question

kwagga avatar image
kwagga asked

Connecting PSU to PWM for additional power?

Hey Guys,

I'm having an issue where for several days at a time, my 12v DC system (powering a gate and alarm system) isn't receiving enough solar energy to charge and maintain my battery system. More batteries, isn't an option.


For day to day, my 50w Solar Panel connected to a BlueSolar 12v 5A PWM does just fine in topping off the 24Ah battery and keeping it healthy, we've now had 7 days of continuous rain, and the system stopped working. I have now connected a 5A battery charger directly to the battery pack to get it working again, and while this works, I fear the batteries might be overcharged/damaged in the long run since once the sun comes out again, there'll be two power sources.


I was thinking, what if I connect a 15v (13.5V ~ 18V, centered around 15 volt) regulated power supply in conjunction with the solar panel into the PWM, since the PWM will still do bulk, float and disconnect.

While I've read that "stiff" power supplies are a bad idea, the power supply I'm thinking of, is a Mean Well HDR-series, which offers "complete protection" with it's hiccup-ability - it has short circuit, overload (constant current), and over-voltage protection. The BlueSolar PWM additionally offers protection against over current and short circuit also.

The Solar Panel has an open circuit voltage of 21V - So I don't think connecting a DC power supply will damage it?

PSU in question: https://docs.rs-online.com/ba86/0900766b815d941d.pdf

PWM in question: https://www.victronenergy.com/upload/documents/Manual-BlueSolar-PWM-Light-12-24V-Charge-Controller-EN-A4.pdf


Am I correct in saying while the PWM doesn't regulate the actual voltage, it only passes it through like a switch, unlike a MPPT - which actively corrects/regulates voltage and current.

The only problem I foresee, is that the PWM is rated to 5 amps, so if the PV panel comes online to full strength (2.9A) and the PSU (4A) that'll be too much for the PWM to handle. - Which I can mitigate by connecting the PSU to a day-night switch to prevent overload.


So my question is, will this work -and work well?


My question is similar to one posted here, but is for a PWM and not a MPPT, and also not a bench power supply:

https://community.victronenergy.com/questions/16668/use-of-a-bench-dc-power-supply-as-pv-input-to-a-sm.html

If all of this works, it'll also reduce the cycle-use of the batteries, which will be great.




BlueSolar PWM
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2 Answers
kwagga avatar image
kwagga answered ·

To answer my own question, tried this with a CTEK MXS 5.0.


After about 3 months of operation the CTEK unexpectedly failed. The symptom of the unit was, it would get "stuck" on Step/LED 5 - check. After power cycling the unit, it wouldn't charge.


So to summarize, this isn't a good idea.

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kwagga avatar image
kwagga answered ·

In case anyone wants to know, we can't purely rely on grid power, since that's unreliable also. But there's always one or the other (Sun vs AC Supply)

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