Arizona_Mike
Newly Enlightened
- Joined
- May 4, 2015
- Messages
- 117
I am looking into getting a large capacitor to help stabilize the battery voltage in my solar battery bank at my cabin when the microwave and/or AC comes on (the microwave seems to have a particularly low PF which the inverter hates). Actually microwave 2 (in 6 years of 3-5x annual trips) is almost dead from my old pseudo sine wave inverter but I just put in a true sine wave last weekend so future microwave #3 should be the last. I'm also looking to reduce ripple when manually equalizing from a full-wave rectifier charger ("buzz box" salvaged from an old 1970s GMC motorhome) adjusted by a Variac. I've had some sticker shock looking at large aluminum caps.
"Car Audio" Caps are the right size and voltage range and price and most of them have a digital voltage display built in (nice for my system and adjusting charge) and come with an initial charging/discharging resistor (or sometimes circuit), but I suspect like batteries, many of the capacity claims 1.5 Farad, 2 Fared, etc. are fraudulent.
I estimate an equalization current of 4.5-6.75A at 15.5v starting with a fully charged battery bank based on manufacture specs (with ripple currents as high as 20A when equalizing--less when charging from the buzz box (even less when bulk charging). I will not allow the buzz box to float charge and will only use it with the generator on low batteries. My generator puts about about 105-111v (more at higher load ironically--must be due to the throttle) and I get about 13.8v RMS at that input voltage. In should have no trouble hitting 15.5 RMS with my 110:0-130v Variac.
I calculate I will need 0.75-1.13 true F to keep ripple down to 0.05v (.38-.56 true F for 0.1v). I don't know the reactance of the rectifier but using the general 2-3x rule for ripple current, I will need about 20A ripple current rating (which seems to be a hard to find number for audio caps but on the low end of large AL cap ratings so I suspect I will be fine).
Does anyone have any experience with such Caps and know where I can find reviews and actual capacitance measurements? Brands to trust and brands not to trust for actual capacitance or quality issues?
Mike
PS. Anyone know of a low-wattage small/cheap microwave with a good PF?
"Car Audio" Caps are the right size and voltage range and price and most of them have a digital voltage display built in (nice for my system and adjusting charge) and come with an initial charging/discharging resistor (or sometimes circuit), but I suspect like batteries, many of the capacity claims 1.5 Farad, 2 Fared, etc. are fraudulent.
I estimate an equalization current of 4.5-6.75A at 15.5v starting with a fully charged battery bank based on manufacture specs (with ripple currents as high as 20A when equalizing--less when charging from the buzz box (even less when bulk charging). I will not allow the buzz box to float charge and will only use it with the generator on low batteries. My generator puts about about 105-111v (more at higher load ironically--must be due to the throttle) and I get about 13.8v RMS at that input voltage. In should have no trouble hitting 15.5 RMS with my 110:0-130v Variac.
I calculate I will need 0.75-1.13 true F to keep ripple down to 0.05v (.38-.56 true F for 0.1v). I don't know the reactance of the rectifier but using the general 2-3x rule for ripple current, I will need about 20A ripple current rating (which seems to be a hard to find number for audio caps but on the low end of large AL cap ratings so I suspect I will be fine).
Does anyone have any experience with such Caps and know where I can find reviews and actual capacitance measurements? Brands to trust and brands not to trust for actual capacitance or quality issues?
Mike
PS. Anyone know of a low-wattage small/cheap microwave with a good PF?
Last edited:
