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Old 02-15-10, 11:01 PM   #21
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I took a look at the BZ solar charge controllers. They seem to be the cheapest with MPPT on them.

The high-voltage version is listed as 100Voc max input. I wonder how specific that is. I was hitting 97Voc on a 15 degree F. day. I bet my panels could break 100Voc when it's colder.

I noticed that the Xantrex and Outback MPPT chargers list 150Voc as the max input. Even though those controllers are more expensive, they do have some nice features, including remote monitoring, aux out, and built in displays listing amperage, voltage, etc.

Any of the cheaper chargers will really still need some ammeters, volt meters, etc added to the system. Lots of those things can be salvaged or had cheap, but since this is for a detached garage, being able to read all those things from inside the house sounds appealing.

There is still the possibility of some sort of DC/DC conversion to allow me to use all the panels in series, and then convert the high voltage DC to low voltage DC, and run it through a less expensive charge controller.

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Old 02-16-10, 06:36 AM   #22
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IIRC, those panels will have higher than normal output for the first few weeks..

I guess you could design and build some 48V MPPT boxes, but do you really
NEED maximum performance out of your panels?? Or, will they do the job with less
costly hardware?
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Old 02-16-10, 04:26 PM   #23
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If I am going to mess around with solar, I should actually learn about some of this stuff.

A while back, I joined the MREA and signed up for the entry-level solar hot water class. Being a member gives you a discount on the classes.

I took a look at the on-line listing of available classes. Turns out there is a PV-101 class being held about a 40 minute drive away, two days from now.

I signed up for it.

Also, I have seen that the Xantrax C-40 is a pretty reasonably priced PCM charge controller. It will handle 12,24, or 48V battery packs, and has a Voc input of up to 125V. For $125, I could buy one (no display or anything on it) add my own analog ammeter, voltmeter, etc. and be ready to go.

If I later wanted to invest in a fancy MPPT charge controller, the C-40 could then be used to charge a 12v pack with some of the other small PV panels I have kicking around. I could even mount it in my camper!
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Old 02-16-10, 09:46 PM   #24
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That Xantrex CM LCD Digital Display looks petty nice, but at $74 ??

I read up on the C-40 weeks ago and was impressed at what it could do.
Just for charging lead-acid batteries, it should do the trick..
IIRC it's a standard 3 stage unit.

If you want the BZ (MPPT) unit, but are worried about the 100V limit,
you should investigate your panels some more. Will they ever go over 100V when in parallel? It shouldn't be to hard to find out for sure.
I know they are in use down in Australia (on homes).

Heck, the BZ HV units may have been designed for your panels..
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Old 02-19-10, 09:08 AM   #25
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Old 02-19-10, 07:34 PM   #26
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How did the class go? Did you learn much good stuff?

Cheers,
Rich
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Old 02-19-10, 09:17 PM   #27
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Yeah, it was just the basics class, but it still covered a fair amount. Lots of fun.

We got to go outside and use a Solar Pathfinder. That was kinda cool!
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Old 02-22-10, 11:43 AM   #28
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Yesterday, I was over at my friend, Tom's house, and got to use his oscilloscope to test out my 48V UPS.

Here's a bit of video of us playing around with it.


It turns out that the inverter of the UPS IS TRUE SINE WAVE, (which I thought/hoped it would be) but it actually gave better AC power than what came from Tom's wall outlet!

The UPS only converts power from the 48V battery pack to AC when it senses a disconnect from the wall power. We did that by flicking the switch on the power strip. The waveform stayed very nice - no "glitch" or anything - just a seamless transition from wall power to battery power and back.

In my case, I am not really planning on using this device as a stand-alone UPS (although I do have some clever ideas for that as well...) Rather, I just want to use the inverter section of the UPS to convert power from a 48V battery pack to 120V AC.

Charging of that battery pack will be done from the solar panels through a (still undecided upon) solar charge controller.

Using the 48V UPS saves me the cost of a solar true-sinewave inverter, which can be VERY expensive. On the downside, the UPS is only designed to run 2200 VA peak, although it does have several power outlets on the back, including two 20 amp outlets.

I would also like to add an extra output to the solar charge controller, as both my motorcycle and CitiCar use 48V battery packs. Rather than charge a 48V battery pack, invert it to AC, run that to a 48V charger in the vehicle, which converts it back to DC - I could more or less run the PV panels straight to the EVs' main battery pack.

The motorcycle doesn't even have an aux 12v battery, just a DC/DC converter. The Citicar would still need a 12V charger hooked up for it's aux battery, although that could be swapped out for a DC converter as well.

For my electric Geo Metro, it would require use of the UPS/inverter because it runs typically at 96 or 108V. I would simply plug the car (with its built-in charger) straight into the UPS. In case the UPS power pack starts to run low on juice, it SHOULD automatically turn off AC to its outlets. I would want to double-check that with some real world-testing though.

Anyways, I am very excited that it looks like the UPS should work great for what I want it for. I still may add an extra fan or heat sink in it if cooling during longer run times is an issue.
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Old 02-22-10, 02:42 PM   #29
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Good looking wave-form! That's what I expected you would see. After looking
at the modified wave form, I was mortified.. No way I would want that feeling into my PC!

How much power does the electric Geo Metro need for a medium speed charge?
It seems like a full house EV car is going to be an Amp hog.. And mostly feed at night..
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Old 02-22-10, 03:16 PM   #30
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The Electro-Metro would definately be the energy hog.

It uses a charger which is adjustable for 72 to 108V battery packs, and can pull up to around 1800 watts from the wall, but typically, we don't like to do that.

For the last while, I had been running the Metro at either 96 or 108 volts. Lets set the car up as 96V, because the math is so easy.

Also, we'll turn down the amperage on the charger, with 5 amps, used as an example.

At a 5 amp rate of charge on a 96V system, that is 480 watts. The PV panels I have are rated at 60 watts, and I have 8 of them.
60w x 8 = 480 watts!

Not bad, the car and the solar system are PERFECTLY MATCHED! Of course that doesn't account AT ALL for the built-in inefficiencies of inverting from 48V DC to 120vAC and the charger converting to 96+V DC again.

Also, my batteries are 95 amp-hours. (lets round to 100 to make it easy.)
If my batteries are half run down - we need to replace 50 AH of energy to fill them back up. If we are charging at 5 amps, that's ten hours of charge time.

That might be possible in the height of summer. Around the solstice I might be able to get that much. Otherwise, Its more likely that I would have to let the car sit for MORE than one solar day to get that much energy.

On the other hand, if I just have to run a couple of errands, I may only run the battery pack down just a little bit. Perhaps little enough that only 5 or six hours of solar charging would be needed.

Also, since the solar panels are routed to stationary batteries, and THOSE are hooked up to the inverter, I COULD charge an EV at night, but I would want to make sure my PV system batteries outweigh my EV batteries, and have a low-voltage cut-off to deactivate the inverter if the system batteries drain too low.

Alternatively, my electric motorcycle uses 4 55AH AGM batteries. If those are run half-down, that's only 27.5AH to replace. If the cycle is hooked directly to the solar charging system (instead of through an inverter and AC to DC battery charger) it would be much more efficient.
The PV panels basically make 1 amp each. So 27.5AH/8 amps is just under 3 and a half. The PV would recharge the cycle pretty quick - only half a day.

The Citicar (with a 48V battery pack) would be similar in charging, except that is would have a battery pack double the capacity of the motorcycle. Still only 8 hours of sunshine for a complete charge.
Again, these are all round numbers and battery voltage changes as the batteries charge, etc. so some of this will just have to be tried out in the real world, once I get all this going!

I imagine I would charge EVs from the solar system when I would be at home during the day. At night, (off-peak!) or if I need to turn up the charger (for whatever reason) I could just plug EVs straight into my wall grid-power as I have been doing so far.

PS: I just ordered a Xantrex C-40. It's only $140, has a warranty, and could be repurposed in the future, should I decide to upgrade to a MPPT charger or other system. This is just the basic version - no fancy display or remote reading - but I can upgrade to that in the future if I wanted to.

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Last edited by bennelson; 02-22-10 at 03:20 PM.. Reason: typo
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