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Ninjarider2003

Allan.

Factor 1. For simple cost of installation. Higher voltages low current can transmit through thinner wire. Low voltage high current needs a thicker wire. Im going to start of with 1 panel and work my way up as i go. During early spring we buy poultry that requires heart lamps 24/7. I have estimated that i may need up to 16 panels during my peak usage months. I could do 18 volts at 80 amps, Or i could do 80 volts at 20 amps. For maximum light saturation installed on pole with a sun tracking system i could be looking at 40- 50 ft of wiring. 80 amps to travel 50 ft with a 3%volt loss requires 3/0 wiring while 20 amps traveling the same distance would need 4 gauge. Now the aluminium 4/0/3 wrote at the hardware store might come out cheaper than using 4 gauge and will also play a factor.

Factor 2. At 18 volts i have to wait longer in the day to achieve a voltage capable of charging. At 80 volts i can acheive a charging voltage just after sun up.

Now i have played with the idea of getting a rotary tumbler switch made turned by a stepper motor to change the panels back and forth from 4 series to 4 parallel.

MarkT i will look into that chip. Got a stashed on it pulled up already.

allanhurst

#16
Oct 31, 2016, 05:57 pm Last Edit: Oct 31, 2016, 06:16 pm by allanhurst
OK - have your panels in series....

But now you still have a problem with the ?-80v input, 14v ?amp convertor - as I mentioned earlier, such devices aren't trivial - it might be cheaper to buy thicker wire by the time you've blown up a few prototypes and maybe yourself.....

2.5^mm solid copper as used in the UK for house wiring is reckoned ok to 22A.

The output voltage of a solar panel rises fairly quickly with illumination - it's the internal resistance which drops as the light gets brighter, so you may not gain that much.

Do you want something that works,  or months of frustration and magic smoke trying to get something a bit better..?  How many high power switchmode psu's have you designed?
There's a lot more to it than just driving the switches.....


regards

Allan.

MarkT

I'd say series everytime, much less copper needed.   You know aluminium wire is approx 3 times poorer
at conducting than copper (size for size) don't you?

Remember that wiring in series requires reverse diodes across every panel to prevent back-driving
when a panel is in shade.  Depending on what type of panel these may already be fitted.  You also
need a diode in series with the whole array to prevent current flowing the wrong way when dark. Again
some panels may already one per panel already to make wiring up simpler.

If your charge controller can handle MPPT from a wide range of input voltages then all in series is a
good approach (though you might want to limit the highest voltage in the system for safety reasons)
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

allanhurst

Hi MarkT..

of course you're right  - perhaps you could provide  us all with a detailed debugged design and layout for a 5-90v in , 14v 40A+  output buck/boost  convertor .

Wouldn't mind such a gadget myself. Nice bit of kit.

regards

Allan

CrossRoads

Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

allanhurst

#20
Oct 31, 2016, 10:26 pm Last Edit: Oct 31, 2016, 10:31 pm by allanhurst
Those gadgets are designed to run from 85-265ac,  not <= 80v dc from a solar panel of unknown impedance....

regards

Allan.

Ninjarider2003

Quote
2.5^mm solid copper as used in the UK for house wiring is reckoned ok to 22A
2.5 mm diameter wire at 50 ft would have a 10% voltage loss when trying to transmit 20 amps. To keep high efficiency a 5.19 mm diameter wire at 50 ft would have a voltage loss of 3%.

MarkT I looked at that chip driver you suggested looks like its rated for 80 volts. It would bring down the cost of the build. And increase efficiency. Tried looking for other gate drivers and google doesnt want to cooperate. So i may stick with that one.

Only other question would be the inductor. Found a bunch of shielded inductors but i have not a clue yet as to what values to start at. Shielded would prevent interference on the board and components but would still have interference generated by large moving current.

But i will take your advice on using an oscilloscope.

allanhurst

#22
Nov 01, 2016, 12:00 am Last Edit: Nov 01, 2016, 12:04 am by allanhurst
The impedance of the solar panel will be much higher than the wiring .... but go ahead  - have fun.. and look for loads of magic smoke!

regards

Allan

Wawa

If it was me, I would wire the panels for 48volt.
Still resonably safe to work with when "live".
I would probably use an off the shelf MPPT charger (ebay), going to a 24volt deep-cycle bank.
More panels could be cheaper and easier than a tracking system.
Calculate the battery requirements for heat lamps.
You might be in for an unpleasant surprise.
Leo..

allanhurst

#24
Nov 01, 2016, 01:11 am Last Edit: Nov 01, 2016, 01:27 am by allanhurst
OP if you've no idea what the inductor should be you're in for a LOT of magic smoke!

Look at eg LT's website for loads of excellent guidance on designing switchmode psu's

regards

Allan

ps - and yes - I have designed big switchmode psu's professionally. - it isn't trivial.

Ninjarider2003

Most off shelf mppt charge controllers ive seen they want upwards of $200.00 to be able to manage a max of 4 panels. That means 4 charge controllers at $800.00 to be able to control 16 panels. Im sure if i only blow up 20 fets and manage to get it to work correctly while only loosing 20 fets that i still come ahead cheaper.

Ive looked at a few of the cheaper ones and they do not appear to be actual buck converters but pwm charge controllers. Id prefer the higher efficiency of a buck converter.

MarkT whats your thought of the ltc4444 for my application. The fet driver you mentioned is a full bridge. The ltc is a half bridge it says its a syncronous control but does not provide a wave form output graph to verify.

allanhurst

#26
Nov 01, 2016, 01:44 am Last Edit: Nov 01, 2016, 02:01 am by allanhurst
The professional devices are expensive because it isn't easy.

If (you can get away with a less efficient but cheap reliable and simple solution see my post #5.
I'll modify the values for panels in parallel if you like - that would be my preferred solution.
)

else (pay the money || sniff the magic smoke!);

regards

Allan

Wawa

#27
Nov 01, 2016, 02:21 am Last Edit: Nov 01, 2016, 02:23 am by Wawa
How big are your heat lamps. 250watt?
Are you planning to use batteries to bridge the night.
One lamp will drain a $250 deep-cycle battery in a few hours (can't drain them more than 50-60%).
Calculate about $1000 worth of batteries per heat lamp, just to get you through the night.
And they need replacing after three years.
Batteries alone might already be more expensive than the power bill you have now.
Do the maths.
Leo..

Ninjarider2003

This spring the wife was rocking 7 (250watt) heat lamps. After opening the power bill she said shell never do that again. Ive repeatedly told her a reptile ceramic heating element produces just as much heat but far less consumption and she wont use them. She has agreed to rock no more than the required 2 heat lamps. 1 has to stay in the pump house the other for poultry raising. Second heat lamp only really needs to run for about 1 month.

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