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Old 02-12-10, 12:45 AM   #11
Xringer
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I remember going up on the roof to bleed any air out of my old system,
and WOW the plumbing up there was at least 200 deg F.

~~

When I was looking at those 60 volt panels, I was thinking of just using 4 of them
into resistance heaters for my hot water. (Since they are the lowest W/$ PV available).

And, I'm still interesting in the idea. So, I'm trying to get a tracking mount set up
that can carry at least 4 standard sized panels.

So, what inverters are you looking at so far?

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Old 02-12-10, 10:58 AM   #12
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I already have a 48V UPS system, which I got from a computer salvage friend.

A UPS combines a charger, batteries, inverter, and automatic switch, all in one unit.

If I was able to supply 120V AC to the UPS when the sun is shining, it would take care of charging the batteries, and automatically make AC from the batteries when it was no longer getting power.

Grid-tie inverters are designed to directly handle high-voltage panels (with inputs up to 500 or 600 volts!) but are costly. The most basic high voltage one I have found so far is a SunnyBoy SB700, which is just over $1000. Even then, that one has a "safety-feature" of turning off when it senses that it isn't connected to the grid. So, running AC to my UPS might not make sense/be cost effective.

If I try to charge batteries directly, I need a solar charge controller. However, most of them are designed for 12, 24, or 48v. A single panel of mine makes MORE than 48V!
Some charge controllers feature MPPT - which can lower the voltage of a panel by converting some of it to amperage, which is really what the batteries care about anyways. Of course, this is fancy technology, which costs money. The Outback Flexmax features MPPT, can can handle a max incoming voltage of 150v. That means I would need to put all the panels in parallel, because even two panels in series could potentially add up to more than 150v. This would mean more wiring, a big combiner box, etc, etc. One of those charge controllers runs about $600.

If I did get a MPPT charge controller - that would charge the batteries directly. I would use the UPS as the inverter, and my garage could go off-grid - yeah!
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Old 02-12-10, 12:32 PM   #13
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Default This might sound crazy, but

I've been wondering what would happen if you tied the DC input of two regular inverters in series?

http://ecorenovator.org/forum/solar-...-inverter.html


Just stack two 28V (max) inverters to get a 56V input? Put 3 or 4 of your 60W panels in parallel to feed them??

They might balance out, since all the AC outputs would be tied in parallel to the garage gird.?.
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Old 02-13-10, 12:49 PM   #14
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After doing a little research, it looks like the big thing that I have to watch for is Voc - Volts Open Circuit - how many volts the panel can make in full sun on a cold day.

For my panels, it can be quite high. I already measured 97 volts in full sun in 15 degree F weather.

The trouble is that MOST of the more simple solar charge controllers for 48V battery packs CAN'T handle that high of a voltage.

The MPPT Chargers CAN handle that - usually up to 150V.
There are a few NON-MPPT that can also handle a higher Voc from the panels.
The Xantrex C40 can handle up to 125 Voc, which would be enough for single panels run in parallel.

It is my understanding that plain charge controllers basically "throw-away" any extra voltage that you have. So, that extra "headroom" of voltage I have with the 67V panels isn't going anywhere. The panels would put out 67V at one amp, but only something like 58V at one amp would be going to charge the batteries.

A MPPT charger would take advantage of that extra voltage to convert to a lower voltage but at higher amperage - thus a higher amp charger for the same amount of PV panels and sun! Yea!

The only products I have seen so far that handle really high voltage (5 or 600V) are grid tie inverters. I would LOVE to just plug one panel to the next to the next in series. It would make the wiring SO much easier.

But I don't want an inverter really - I just want a way to charge batteries. So, it looks like I need to run each panel individually to a combiner box, and then THAT into a solar charge controller.

You know what would be really cool? A 600V to 48V DC to DC converter. That would solve all my problems. Any got one of those kicking around?

Another thing that I did notice about the MPPT chargers is, although they are more expensive, they usually have some sort of built-in monitoring, and aux 12V (to activate a fan, alarm, etc.) and some other built-in features.

The less-expensive NON-MPPT chargers tend to be very basic, adding a display, etc, is optional and costs extra.
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Old 02-13-10, 04:15 PM   #15
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Default DC to DC

Maybe find out if someone can build one for you??

DC/DC Converter, retail, wholesale, off-the-shelf and custom, 5 watts to 800 watts


Edit:
When I was looking at those 60W panels, the BZ -HV units seemed to be in my price range.
I think both the 250 & 500W MPPT -HV chargers chargers will handle 100 Vdc (I think).

MPPT Charge Controls

Last edited by Xringer; 02-13-10 at 05:47 PM..
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Old 02-15-10, 01:27 PM   #16
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It looks like I got the UPS working!

I wired up 4 mis-matched batteries, which were only about half-charged, in series for 48V and ran them to the unit.

It looks like I can turn the machine on or off manually, whether it has AC connected to it or not.

Checking with my Kill-a-Watt, and a 60 watt lightbulb as a test load, the AC output from the inverter measured almost dead on at 60 hz (59.9)
Output voltage from the inverter was right about 117V AC.

I still don't have anyway of knowing for sure what the shape of the waveform it puts out is. I have heard terrible things about non-true waveform inverters and electronics like modern battery chargers. A friend of mine has an oscilioscope. Is that what is needed to check out the waveform of the inverted AC?

I would like to use the solar panels and a solar charge controller to recharge the 48V battery pack, and then use the UPS as an inverter to make AC from those same batteries. I imagine leaving the UPS OFF except when I need it for making AC.

The charging circuit in the UPS and the solar charger shouldn't interfere with each other, should they? I would think that both decide how much to charge based on the voltage of the battery. If the sun is shining, the solar charge controller would charge the batteries. If I flipped on the UPS then, it shouldn't charge the batts, because the solar charger would be raising the voltage.

On the other hand, if I was using the batteries a lot, and found that I was dropping the voltage on the whole pack, enough to want to recharge, and it is winter and cloudy for weeks, so the solar charging isn't doing anything, all I would have to do is plug in the UPS (to the existing grid-tie wall AC), and it would recharge the battery pack.

What I want to do is be able to take my garage "off-grid". Solar panels on the roof supply the 48V battery pack with power through the solar charge controller. AC power is supplied from the battery pack, as needed, through the AC outlets of the UPS.

Ideally, I would like to be able to charge the electric motorcycle, Citicar, or Metro through this system. I know the limit there is going to be how many amps those chargers take on initial draw. The battery charger I have been using has an analog pot adjustment, which can let you lower the amperage. If I just set this to less than what the UPS can supply, I think that will work fine.
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Old 02-15-10, 01:55 PM   #17
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An oscilioscope should show you the sine wave. I too have read that electronics can be quite finicky with cheapo inverters. Homepower magazine had a good article on this. I'm not sure how old it was though.
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Old 02-15-10, 04:20 PM   #18
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A UPS that's designed for use with computers, normally has a pretty clean sine wave.

If you do use an O-scope, remember to put the probe ground clip on the (round) ground of the outlet.
I've had a few students try to look at AC outlets and accidentally stick the probe ground clip on the hot side of the line.
It smokes the probe..

Be sure the scope/probe combo is rated for 120 AC-RMS Some scopes won't handle very much voltage and need a probe (w/ voltage divider) to get up to higher voltages.
120VAC has some pretty high Peak-to-Peak voltage..
Brushing up on ac circuit fundamentals


Jeepers, that modified sine wave sure looks like a square wave to me!!

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Old 02-15-10, 06:31 PM   #19
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Here's some video for you guys to get a better feeling for what I am doing.





Still a third video coming - it's uploaded to YouTube but not processed yet.

So far, it looks like I should be able to hook the UPS to the batteries, but just not plug the inverter in to wall power. That way it doesn't ever try charging the batteries at all, it only acts as an inverter.

I am guessing the sine wave from it will be fine, but I would still like to check it.

The next big thing is to decide on what solar charge controller I want. I need one that handles 48V battery packs, and has at LEAST a 100Voc input. MPPT would be nice, as the panels can put out fairly high voltage.
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Old 02-15-10, 07:58 PM   #20
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That UPS looks very much like the one I have at work under my PC desk..
I forget how many batteries it has inside, I changed them once after
I pulled the unit out of the salvage room..



Did you look at these chargers?? MPPT Charge Controls

The 500W are $200 and the 250W units are around $120 on Ebay these days.

They also make an HV (High Voltage) version of these which are good to 100VDC (or so I've heard)..


Cheers,
Rich

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