Using a KID as a DC UPS?

[GlueGuy]

We run a small wireless internet company, and have several solar-powered sites.  We have several more AC-powered sites.

Because all of our equipment runs on either 24V or 48V DC, we don't use conventional UPS devices.  Instead, we use "smart chargers", that usually run in float 24x7.

The advantage of this is that we gain a lot of efficiency because we are not converting to/from AC/DC a couple of times.

The disadvantage of this approach is that (1) there is no built-in LVD, and (2) There is no battery conditioning or anything beyond a very simple 2-stage charging.

So I am wondering if it would be feasable to use a KID as a "smarter" charger?

The basic idea would be to rectify/filter straight AC into the PV/wind input terminals, and let the KID do its thing.

Would I need to attenuate the rectified/filtered AC (P-P voltage on straight 110 is close to 170 volts)?

Other issues?

[mtdoc]

I would think you'd want to use a transformer to isolate and step down the voltage before rectifying it.  I'm not sure if there are other issues to consider.

[tecnodave]

Glue Guy,

One other thing you might want to do is put a resistor between the power source and the kid, and definitely use a step down isolation transformer for safety and maybe some filtering in there to cut down on the ripple. The kid and all MPPT controllers will try to pull the voltage down to find the "sweet spot" where the power source will produce the most power. A fixed power supply will not allow the controller to do this hense the resistor to allow that.......ops there goes your effiency!


Are you glue guy from Slavegate in Scott's Valley?   Hi,  I'm David from the calibration labs and failure analysis


td

[Vic]

Agree with mtdoc,  that you will want a transformer to setp-down the AC voltage,  AND provide isolation for safety.  You will want the rectified DC voltage to be about two times the nominal battery voltage or a bit less,  under load.

The resistor may be needed,  but for the KID,  you probably want to use O&P mode,  instead of Solar.

We have done something similar with the KID,  on occasion,  using a Switch-Mode DC PS as the source of power.

Some folks at MidNite  have not wholeheartedly-endorsed this general approach (from recollection).

FWIW,  Vic

[GlueGuy]

I got some nice emails from Midnite tech support, and you are right.  First, just rectifying straight AC will end up with  a peak voltage in the neighborhood of 190 volts.  So at least stepping down would be necessary.

The second issue is that a straight unregulated, or lightly power supply would be too "hard", and might easily go over the 30 amp current limit for the KID.

So if we go through with this, we will use a higher-end power supply in the 50-60 volt range with built-in current limiting.  This will "soften" the voltage coming from the power supply, and hopefully protect the KID from going over it's current limit.

[GlueGuy]

Are you glue guy from Slavegate in Scott's Valley?   Hi,  I'm David from the calibration labs and failure analysis
td

No, but not too far from there.  We get our trash picked up from a small outfit in Boulder Creek (just down the road from Scott's Valley).

[tecnodave]

GlueGuy,

I was referring to Seagate Technology in Scott's Valley. They had an adhesives department and the head guy was GlueGuy. We were all Seaslaves for Slavegate. Inside joke, they worked us into the ground. I still have burnout from that place.

td

[GlueGuy]

Sorry I missed the inside joke.

I built a fiberglass airplane once upon a time.  Learned a lot about epoxies, resins, etc.  Plus worked in silicon valley doing all kinds of hardware/software integration projects.  GlueGuy became my nom de plum in a manner of speaking.