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Author Topic: buggerit... psuedo solar doesn't work any suggestions?  (Read 4496 times)
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« Reply #15 on: November 03, 2009, 09:17:23 PM »

You could throttle it with a constant-current source (essentially an active electronic variable resistance), set to something just less than the solar controller can manage, and put that between the 48v bat and the solar controller.
Linear ones are fairly simple to design but at high currents can get quite hot so would need heat-sinking.
Switch-mode ones run cool but are more complicated to design and might mismatch with your solar controller which is essentially a big switch-mode device itself.

The simplest version of this is just a big power resistor sized to restrict the input current below the 58 amp limit (130% of 45 amps).
A few simple calculations show that the worst case voltage drop would be 24 volts and at 58 amps this would need a 0.413 ohm resistor.
Nearest standard value of 0.47 ohms would limit to 51 amps at 24 volts.
If used continuously it would then dissipate 1.2KW, but the chances are that the voltage drop is less than 24 volts and the Pulse Width Modulation of the solar controller will limit the time it is dissipating to a small % of that.
Try a 50 watt resistor if you can get one. And fit a 60 amp fuse.

When testing my solar inverter I simulated a solar source with a variable voltage, current-limited, bench power supply.
Soar PV is essentially a current-limited variable voltage power source.

The current-limiting bit is what seems to be missing in your setup.

Hope you haven't blown it up too bad.  whistlie

Good luck.

« Last Edit: November 03, 2009, 11:25:52 PM by davebodger » Logged

Soladin Grid-Tie 400Wp tracker in London NW5.
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« Reply #16 on: November 04, 2009, 02:07:40 AM »

could you use a DC to AS converter, then a transformer, then rectify the output back to DC

sounds like a hassle... but it's pretty simple really... should be cheap, able to be setup to take plenty of amps... and each of those things is very efficient ?

if you set it up right, so 48v in is 24v out (or whatever constant charge voltage you want) it would be completely self regulating

tho you'd have to the the EQ charges etc.. yourself ?
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« Reply #17 on: November 04, 2009, 09:41:07 AM »

On boats I have used the DC DC converters to charge a 12v from a 24v battery. I only used the 3A Alfatronix unit.(any size should work) All I do is put a small wirewound resister in the output to limit the max current. As the batteries reach full charge the resistor has less effect as the current drops. The battery voltage then comes up to the correct unit output voltage.

1.98kWp PV (11 x Sharp 180 and SB 2.5)
20 x 65mm Thermal and 180ltr unvented
Powervault 4Kw - G200 Lithium-Ion (LiFePO4)
9000ltr rainwater storage   Plymouth
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« Reply #18 on: November 05, 2009, 01:04:44 AM »

Well you best tell Outback then that the product they are selling does not work & that they should stop advising that the amps out will be caped at the max level (the input amps are much lower due to high input voltages). They do say that to high a V will blow it. They tell you that extra amps available from the array will not damage the unit.

I have a 1200w array. That could be 100amps if I let my bat get to 12v. The output amps are caped at 80amps. I have seen the full 80amps out on sunny days & have no doubt that its capping it at that 80amps (shortly before it was a 800w array & that often did the full 800watts & slightly more). I dont think its burning that extra power as it does not give off that much heat. I assume it manipulates the MPPT to bring the input amps & v to levels that reduce the outputs to the capped levels.

100A into a 80A rated controller is only a 25% overload so you'll get away with it.  The throttling (of any kind, current or voltage) on these PWM controllers is by high frequency switching on and off.  If you switch a 48V, 100A source on and off at 10kHz with a 50% duty cycle into a 24V battery, the average current delivered looks like 50A but the FET switches are having to withstand 100A pulses.  If you connect up a 48V battery as the source it can easily deliver its CCA current rating (for engine starting) of maybe 1,000A.  The FETs will go pop.

3.58kWp & 800Ah LiFeYPO4 off-grid(ish). See 'Cobbled together PV in W.Sussex' (in "Show Us Yours")
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« Reply #19 on: November 05, 2009, 09:25:57 AM »

I guess in my case the controller is only handling a few amps on the input as the V is around 100vdc.

Navitron solar thermal system
30 x 58mm panel 259L TS
1200watts solar 120vdc
FX80 Solar controller
2 x Victron Multiplus II 48/5000/70
Cerbo GX & GX 50 touch
BMV 700
6kva genny
48v 1000ah
Grid Possibly coming soon
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