now the microcontroller on the wind turbine charge controller
sees 14V, and either thinks the battery is charged, or tries to hump
out 16V or so to try to get some amps into the rig, but this would
confuse the mppt pv controller. So is there an algorithm or strategy
for using two different charging sources at the same time? Have two
big watt low ohm mixing resistors, like mixing audio? Heating Rs
doesnt sound thrifty.

You are describing more than one issue.
Yes you can charge a battery from multiple sources provided the sources are
isolated from each other. In you example a simple diode would most likely do
the trick.
The individual regulation of each charging system would be a function of
that system.
You may also need to supply a sense signal to the chargers separately.
Tom

 

[Rich Grise]

On Fri, 21 Dec 2007 14:13:18 -0800, BobG wrote:

Lets say we have a nice windy and sunny day and some discharged
batteries. Lets say 11V. I hook up the pv charge controller, its putting
out whatever V it thinks is getting max power. Lets say its 14V. Now the
microcontroller on the wind turbine charge controller sees 14V, and
either thinks the battery is charged, or tries to hump out 16V or so to
try to get some amps into the rig, but this would confuse the mppt pv
controller. So is there an algorithm or strategy for using two different
charging sources at the same time? Have two big watt low ohm mixing
resistors, like mixing audio? Heating Rs doesnt sound thrifty.

Sense the two currents, and design a controller that will adjust
them both to share the load. You'll have to come up with an
algorithm, but conceptually it's like a mixer - two inputs and
one output. You know what the output needs, and each of the
inputs has a certain capacity. You could run them both wide
open and just limit them by looking at its input current
vs. the output spec, and send it a "not so much" signal.
You'd do that to the other one simultaneously, and you'd
have to decide how you want to write the algorithm (or design
the circuit =:-O ) to do the sharing the way you want it.

Then again, you could just run the solar wide open (as long
as it's voltage-limited) and regulate the charging current
from the windmill, either by feathering the blades, or finding
someplace else to dump the power, like into the house or
the grid. ;-)

Of course, you'd need to include the charge controller, to say
"OK, Enough!" when it is. Then you'll have to just let all
of that energy lie there. )-; Or get more batteries for Xmas. ;-)

Have Fun!
Rich

 

[John Fields]

On Fri, 21 Dec 2007 14:13:18 -0800 (PST), BobG <bobgardner@aol.com>
wrote:

Lets say we have a nice windy and sunny day and some discharged
batteries. Lets say 11V. I hook up the pv charge controller, its
putting out whatever V it thinks is getting max power. Lets say its
14V. Now the microcontroller on the wind turbine charge controller
sees 14V, and either thinks the battery is charged, or tries to hump
out 16V or so to try to get some amps into the rig, but this would
confuse the mppt pv controller. So is there an algorithm or strategy
for using two different charging sources at the same time? Have two
big watt low ohm mixing resistors, like mixing audio? Heating Rs
doesnt sound thrifty.

---
If you have two sources which are both capable of charging your
batteries, and they're both hot, and you know the maximum charge
current allowed into your batteries, choose the source which will
waste the least energy.


--
JF

 

[Bob Monsen]

"BobG" <bobgardner@aol.com> wrote in message
news:03f0e2aa-d015-489d-afeb-18c3e82baa32@p69g2000hsa.googlegroups.com...

Lets say we have a nice windy and sunny day and some discharged
batteries. Lets say 11V. I hook up the pv charge controller, its
putting out whatever V it thinks is getting max power. Lets say its
14V. Now the microcontroller on the wind turbine charge controller
sees 14V, and either thinks the battery is charged, or tries to hump
out 16V or so to try to get some amps into the rig, but this would
confuse the mppt pv controller. So is there an algorithm or strategy
for using two different charging sources at the same time? Have two
big watt low ohm mixing resistors, like mixing audio? Heating Rs
doesnt sound thrifty.

If these are lead acid battery controllers, then the controllers will
probably first try to limit current, then maintain a constant cell voltage.
After this, they may or may not drop the voltage a bit for a 'float' phase.

If you use both through diodes, and they both measure the current
separately, then you'll end up with twice the current, which could overheat
the battery. After they charge the batteries too quickly, they will then
attempt to keep the voltage too low, because of the diode drop on the
output. So, it'll work, but not very well.

If your controllers could measure the total current rather than their
contribution, then they would be able to share the load. If they measured
voltage at the battery, rather than at the output of the controller, they
could also deal with the saturated phase of charging properly by decreasing
the current to maintain the voltage. I'm not sure how this would work for
the float phase.

To make this work, you would probably need to figure out how the controllers
measure current and voltage, and manipulate the inputs somehow. Having a
single controller that handled all of this would be the optimal solution.

These guys claim to have figured it out:

http://www.solarseller.com/flexcharge_wind_hydro_solar_charge_controllers.htm

Regards,
Bob Monsen