Electronics Question: DC power supply into a PWM solar charge controller.

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wipe_out

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I have a PWM solar charge controller with a small solar panel.. I also have an old laptop power supply that puts out 19v DC up to 6A.. The charge controller can take up to 30v DC and 16A.. So as a way to boost the battery charging I have tried connected the laptop power supply to the solar charge controller.. Using a DC watt meter it all seems to work well and I get up to 100W of charging..

The concerns I have are that the power supply makes a buzzing sound which I guess is due to the PWM switching of the charge controller and also the power supply gets quite warm, bordering on hot..

So the question for the electronics people out there.. Is a laptop power supply safe to use for is this type of application or is it not suitable due to the PWM switching?

Thanks
 
wipe_out said:
I have a PWM solar charge controller with a small solar panel.. I also have an old laptop power supply that puts out 19v DC up to 6A.. The charge controller can take up to 30v DC and 16A.. So as a way to boost the battery charging I have tried connected the laptop power supply to the solar charge controller.. Using a DC watt meter it all seems to work well and I get up to 100W of charging..

The concerns I have are that the power supply makes a buzzing sound which I guess is due to the PWM switching of the charge controller and also the power supply gets quite warm, bordering on hot..

So the question for the electronics people out there.. Is a laptop power supply safe to use for is this type of application or is it not suitable due to the PWM switching?

Thanks
Click to expand...

You're overloading the psu (the fact its getting hot and buzzing tells you that) so watch out it doesn't catch fire (clone psus particularly)

Also, a pwm controller connects the laptop psu directly to the battery for a variable length of time (the Pulse Width) so depending on how discharged the battery is, the result is much too high a current demand from the psu.
If you are getting 100w average charging, this implies around 7.7amps at 13v battery voltage, so would explain the overload. (even if the battery voltage was 14v, 100w is still over 7amps) The peak current will be even higher so pity the poor power supply!
 
ianj99 said:
You're overloading the psu (the fact its getting hot and buzzing tells you that) so watch out it doesn't catch fire (clone psus particularly)

Also, a pwm controller connects the laptop psu directly to the battery for a variable length of time (the Pulse Width) so depending on how discharged the battery is, the result is much too high a current demand from the psu.
If you are getting 100w average charging, this implies around 7.7amps at 13v battery voltage, so would explain the overload. (even if the battery voltage was 14v, 100w is still over 7amps) The peak current will be even higher so pity the poor power supply!
Click to expand...

That's kind of what I thought just wanted to check.. When the battery is not that empty the charging drops to about 50w but the PSU is still quite warm.. The 100w is the peak when the battery is quite flat.. Seemed like a good idea since I had the PSU already but I guess its not the right application for it..
 
You could make it happier by putting a chunky capacitor across the output of the PSU. I imagine it gets quite narked at the stop/start nature of the load (PWM controller) a capacitor will give it something to do while the PWM is off.
 
You may have more subtle problems than overloading.
Your PWM controller is varying the load on the PSU searching for the best power, then using a control loop to hold that load point.
Meanwhile the PSU is using a similar control loop to attempt to hold a steady voltage, hopefully with a current limit.
The net effect might be that the PWM controller is driving the PSU into current limit many times a second, or even causing the PSU to oscillate as the two control loops fight each other.
This may explain why it's still not happy when the power drops to 50W.
Some resistance between the two (and /or a fat capacitor to ground) might sort it out, but it sounds more like a development challenge for someone with a scope and detailed knowledge of the two circuits TBH.

A current limited step-down converter, limited to safely under the PSU's rating might be a better bet than the PWM rated at 30A.
 
wipe_out said:
No reason, just had the PSU and solar controller already so figured it maybe a way to have both mains charging and solar charging from the same device for free.. :)
Click to expand...

Your main problem is that the output impedance of the PSU is much lower than a solar panel. A solar panel will self limit the current flow in an output short condition where as a typical PSU continues to drive current until something fails. If you are lucky it will be a fuse.

In a crude battery charger you will have a current limiting resistor.

I charge various NiMh and NiCad batteries from a DC-DC converter with a current limiting resistor. I just have to manually time the charging to prevent over charging the battery.
 
ianj99 said:
If you are getting 100w average charging, this implies around 7.7amps at 13v battery voltage, so would explain the overload.
Click to expand...

But only 5.3 at the 19v that the PSU is putting out, which is within its rating.

I'm not an electronics expert, but I like lw395's explanation - both devices do their thing by switching rapidly on and off in response to what's on the wire, and probably confuse each other.

Pete
 
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