AC or DC?

[DirtMerchant]

 I have another posting on this forum detailing my ST 7.5 woes...now it has me wondering....My project is off grid and currently I have solar and some scrubber batteries along with a Prosine 2000watt inverter. I also have but do not have connected, a 3000 sine wave inverter (chinese).

I have built up a Powerline 6/1 with an ST 7.5 head, it has the usual light flicker and growls, does not appear very well built and power from it is probably not very clean. Now I am starting to wonder if going with a DC generator to recharge the batteries and just use the inverters for power is a smarter move. Weighing the pros and cons, it would seem DC to the batteries and using the inverters would be much smoother and cleaner power versus the ST that is dirty power with flickering that can't be good for any motor or appliance.

So then the question becomes where to find a DC alternator that can tolerate continuous duty at high amperage ? I am thinking up around 300amps ?


 

[BruceM]

The ST's power can be cleaned up by and AVR off of the mains plus metal film 0.1 uF caps x 4 on the bridge, perhaps 40uF of motor run cap on the output if needed to clean up the ST "ratcheting".   Balancing transformer for 120V loads has also been covered here to eliminate growling, which can be eliminated in other ways, also.  You paid peanuts for the ST relative to better quality heads, so you must expect to do some work.  It's a good value DIY generator head with some well known issues to address (including replacing the bearings and doghouse).  I'd rather have a Marathon head if only someone else would pay for it. 

Starting surge current for single phase induction motors are often 4 times the run current, as high as 8 times, sometimes.  That takes a hell of an inverter for a 3/4+ hp motor, and it's why inverters alone aren't always used.  Many budget conscious off grid homesteads use the generator for occasional big motor use and for shop tool power instead of trying to handle that load on inverter and batteries.  My Listeroid does both air compressor and AC duty, and on laundry day fills the gravity feed storage tank plus while running the washing machine.  This plus a propane refrigerator/freezer let's me have a much smaller battery and PV system. 

Just something to think about.






 

[DirtMerchant]

 I don't believe I have anything short of the air compressor that is greater than 0.5 HP, the well pump is a 1/2 hp 120vac and have even run my mig welder from the inverter without issue. I am considering jumping up to a 24v system with a 5000 watt inverter though just to have more overhead.

The off grid location is just a weekend place, solar recharges the batteries during the week from the drainage over the weekend, so far it has worked really well, but next winter would really define if I could get by with what I currently have.

[honda lee]

What are scrubber batteries?

[mike90045]

Your loads (appliances, light fixtures) will drive the decision, along with the size of your house.  For a very small cabin, you can use 10 ga wire to distribute 12VDC to the appliances you have.  A small (Morningstar SureSine 300) inverter can power the electronics that need AC power.

But to scale things up to a cabin larger than 400sf, wire run lengths/gauge become prohibitive, you have more appliances that you can't get in DC versions.

Charging, will you have solar or hydro, or only the generator ?  What's more reliable, and is capable of charging the batteries properly.  Can it supply enough amps to de-stratify the batteries?  What's the backup when something dies?
 Does a DC alternator controller have enough setpoints for 2 or 3 stage charging ?  Can it shut off the genset when batteries are full ?  

I like the http://www.microcogen.info/index.php?topic=50.0  page with a listeroid and an Axial Flux alternator paired with a MPPT Charge Controller.

[mike90045]

What are scrubber batteries? 

Small deep cycle batteries used in industrial floor scrubber/washer machines for grocery stores and warehouses

[BruceM]

Given your small motor loads, you might be a good candidate for all inverter operation.  It certainly fits your weekend only use well.

[Horsepoor]

BruceM's comments are spot on. I cleaned up my ST's wave form and raised the output voltage for just a few dollars. Please review photographs in post # 62 http://www.microcogen.info/index.php?topic=1833.60

More good news, the capacitors are on sale for 49 cents each at: http://www.mpja.com/1000uF-100VDC-Filter-Cap/productinfo/18070%20CR/

Bruce