HV DC fuses

mike95490

I'm looking for some HV DC fuses, at low amperage. I'm going to get a 375V DC- 32V DC-DC converter, and want to hook it to my PV array, but need a fuse, just for the heck of it.
I only need 2A, but it's got to take 400V DC, which means there will be a good plasma arc if it trys to blow.
Suggestions ?

Vicor DC-DC module:
http://www.vicorpower.com/documents/datasheets/ds_375vin-maxi-family.pdf

From 32V, I can charge batteries or whatever, in an emergency.

niel

Re: HV DC fuses

you may have to send for them. a simple search turned up some. here's one of them: http://www.hilltech.com/products/power_components/Fuses.html

Windsun

Re: HV DC fuses

Standard KLK or KLKD fuses, like these http://store.solar-electric.com/pspv.html but we don't usually stock anything under 5-6 amps.

Solar Guppy

Re: HV DC fuses

mike90045 wrote: »

I'm looking for some HV DC fuses, at low amperage. I'm going to get a 375V DC- 32V DC-DC converter, and want to hook it to my PV array, but need a fuse, just for the heck of it.
I only need 2A, but it's got to take 400V DC, which means there will be a good plasma arc if it trys to blow.
Suggestions ?

Vicor DC-DC module:
http://www.vicorpower.com/documents/datasheets/ds_375vin-maxi-family.pdf

From 32V, I can charge batteries or whatever, in an emergency.

Since I think I know what your up to, it won't work ... DC to DC converters are designed with the source as basically a infinite supply. In your case if even for a millisecond, your load on the output of the converter is more than the source ( solar ) can handle, the unit will crash the array.

To do what you want the converter has to be programed ( smart dsp/cpu ) to deal with the solar V/I curve which inverts on the vmp point, in respect to what a typical pwm chip understands

mike95490

Re: HV DC fuses

Solar Guppy wrote: »

Since I think I know what your up to, it won't work ... DC to DC converters are designed with the source as basically a infinite supply. In your case if even for a millisecond, your load on the output of the converter is more than the source ( solar ) can handle, the unit will crash the array.

Hopefully, I'll never find out. However, the output of the dc-dc converter is way less than my array can supply. The converter has a VERY wide range of DC input, 250 - 425 V with it's 400W output at 32V - input, including losses, will be less than 2 amps, siphoned off a 11A array. The grid is down, and the GT-inverter is off, and the DC-DC has output current limit, so I'm not expecting troubles.
How can a moderate 2A load "crash" an array ? There's no "smarts" in PV panels, they get light, and then put out power. I understand you "could" short the outputs for a period (till the wires melt) but remove the short, and you have power.

BB.

Re: HV DC fuses

I think SG means that the converter is an active device with, essentially, a negative resistance. As the voltage falls, the current increases, further pulling the voltage down.

As an example the Solar Panel's output Vmp * Imp forms a peak in the power vs voltage (or vs current) curve. All it takes is for the DC converter to draw 0.001 Amp more than Imp (at a particular solar level), --the voltage will fall fairly dramatically, as the DC converter is a constant power device, the next cycle of the DC converter will draw more current, further pulling down the voltage--or quicly "crashing" the power output of the solar panel.

Depending on how the converter operates, and the output load characteristics, the load or the converter's DC input may need to be manually disconnected until the cloud or shadow passes by.

I too understand why you want to do this--sort of the same discussions we had with SG on his site (I think it was there) were we wanted some sort of battery charger/DC converter that we could connect to our solar panels when utility power has failed and our Grid Tied solar system (and its expensive panels) is otherwise useless.

Even a less than perfect solution would be better than nothing (say a 400 Vicor module connected to a 3+kW array).

Would the Vicor module work OK connected to the ~10x larger array--seems like it might (may have to add a few good high voltage capacitors to the converter's input)--may create some nasty high frequency oscillations (RF noise) on the converter's input without them (oscillations could interfere with the function of the Vicor module too)...

But, you could also just connect your 300 VDC nominal array with 10 amp output to a 32 VDC or 48 VDC battery bank directly and get ~320-480 watts (peak) of energy directly from the panels (just install a simple relay and voltage monitoring circuit to either disconnect the array when the batteries are charged, or to connect a diversion load).

-Bill

mike95490

Re: HV DC fuses

BB. wrote: »

But, you could also just connect your 300 VDC nominal array with 10 amp output to a 32 VDC or 48 VDC battery bank directly and get ~320-480 watts (peak) of energy directly from the panels (just install a simple relay and voltage monitoring circuit to either disconnect the array when the batteries are charged, or to connect a diversion load).
-Bill

I can connect the PV to the batteries early AM, while there is no power, but say noon comes along, batts are full, and then what, 300VDC @ 9 A is going to cream any relay I know of. Heck, even the GT's DC disconnect is an admittedly weak solution, if used at full power, they guess the life as less than 100 cycles, I read someplace. I was actually thinking of a FET to control the DC.
Placing a bank of caps at the inputs is a good idea, I'll keep you posted.

BB.

Re: HV DC fuses

Another method keep the voltage down (again--just speculating)--get a good sized diode that can manage 10+ amps. Connect the solar array through the diode to the battery. Connect a 10+ amp capable relay (or FET) between the solar panel and its return (before the diode/battery connection.

When charging, the array voltage cannot get more than about 15-16 volts DC. You can now open and close the shunt relay to limit charging by shorting the solar panel outputs.

For redundancy, you could connect several diodes in series and parallel... In series (with a ~15 amp fuse to the battery) to prevent a shorted diode from dumping battery current into the relay. Parallel diodes to prevent one diode failing open and causing high voltage from the solar panel causing your relay to arc on opening with 300+ volts.

-Bill

Solar Guppy

Re: HV DC fuses

Mike,

Just use a proper rated HV ( 600 VDC ) disconnect and it makes no difference on the voltage differential. The Square-D HU-321 is the standard, I actually have a couple laying around you can have one if you pay the shipping.

So, just have the array in one side, battery on the other and throw the switch when needed when the grid fails for you 100 watts of energy.

You also will get more bang for your buck if you move upto 48V, outback 3048's can be had for 1200 bucks and with 4 walmart deep cycles will be a useful backup system. Even with the switch without a charge controller, you good for 500 watts most of the day ..

Send me a PM on my site if you want the disconnect