Solar voltage effects on equipment 1

[guilio2010]

Will fluctuation in solar dc voltage cause failure in equipment even if the voltage is in spec? Ie, charging is at 28vdc and the days overcast causes the voltage to drop out to 25vdc and back up to 28 vdc throughout the day?

 

[VEBill]

If the power supply voltage applied to the equipment is within the specified limits for that equipment, it should not only not fail due to such input power supply voltage fluctuations (within the limits), but it should also meet all of its other technical and performance requirements at the same time.

That it will actually do so is a question best answered by reviewing the qualification test reports, and actual field results.

 

[guilio2010]

Your 2nd part is more right. If it is doing so. We have 2 separate systems running off the same power supply (batteries) but the one piece of equipment requires 12vdc so we have that being supplied by a dc dc converter while the other piece of equipment is running off 24vdc so it's voltage changes between 24ish to 28ish daily. The 24vdc system we are changing out and fixing so I'm looking at the design and was thinking maybe the power quality isn't as good as I thought it would have been.

 

[VEBill]

One could add a DC-DC Converter (or two in series if required) to effectively regulate the higher voltage supply. One would need to be cautious about efficiency, as adding additional converters will eat additional power. Solar systems often need to stay simple to remain within their solar power budget.

Or, one could dig into the unreliable system's circuits to see exactly why it's being fussy. Maybe there's just a single resistor value that needs a mod, or a simple tweak to the internal PS circuit, to make it work over a much wider range. 50/50 odds of this approach working, even if allowed.

 

[OperaHouse]

Under very light loading conditions a 24V array can easily go to to 44V. That high voltage can easily destroy some common switching regulator chips. that might be in the equipment. You haven't explained the basic charging circuit enough to comment further.

 

[IRstuff]

Seems to me that such behavior is really bad design.

TTFN
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[guilio2010]

Apparently the problems aren't as bad as it seems. From email it almost seemed like this was a daily event and when looking at it, it's not.

It's not a bad design but a design that needs refined to remove those thorns that are still present or that have come up. You can make the most elaborate design, consider all weather effects, all the maintenance, etc...but when the mother of all storms comes in, the once on 50 year storm, followed by subzero wind chills that haven't happened in the past 100 years for the area you planned on operating, you have to adapt. Again, I don't think it's a bad design, just refining it to fix the unexpected. But anyway....

The system has solar array going to a mppt charging controller, that ties into batteries, then to a load controller that then is distributed to our equipment. The charge controller is temperature compensated so we can see voltage spiking to ~30-32 vdc, but the equipment is speced for that kind of voltage within its safety aspects. The array voltage is converted to match the float battery voltage.

There are some areas that are repeat offenders so I'm going to focus on that. If it was a failure in equipment it should be across the board.

Thanks,

 

[racookpe1978]

Get a continuous recorder going for the ACTUAL dc voltage being thrown into the ckt over at least a 3 month period - preferably through the summer when on good days you'll see the highest voltage actually hitting the batteries. It easily could be 42 to 48 volts on a clear day around noon.

The low voltage out (24 volts) will most likely only cause less charge to go to the batteries, which will leave the systems vulnerable to discharging completely after 4 days of clouds.

 

[waross]

Use 24 Volt equipment designed for automotive use. Automotive equipment must withstand "load dump" events where the voltage on a nominal 12 Volt system may reach over 100 Volts.
Whenever the voltage gets much above the battery voltage there will be a voltage drop in the conductors from the solar array to the charge controller and from the charge controller to the batteries. Connecting the loads to the battery terminals rather than to the charge controller terminal will reduce to over voltage seen by the equipment.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[VEBill]

The system "...has solar array going to [highlight #FCE94F]a mppt charging controller[/highlight], that ties into batteries...", so hopefully the output of the system (at the batteries) is not going as high as "...42 to 48 volts on a clear day around noon."

If it was, then I think you'd smell the fried batteries.

 

[OperaHouse]

Solar is tough duty on batteries and I could easily see a battery become sulfated. That could result in battery voltage being quite high at fairly small charge currents. Some charge controllers rely heavily on the battery being a large capacity load. Could be this controller was purchased on price and from where some of the engineering is shady. My experience with solar is you never have enough panel capacity. Repeated deep discharges lead to battery destruction.

 

[guilio2010]

We have a good charge controller. Nothing shady or ebay or alibaba type. Our system is 24v nominal. The max voltage we will see is ~ 31v on cold days with temp composition. I feel confident that we have a good solar system.

I think the one issues I am seeing more is rs485 channels going out so I'm thinking

 

[guilio2010]

Sorry. Accidentally hit post.

I think with our comms channels going out on the 485 that the higher voltage may be contributing to that. The only thing that doesn't make sense though is on one piece of equipment we have a optical isolator on the 485 so I wouldn't think that could carry over. May have to set up a daq system to log that if possible.

 

[IRstuff]

Do you see a higher failure rate when switching the equipment on/off? RS-4xx receivers are VERY intolerant of common mode input voltages, so TX/RX on different power supplies can lead to problems, although, the optos should protect your receivers from damage.

TTFN
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[guilio2010]

Actually, I never thought about that. Our one system we are communicating with is on 12vdc regulated and the Plc we keep losing 485 on is off unregulated 24vdc power. We did switch the Plc to 12vdc regulated cause my thought process was concerned with the unregulated power maybe spiking causing the problem.

What is he 485 voltage range based on power input?

 

[IRstuff]

A classical TTL RS-4xx receiver has something like Vss - 7V to VCC + 7V. Other technology families have better common mode immunity.

TTFN
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