Common sense failure

Hmm, I'm seeing a thread on using DC into a VFD to run an AC motor in a trolley at that link. I read all the posts and see DC-AC but don't see UPS mentioned or pick up the concept of it anywhere in the text. Nope, not in the previous or next thread, either. Are you -that- much smarter than me, did you post the wrong link, or did I miss something?

Reply to
Larry Jaques
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Although opposition to power grid improvement is strong here we haven't yet reached the brownout stage, our outages are from storms or traffic accidents.

My computers (=TVs) are all laptops with fairly decent batteries and the APC1400 UPS can protect them while doing large video file backups, as well as run the fridge ovenight. My homebrew UPS works for the Alpicool freezer. This meter is due to arrive today and will give me terminal screws to better arrange the junction of four wire pairs that's currently skywired and taped.

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I also ordered USB breakout boards

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and 18 + 22 AWG flexible Silicone wire to connect the meter shunt bases to their displays more reliably.

They shut off the power during a brownout and wait 3 minutes for the pressure to drop before turning it back on.

The 20l Alpi fits my needs only because I've learned to live with a

45l fridge. I would have bought a larger one if Amazon offered it. It does fit neatly in the back of the SUV beside the 12V outlet and holds a typical shopping load.

The problem is that if a 100A meter is accurate to 1%, the Amp-hour total it gives for the battery will be very uncertain for low charge and discharge currents. I want to -know- that the battery has enough charge left to last overnight.

Voltage isn't a reliable indicator when the battery is cycling. The battery that has been running the Alpi since last evening reads 11.76V On, 12.135V Off, and is still rising when the freezer cycles On again. Some of that drop is in the temporary wiring and meter shunt.

The Yeeco 100V 15A meter isn't accurate to the last digit(s) but the internal noise is low enough that it shows the rate of voltage droop or recovery very smoothly, with no jitter. Current is noisier, which could be due to the Alpi's switching supply. I can estimate how far along the voltage is on the recovery curve by the time to rise 1 milliVolt. Now I need a stable, low noise variable current source to calibrate my ammeters with the benchtop Flukes. I have a lot of older tabbed 18650s that I need to sort by remaining capacity before rebuilding batteries with them.

-jsw

Reply to
Jim Wilkins

Batteries could supply the DC to run the VFD. Keeping them charged is easy. The idea might be practical IF you happen onto a suitable VFD for cheap and have enough batteries. I happened onto a repairable

1400VA pure sine UPS for free instead.

-jsw

Reply to
Jim Wilkins

Here's another interesting idea:

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He uses a Prius along with an inverter to power his entire house.

Reply to
rangerssuck

The best part: it lets me keep ICE CREAM!

-jsw

Reply to
Jim Wilkins

Ours here is like that, too.

I saw the female micro version of those and got some to use with cables a while back. Ten for $0.77, delivered.

Yeah, it seems worth the price if it happens even once, plus they have MOVs in there to neutralize some of the nasty spikes which are always coming from the lousy power networks today.

Nice. P.S: What does the temperature (F) of paper burning have to do with a fridge?

Yeah, that can be critical with refrigeration.

Yes, but all LA batteries show a volt or two drop even with small loads, especially after charging. Knowing how your specific battery is normally acting makes for happier times.

Sheeeeeeit! The Yeeco just came in. Neither you nor Amazon mentioned that this thing is the size of my thumb, not a business card like the rest of them. I saw the pics side by side on Amazon and they were all the same size, which is And the LCD is =maybe= 8pt type. I hadn't noticed that the entire meter was only 50x26x21mm with a display 1/3 of that. Drat. Bifocal Mode=ON. I'm going to request that Amazon and/or Yeeco adds that size info in the bullet points of that listing. It was a real shock, even though that info was right there, about the fourteenth line of type in the secondary description block.

Reply to
Larry Jaques

Give me the Luxuries of life. I can live without the necessities.

Reply to
Larry Jaques

You equate UPS with VFD? I guess that's what threw me. Yes, you can turn some generators into motors, too, but they're not as efficient, etc. But I think of UPSes as battery chargers which turn into AC power sources via those batteries when the AC fails, and don't see the reciprocity you do, I guess.

Most posters on that thread seemed to steer him into a brushless DC motor. That's what my eBike uses. 800w 3-phase DC controller and BDCM.

Yup.

Reply to
Larry Jaques

Basically the same thing as a 3 phase VFD. The "brushless DC motor" you have on your bike is "basically" a 3 phase motor.

Reply to
Clare Snyder

Converting DC to sinusoidal AC is the only difficult function of a UPS. I just assembled a DC UPS from a 12V battery, power supply, solar controller and a single diode. I tested it on a partly cloudy day and could see the power supply's AC input wattage drop as solar current increased. With enough sun the power supply's KAW reading fell to

0.0W. In the evening the PS assumed the full load, and when I unplugged it to simulate an outage the freezer ran off the fully charged battery.

The Alpi uses one that draws a constant 30W as the DC input voltage rises or falls. I learned how brushless DC motors work at Segway, and the math at Mitre.

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-jsw

Reply to
Jim Wilkins

So, initially, it's working as planned? Great.

30w and it works about 8x better than a 40w Peltier block. Nice.
Reply to
Larry Jaques

The remaining question is how it handles the return of grid AC when the battery is nearly discharged. The maximum charging current depends on circuit resistance and the battery's internal impedance when deeply discharged, which I don't want to test any more than necessary. The solution will have to wait until after my taxes are done.

The storm that hit Ed passed south of here. We are nearing the end of ice storm power outage danger so I can put this project on hold until hurricane season. The Alpi more than doubles the battery run time before needing a solar or generator recharge.

I've been using a Peltier cooler for grocery shopping. It's no answer for power outages because it draws down a battery faster than the fridge plus APC1400. The Alpi keeps ice cream at around 5F where it's scoopable.

I need to find the safe temperature setting to store frozen food a maximum of two weeks. 0F is for "indefinitely" long storage.

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-jsw

Reply to
Jim Wilkins

I'm very nearsighted. Sorry bout that.

The Yeeco meter I received tracks my 5-1/2 digit Fluke 8800 within

15mV from 3V to 28V. The error is -5mV at 3.0V, -10 to -15mV from 10V to 20V, and 0mV at 28V.

It matches my Fluke 8600 to 4mA at 1A and 2mA at 2A, after correcting for its internal consumption of 6.1 to 6.5mA. I can't measure as accurately above 2A but it appears to be within 1% up to 15A. I ordered a second one since the 90V 20A charge/discharge meter I received seems faulty, so I'll measure the Amp-hours into and out of the battery separately and compare totals.

I've been stocking up on meters etc in anticipation of a trade dispute with China. Hopefully I have enough now.

-jsw

Reply to
Jim Wilkins

I'm familiar with that concept.

Nice. Gee, you guys have all the weather. Me? I love the Left Coast, thanks.

I like zero. 30F might do it for short periods, though, but why risk it? 32F slows the deterioration to a minimum, zero almost stops it. I've had vacuum sealed burger and steaks in the 0-5F freezer for several years and they were fine after thawing. Ditto meat frozen with water surrounding it to prevent freezer burn. Send an email to Alpicool and see if they can translate it into what you're looking for. G'luck.

Reply to
Larry Jaques

That explains your not noticing the physical size difference. ;)

Not shabby at all.

Yeah, I hear that. Wish I could afford 6kW more solar panels, controller, and inverter right now.

Reply to
Larry Jaques

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