Emergency backup for medical equipment system design

[oneandahalflegs]

Newbie here, but I am an engineer so.... ?

Anyway I have ALS and I require a vent , and therefore electricity, to breathe. I have been avoiding the emergency backup question for too long. Isaias was scary, 17 hours without power. I won't go into the BS I had my wife do to keep me alive. This event focused me. Solar with battery backup was the way to go..... then Covid killed the Aviation Industry and my employer laid off 45% of its work force. That included me.

Several months later one of my friends found out about my situation and started raising money for a temporary solution. The support was overwhelming.

So here I am planning a design that requires the least effort for my wife to handle. I jumped on the purchase of a battery, right or wrong, and bought the second generation 24V powerwall from bigbattery.com. 5kWh/203Ah. I also have a cheap small generator that I plan to use to recharge the battery and extend run time. I use Home Assistant to view, control and in some cases even automate things in the house. I want to do the same here so I need modbus. There is picture below that describes what I am trying to do.

So far I am looking at
Inverter charger: Victron Energy MultiPlus 24/3000/70-50 https://invertersrus.com/product/victron-energy-pmp243021102/
Inverter comm: Venus GX https://invertersrus.com/product/victron-venus-gx/
Battery monitor: ???

What else am I missing? comments, suggestions?

 

[John Frum]

Those inverter generators don't last long.
And the ethanol in the gas makes them a pita to maintain.
The carbs get gummed up.
Also storing gas is a problem.
Suggest you get a dual fuel one and run off of propane.
Also its probably best not to load more than ~66 percent.

 

[svetz]

...What else am I missing? comments, suggestions?

Start with a power analysis (see Energy Audit in the signature below) to make sure whatever you get will actually meet your needs. Plan it all out, then post your data and results for review.

If you have natural gas where you live it might be a better fuel source for the generator, no need to truck fuel (although in some disasters, e.g., earth quakes, they shut off the gas so make sure it'll work for your area).

 

[snoobler]

Inverter charger: Victron Energy MultiPlus 24/3000/70-50 https://invertersrus.com/product/victron-energy-pmp243021102/
Inverter comm: Venus GX https://invertersrus.com/product/victron-venus-gx/
Battery monitor: BMV-702 (712 if you want bluetooth, but the GX makes it unnecessary)
Charge controller: Victron SmartSolar 100/50
Solar Panels: 1200W

Added a couple items and concur with svetz's energy audit if you haven't already done one. A big fridge alone takes 2kWh/day, so 3kW/day max may be optimistic. I put double the panels to produce 3kWh/day because moar panels.

Glad you're still with us.

 

[Hedges]

Does your life-support equipment require A/C to operate? Or can it all run off a 12V battery?
Lots of devices have a 12V jack, powered by an AC adapter.
Just be sure to include suitable fuses if you wire a power cord direct from battery.

If modest power requirements, you could implement two completely separate systems.
Besides al the lithium, MPPT, and other higher tech, you could have a second one with AGM battery, PWM, and its own panels.
The lead-acid one could just be kept floating, waiting until you need it.

In a pinch, a spare battery can be carried to the car and charged.

 

[oneandahalflegs]

Need to answer a few items.
1. I can't afford solar at this time. If I get another job I will do a system for the whole house with tesla power wall or the like.
2. I did do the audit for a larger subset before the layoffs killed that plan. Used Sense device. Need to reduce to smaller subset and post. quick review of these items from first audit was 2300Wh/day.
3. I have Propane on site. will look at conversion.
4. Jackery is my current battery which takes hours to charge. DC car adapter does not charge equipment.

 

[snoobler]

Looks like you've done your homework then.

Battery monitors:
BMV-700 = base model
BMV-702 = base with temp sensor or starter battery monitor
BMV-712 = base with temp sensor or starter battery monitor with bluetooth

If you get the temp sensor version, you'll need to purchase that separately. Not certain you need it.

The Multiplus MAY come with a temp sensor, but it doesn't have a low-temp cut off if your battery needs it. If you keep it indoors, I'm sure you'll never need it.

You'll need a VE.Direct cable to connect the BMV-7XX with the GX.

The Multiplus connects to the GX via an RJ-45 ethernet cable and terminators included with the GX.

I can't see anything else to comment on.

 

[John Frum]

@Trukinbear probably has some good advice.

 

[schmism]

The inverter style generators are fine, I have used one for my backup power for several years. If the power is out for a "day" it runs between 10 and 20 hours. In 4 years it has logged less than 100 hours. I would consider one as my second backup to keep the batteries charged. The major downside is the small ones like you listed do not have push button start and therefore do no not support autostart.

In a perfect world you would have a small 3kw? autostart propane unit that is able to have a regular exercise schedule. As a workable backup an inverter style like you list would work.

 

[oneandahalflegs]

the batteries charged. The major downside is the small ones like you listed do not have push button start and therefore do no not support autostart.

In a perfect world you would have a small 3kw? autostart propane unit that is able to have a regular exercise schedule. As a workable backup an inverter style like you list would work.

Yes, and I could even automate through Home assistant. The tiny one I bought was super cheap and a knee jerk reaction to Isaias. Better than a 400Watt inverter on a tractor ? good thing my kids were home

 

[oneandahalflegs]

Cleaned up diagram.

1. Do I really need a fuse on the battery? Battery has bms and a circuit breaker.

 

[gnubie]

It comes down to the rating and trip time of the breaker vs your wiring and the expected current of the loads. If the battery's own breaker is too high a rating and something goes wrong down stream of it, it may not actually trip or the time it takes to trip may still result in considerable damage.

 

[oneandahalflegs]

re-reviewed audit. I am going to get a 2nd set of data from the fridge with killawatt.
Looking good... I think.
Where do I power Venus GX from? Battery?

Minimum System size calculations
Full Load Wattage	965	Watts
Full Load W-hrs.	2167.42717	W-Hrs.
Inverter efficiency	94%	%
Full Load Inverter size (input watts)	1026.6	Watts
Daily Storage Requirement	2306	W-Hrs/Day
Max discharge from full CHARGE	90.0%	%
# days of storage capacity	1.0	Days
System Voltage	24.0	Volts
min Battery capacity W-Hrs	2562.0	W-Hrs.
min Battery capacity A-Hrs	106.7	Amp Hours
Max continuous current from bat.	42.8	Amps
Max Continuous discharge rate	0.40	C

 

[snoobler]

Yes. GX powered by battery.

 

[oneandahalflegs]

More, can I tie all three neutral wires [grid(earth),generator, and inverter] together at the selector switch?
Any advice for where to get selector switch?

 

[snoobler]

I would expect so. Hopefully someone smarter chimes in.

 

[Trukinbear]

How long of a power outage are you trying to plan for? You might not even need a generator, and if you do but your needs are few and far between (ie it only is cranked to recharge the batteries in the middle of an extended power outage) you may not need much generator.
I've got to question your numbers though - 2.3 kilowatt-hours per day? That is just for your vent right, and the refrigerator? The average home in the USA uses something like 20-30 kilowatt-hours per day - we're super-efficient and live in a climate that needs neither much heat or any AC so we're around 15 kilowatt-hours per day.

Mom's ventilator uses about 40 watts, as a backup backup she's got a couple of 12V deep cycle batteries and a 400-watt inverter which will run her ventilator for 24 hours without pulling the batteries down below 50% and another 10-12 hours in a real emergency situation and could be recharged with the tiniest generator you can find.

Don't even mention life support to the inverter, or generator people - most of them are NOT certified for life support.

 

[ghostwriter66]

check this video and see if any of this would help you in the design ... we have dozens of these around the oil field to help run and start equipment that is critical ... we typically put a 200 or 280aH battery on ours and it will run literally forever with a good solar panel attached ...

 

[oneandahalflegs]

How long of a power outage are you trying to plan for? You might not even need a generator, and if you do but your needs are few and far between (ie it only is cranked to recharge the batteries in the middle of an extended power outage) you may not need much generator.
I've got to question your numbers though - 2.3 kilowatt-hours per day? That is just for your vent right, and the refrigerator? The average home in the USA uses something like 20-30 kilowatt-hours per day - we're super-efficient and live in a climate that needs neither much heat or any AC so we're around 15 kilowatt-hours per day.

Mom's ventilator uses about 40 watts, as a backup backup she's got a couple of 12V deep cycle batteries and a 400-watt inverter which will run her ventilator for 24 hours without pulling the batteries down below 50% and another 10-12 hours in a real emergency situation and could be recharged with the tiniest generator you can find.

Don't even mention life support to the inverter, or generator people - most of them are NOT certified for life support.

Agreed, I may not need generator. our worst outage was 6 days many years ago. So generator is mostly for extended outages. In the winter 1000watts will run heat with generator outside this system intermittently.. I am double checking fridge with Kill-a-watt. Number includes fridge, two vents, wheelchair, and 2 computers. Expect almost two days without needing to run generator. Real world who knows.

I am wheelchair bound and have no use of my arms or hands so all of this has to be done by my wife. Extending the time between generator runs is helpful.

Whole house between seasons:

 

[oneandahalflegs]

The fridge came in at less than I estimated. 1.2 kwh/day.
Anyone have a good recommendation for manual transfer switch?

I think this is a better diagram.