backup plan for grid outages

papab · April 2018

I'm evaluating options for grid outages of over a day. I don't thing we've had one that long for a long time, but as an old boy scout 'be prepared'. I have a 4.4W PV grid tied system in sunny colorado. With my 2000W SMA sunny boy secure power supply and a 2000W (4kw peak) inverter in my camper van I can keep the food from spoiling. Our well insulated sun tempered house will never freeze and probably be reasonably comfortable on a sunny winter day. If I add a 120/240 transformer I should even have enough energy to run the heat pump water heater. The weakness is the sewer (grinder) pump. Instead of a gravity sewer system the developer cheaped out and had everyone put in their own grinder pump.

Its a 1 HP 240V capacitor start single phase motor. I've measured inrush current at 26 amps @ 250V, running current at 6 amps. It would only need to run about a couple of minutes every day so energy isn't the issue, but inrush current is. I haven't received any help from the manufacturer (Eone), they suggest a 6.5 kw generator. I'd like to avoid that since I don't need it for anything else. If the xantrex really can put out 4000W surge I should be able to get at least 15 amps at 240V from a transformer. I have 250ah of AGM batteries and a 150 amps alternator in the van so I think I'll have enough on the 12V side. It looks like an inrush current limiter such as one of these:
https://www.ametherm.com/blog/inrush-current/ac-motor-inrush/
might work. I assume that if the inrush is limited too much the motor won't start. Any ideas if this would work?

mike95490 · April 2018

What is the Xantrex that you need 4Kw out of ? has to be at least 24VDC to handle a huge surge

4Kw @ 24V = 170A from the batteries and cables half that on a 48V battery. Too much voltage drop and you

have an inverter shutting down from under voltage.

I think a 6.5Kw generator is small, but you can try it. What's the septic sump capacity ? Or can you use a smaller grinder pump and run it longer ?

papab · April 2018

The only thing I need 4kw from the xantrex is for the inrush current on the pump. I have 1/0 cables. The grinder pump tank is 60 or 70 gal. This model is the smallest one they make & any other brand wouldn't just drop in. 6.5kw generator is what they recommended, so I don't think it's too small, but that's not what I'm trying to do. I'm trying to leverage what I have to get a capable backup. If I can't I'll just be like the rest of my neighbors and we'll be scrambling to find a generator to share, or bringing in porta-potties

mike95490 · April 2018

What is the model # of the xantrex ?

1/O cable is only good for about 150A so I hope you are trying this on a 48V system with very short DC cables, otherwise the DC resistance is going to shut the inverter down before it can deliver the starting surge.

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

My 1/2 hp well pump motor consumes 1,000w when running, and much more when starting. The chart below is for
capacitor start well pumps, with Franklin motors. ( 3 wire has the starting cap above ground in the control box, not in the well)

Looking at 230V 1hp I'd guess 2300watts running, 8510w to start, sturdy inverters should be able to deliver a 2x surge for starting for 2 seconds - look up the specs for your 4Kw inverter.

Image: https://us.v-cdn.net/6024911/uploads/editor/35/m86yayuzayv3.jpg

oil pan 4 · July 2018

You could probably find a 24v sewage pump.
Or really small 120v unit.

cow_rancher · July 2018

I'm sure the marine people use something that is battery powered...

Rancher

bill von novak · July 2018

papab said:

I'm evaluating options for grid outages of over a day. I don't thing we've had one that long for a long time, but as an old boy scout 'be prepared'. I have a 4.4W PV grid tied system in sunny colorado. With my 2000W SMA sunny boy secure power supply and a 2000W (4kw peak) inverter in my camper van I can keep the food from spoiling. Our well insulated sun tempered house will never freeze and probably be reasonably comfortable on a sunny winter day. If I add a 120/240 transformer I should even have enough energy to run the heat pump water heater. The weakness is the sewer (grinder) pump. Instead of a gravity sewer system the developer cheaped out and had everyone put in their own grinder pump.

Its a 1 HP 240V capacitor start single phase motor. I've measured inrush current at 26 amps @ 250V, running current at 6 amps. It would only need to run about a couple of minutes every day so energy isn't the issue, but inrush current is. I haven't received any help from the manufacturer (Eone), they suggest a 6.5 kw generator. I'd like to avoid that since I don't need it for anything else. If the xantrex really can put out 4000W surge I should be able to get at least 15 amps at 240V from a transformer. I have 250ah of AGM batteries and a 150 amps alternator in the van so I think I'll have enough on the 12V side. It looks like an inrush current limiter such as one of these:
https://www.ametherm.com/blog/inrush-current/ac-motor-inrush/
might work. I assume that if the inrush is limited too much the motor won't start. Any ideas if this would work?

You are going to have a hard time getting a 12V 2000W inverter (assume it's 12V since "camper van") to run high surge 240V loads. It would make a lot more sense to get a 240V 24/48V inverter to power that load.

Or just get am appropriate generator.

backup plan for grid outages

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