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Cheap Homebrewed Backup Power Supply
By srnoth, Section Homebrewed Electricity Posted on Sat Oct 02, 2004 at 10:08:47 PM MST
The best way to create a backup power supply using stuff hanging around the work room.

Hey there,
I just found this site a couple of days ago, and I want to say how wonderful it is for all this very useful information to be readily available.
I am not new to this sort of thing, having blown two UPSs (smoke and all), fried a cars electrical system, and run a couple 12v lights of my dad's old truck battery, but I only recently started to seriously work on a backup power system.
Where I live, on the edge of a forest, there is grid power available, but the power runs on one line up my street for some distance, and the line is very old, so my grid power is not very reliable. When it rains heavily, the power can go out for a couple hours, and this happens frequently enough for me to be annoyed enough to start building a backup power system.
I started by hooking up an old APC UPS rated at 300w to the car battery, and running the car so I would get the power from the alternator. This worked quite well, and, by running an extension cord out the window to the car, I was able to power a couple lights. This worked for very short time periods, but one night when power went, and I had been running about 4 lights off of it for about an hour and a half, the lights flickered and went out. When I looked outside, smoke was pouring form the UPS (not good!). Then, to add to the destruction of my UPS, in my haste to disconnect it from the car, the I accidentally touched the live to the body of the car, and instantaneously melted the wire going from the alternator to the battery (Even worse, it was my mother's car!!) So that put a hold on me using cars as my generator.
The next thing I did was to buy a used alternator from a used car parts store. I got one for about $15, which I thought was a very good deal. I connected it to an old Brigs 5 Hp Pump engine I had hanging around. This did work, but the engine was way too loud, and it vibrated so much that the whole contraption would come loose quite frequently. All in all, I could have made this work (about 5 alternator, a car muffler, a sound proof cabinet and a 3000 watt inverter would have worked), but it would have been too expensive and time consuming.
After a bit, the idea of using a car came back to me. It would solve all my problems. A car runs almost silently at idle, and still develops enough horse power to power a half dozen lights, a TV and a couple computers. This was perfect. In the year that had past, I had regained my parents trust around cars, having convinced them that I had learned my lesson. So I set about developing a cheap, durable power system.
The base of my system was a small breaker panel that my dad was no longer using. It was designed for two phase electricity, so I joined the two phases, there by letting me use the main breaker to control two inputs separately. I connected one half to a used car battery using old, thick jumper cable. I then connected the other input to a jumper cable that could connect to the battery on the car. Because the cables had to be about 8' long to reach the car, I used three jumper cables in the live and three for the neutral. Even with this, I still get a voltage drop of about half a volt when sending about 40 amps through these cables.
I then used the various smaller breakers to connect two 12v ordinary light bulbs, two old UPSs (I made sure to use fans to cool them), and soon a 400W inverter.
And so this is my system so far. When power goes, I can use the battery to power the two 12v light bulbs while I connect the cables to the car (no more messing about in the dark with batteries that can deliver 100 amps instantly). Once the car is running and connected, I can turn on the UPSs (one is too small to power a computer, so I have it powering my network hub and DSL modem, and the UPS part of the other is blown, so only works as an inverter) and the inverter, and run extension cords to whatever I want to power. Any thoughts?
So that is where I have reached. I am now running wiring to the rooms in my house where I will want backup electricity, and I have installed florescent lights in the living room, kitchen, bedroom, study and bathroom, since florescent lights are much more power efficient. That is proving simple enough, but I have the following problems to figure out:
I need to find someway of turning the 400 watt inverter into a UPS, for my computers, and I need to create a circuit that turns the florescent lights on when power goes. I also need to improve my battery bank.
About the UPS, I was wondering whether I can just use a relay, controlled by a 12v adapter, so that when the power goes, it no longer receives the 12v, so it switched the 115v supply from the mains to the inverter, which will be left on permanently. The relay in my broken UPS is still working, so could I use that to do this? I have heard about problems with the mains and the inverter not being in phase, and creating power spikes and dips when it switched. However, I have also read on this board that the very minute break in power while it switches solves this problem. Does anyone know what the real answer is?
About the auto-on lights, I was thinking that I could use a similar circuit to the one in the UPS, except it would not need to be a heavy-duty relay, since I could just use it to operate the switch on the inverter. Any thoughts?
About the battery bank, I am planning to get one ore two 100 amp hour automotive batteries, and use the built-in charger on one of the UPSs to charge them. Two questions:

- Do these batteries need any special form of ventilation, or can I just put them in a cupboard?
- Will the built-in charger damage the batteries, and will it charge them properly?
Any thoughts?
I also have some projects in mind for the future:
*A home made perfect sine wave UPS for sensitive equipment such as computers. I plan to get a whopping 50 amp continuous battery charger, maybe homemade, a car battery, and a 400 watt sine wave inverter. This way, the charger would be continuously charging the battery, and the inverter would be continuously converting the 12 volts into perfect electricity. This way there would be no breaks in the supply when power goes, and no fluctuations in the voltage and frequency. Long live my computers!
*Run a new electrical system throughout half my house, connected to a modified sine wave 3000 watt continuous UPS/inverter, connected to at least 10 100 amp-hour batteries. How's that for making the neighbours jealous. If I did this, I would also like to get a diesel engine connected to about 10 automotive alternators. And as much silencing as possible. Also a 12v water pump, so I can get water from the tanks when power goes.
Now that is my dream backup power system. Maybe some solar power as well!! All your thoughts on everything here are appreciated greatly.
Stephen,
15 year-old student,
Trinidad, West Indies.

Cheap Homebrewed Backup Power Supply | 12 comments (12 topical)

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#1)
by Jerry on Sat Oct 02, 2004 at 10:48:01 PM MST

Hi Stephen.

I just want to say one thing.

Fuses,fuses,fuses,fuses and more fuses. You would not want to repeat the burning wire thing in the car as the burning wire thing in the house. Fuses need to be just a pinch higher amperage of each circut you build and they must be located at the battery power source and both on the power going in and out of the invertor. Make surew wire sizes are big enough for there load. There are wire ga. load and distance charts on the net.

Your perants may not give a second chance on there house.

Good luck and keep up that enthusyazym (spelling?).

JK TAS Jerry

Airheads Page

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#2)
by justanotherguy on Sat Oct 02, 2004 at 11:17:41 PM MST

wow sounds like you are well on your way to ending up looking like this

there are so many things that scare me in your post i don't know were to start. first off is the breaker panal and the breakers in it dc rated??? if not the contacts in the breakers will weld closed and will do you no good in an overload situation... or the panal could just up and catch on fire....

i would go back the the 5hp engine and alternater idea trying to use a car is going to end in car repair bill round 2.

i will let someone else comment on the rest s it is late and i am tired...

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#3)
by Roamer195 on Sun Oct 03, 2004 at 12:27:44 AM MST

Here's a much more flesh-friendly option. :)

Buy yourself a few deep-cycle batteries and a marine "float" charger. Car batteries are utterly destroyed by deep-cycling. They're only built for short-duration, high-current loading, then immediate recharge.

Wire all the batteries in parallel with a heavy buss cable and connect the charger to those with solid bolted connections (no suprise arcing from battery clips)

A 100ah battery will allow you 5amps (75 watts) continuously for about 15 hours without damaging the battery. Mulitiply that by however many batteries of the same kind you wire into that parallel bank. Those are about $60 each from wallyworld.

Based on those numbers, build it large enough to get you through blackout periods without needing any outside generators.

Then just recharge the bank when the power comes back on.

Add a small generator to recharge the bank during extended blackouts.

Don't mess with the house breaker box until after you take an electrician's course.

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#4)
by bob golding on Sun Oct 03, 2004 at 09:02:08 AM MST

as pointed out recently on here you dont need a pure sinewave inverter for a computer. they all use switch mode power supplies which dont care too much about waveform or even voltage. the only thing i can think of that might need one is anything with an inductive load or a motor like a fridge. i would forget using the house system altogether and make a totally seperate system. try and find a local electrician to help you design it. good luck.

bob golding

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#5)
by srnoth on Sun Oct 03, 2004 at 06:07:09 PM MST

Hey guys,

Where did you get that horrible picture??? What on earth did that?

That is enough to put anyone off doing anything with electricity :-).

I did read about AC rated breakers arcing and welding together, and I most certainly will install some fuses on my battery and alternator cables. I have experimented with using normal AC fuses before, and I had success, where a 15amp breaker would let one 100W light bulb through, but would trip after connecting two of the light bulbs. Please note that if I did connect a 3000w inverter, I would most certainly not use an AC rated breaker for that kind of amps! I do take chances, but I have been shocked and burnt enough in my relatively short lifetime to have a respect for large amounts of electricity.

I am trying to run as little 12v wiring inside the house, since I most certainly would not want burning wires inside the house. I have my 12 panel right next to the window, and that is as far as the 12v wiring goes. I have also been giving the system test runs for about an hour, in the daylight and with grid power, and monitoring everything for over-heating and such.

About a car repair bill in round 2, hopefully not. I am finished with messing around deep inside the engine (no more connecting wires directly to the alternator and such). I just connect the leads straight to the car battery, and I will install fuses on both of those lines, so that it will be near impossible to damage the car. The Brigs engine just makes too much noise. I have exams coming up this year, and so I don't have that much time to work on this project. Maybe next summer I'll get the 5Hp engine setup working properly. My only question with using the car is if the car's alternator is rated at 85 amps, will sucking 60 amps from it for 3 hours straight damage it? I have already checked the engine for overheating, and that is not a problem.

I am still thinking about my battery bank. Where I am, car batteries are much cheaper than anything else, so they were my first choice. The basis for my system would be that it could only power a computer, tv and a good few lights for a short period of time, and if I needed to use these appliances for longer, I would have to use an outside generator. I read on this site that batteries are not damaged if you only discharge them by 20%. Does this also apply to car batteries?

Also, I have no intension of doing anything to the house's existing breaker panel and electrical system. I may have some experience with electricals, but I am not a registered electrician, so that would be asking for trouble ;-).

Thanks for the advice about the sine wave invertors. I would not want to buy one unnecessarily as they seem to cost about 10 times an ordinary modified sine one would cost. By the way, I got a Vector 400w continuous 800w max refurbished modified sine wave inverter from Amazon for $20 bucks. Was this a good deal?

Thanks for all your help (and sometimes gory advise!!),
Stephen.

[ Parent ]

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#7)
by justanotherguy on Mon Oct 04, 2004 at 01:22:16 AM MST

"Where did you get that horrible picture??? What on earth did that?"
do a google image search for acid burn you will find pics nastyer than that. was trying to convay the point that if you short a battery and it explodes you gonna end up with a face that not even your mother could look at without wanting to vomit. play safe be very carefull or you will pay the piper.

[ Parent ]

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#9)
by elvin1949 on Tue Oct 05, 2004 at 09:38:08 PM MST

ya'll all pay attention to that.
i learned the hard way, 25 yr's ago
a battery blowing up in your face when you are working alone,and 100 ft through a minefield of junk to the closest running water is no fun.
almost cost me my eye's.
BE CAREFUL
later
elvin

[ Parent ]

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#6)
by nothing to lose on Sun Oct 03, 2004 at 10:41:14 PM MST

Wow long post and so much stuff, This may be a long reply too :)

First though I am not familar with your country, pricing, or whats available to you.

"I started by hooking up an old APC UPS rated at 300w to the car battery, and running the car so I would get the power from the alternator. This worked quite well, and, by running an extension cord out the window to the car, I was able to power a couple lights. This worked for very short time periods,"

You say 4 lights? How many watts was that? Also it's not good to idle a car engine for long periods plus all that waisted feul.

You might just want to take the easy way out on this. Take a nice large UPS (I have a 600watt) and connect that to several deep cycle batteries. When grid power is on your UPS is running on that and charging the batts., When grid power is off you have the UPS running on the fully charged batteries. No problem switching stuff. Make sure you wire the UPS to the correct voltage of batts. Mine is 24Vdc so I have 2 batts. each 115 amps wired for 24v which is still 115amps. If you decide you need more time, then wire in more batts. in my case two at a time.
I also have much larger Ups's here, but I only do that with the 600watt one for now.

I also have a 5,000 watt/10,000watt surge Aims inverter and other battery systems for it.

Basically since your not wantng to get off grid and make your own power like many of us, just wanting backup power, I would say stick to the UPS systems. Get larger ones and several of them. Should be cheap if you can find them used needing batteries. Then you have the charger/inverter and instant switch between grid and batts. Add your own deep cycle batteries to each one. Then you also have the choice of which to run things off of. Maybe one UPS for the computer only, another for a light, stereo and a clock. Heck you could even have one in each room if you wanted, and no problems wiring, just put batteries outside and run the 12v wires of heavy enough size and a fuse, plug into wall and forget it. Figuring each UPS has it's own battery set. Otherwise you could also run one larger set of batteries and run wires from that to each UPS. Run them all fromthe same batt. bank, but that might be more problem as you would need heavier wire for longer runs, might have to disable the chargers in some UPS's ect...

Car batteries as others have said are meant to be kept fully charged all the time basically. They give out a little power to start the car and then go back to full charge where they should stay. Basically when everything is working correct and the engine is runing you don't even need the battery in the car! The car runs from the altenator, not the battery. The battery is kinda a buffer, takes the juice and stores it, and supplies extra durring surges till the altenator catches up. Take the Hot wire off the battery when the car is running and it should keep running unless you over load the charging system. I have driven many cars without Batteries, push start a manual transmision car and start it in gear and go.

Deep cycle batteries like for trolling motors on fishing boats and other types are meant to be charged for awhile, then used long periods without charging. Like a trolling motor, you charge over night then use it alot while fishing durring the day, then charge again that night. Deepcycles are built heavy inside to handle that type of use, car batts. are not!

As for your Idea of using the Brigs engine and an Altenator for a generator, that is a good idea! I have done that myself. I suggest taking the exhaust and making a better muffler to quite it and use that. For one thing running a car engine is going to use way too much gas for the power you'll be getting. The small briggs engine will produce plenty of power but really use far less feul! Many cheap fast easy ways to quite that too. Connect a pipe to the engine exhaust and run it into a heavy plastic barrel of dry loose sand. The sand absorbs much of the noise, it's loose so the exhaust passes right through. Maybe just run the pipe into a barrel of water, that works too. Just make it below the engine, you don't want to suck water into it if a valve sticks.

As for the vibration though. Many motors of that type use the blade weight as a flywheel, if off a push mower could have been your problem. Use a heavy pully bolted where the blade used to be, or use a riding mower type engine which might be better. Mine was a 12hp riding mower engine. If it was a horizontal motor like for a minibike or gocart it should not have had much vibration anyway. Bolt it all nice and tight to a frame. For mine I used a braket I made for the altenator, it had one bolt to the frame to hold it in place on one side and a very heavy spring on the other side to pull it tight against the belt. Easy to remove or adjust when I was palying with things. Course there were other parts to hold it lined up that it slide against.

"I need to find someway of turning the 400 watt inverter into a UPS, for my computers, and I need to create a circuit that turns the florescent lights on when power goes"

I would suggest getting a real UPS for the computer. Wire the 400watt inverter to battiers and just turn it on and off as needed. As for the instant on lights, take a
light sensor like turns on the outside lights at night and connect the lights to that. Put the sensor in a dark box, connect to the UPS. Then take a small light (smallest low power you can get)and put that in the box with the Senser and plug it to the wall. When grid power is on, light is on, senser sees light and flouresents on the UPS are off. When grid power goes off, light goes off, senser is in dark and turns on the UPS powerd lights.

Good luck, be creative but be safe, and have fun!!
.
nothing to lose

Spelin and tpying are my strong points, not electronics.

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#8)
by juiced on Mon Oct 04, 2004 at 09:21:08 AM MST

15?!

Wow, cool man.

You know, not to try and divert attention from this site but i would like to see you @ my site. The reason for this is my main goal is to bring alternative to mainstream. People in your age group are one of my 'targets'. Im 26, so im not tooo far off. hehe

I really respect your drive for knowledge; never stop asking questions.

Canada's -Debatable- A.E./R.E Debate Site
News, discussions and debates!
www.juiced.ca

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#10)
by jacquesm on Thu Oct 07, 2004 at 07:29:01 AM MST

Hm, my advice to you is very short:

STOP WHATEVER YOU'RE DOING AND FIRST STUDY THIS STUFF

You are very likely going to get yourself either hurt or killed the way you are going about it. I'm all for experimenting, but batteries, crappy power lines, UPS's and running car alternators do not mix very well when you're experienced, when you're inexperienced you're likely to end up as a darwin award nominee.

Please trust me on this, I have been where you are right now, being 15 and pulling all kinds of crazy experiments. But at least I had a solid understanding of the basics and how to operate safely and from your words I gather you really do not.

Find yourself a friendly neighbourhood ham and become his disciple, he'll be more than willing to teach you whatever you want to know.

If all you want is to be able to deal with power outages, go buy a generator and have it wired in by a competent technician.

If in spite of this advice you want to push on with your unsafe activities, at least go visit a lawyer or notary public and leave a will.

good luck

Jacques Mattheij

www.greenbits.com

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#11)
by srnoth on Fri Oct 08, 2004 at 09:20:00 PM MST

Hey again,

I just want to let y'all know that I appreciate your advice and warnings especially with regards to my own safety. I am sorry if my original post may have made me sound like a bit of a lunatic, just throwing caution to the wind. I have no intention of injuring or killing myself or those around me, and this is why I have come to this site.

I would also like to say that as far as my basic knowledge goes, I have been delving into electronics since I can remember, and I have been 'tutored' under my father, who is a construction engineer and has been involved with professional electrical installations for years. I have also spent some time learning from several of his friends who are professionals in the area of electrical and electronics. And on top of this, I have been installing 115VAC wiring and lights for a good few years now, all being done safely.

Also, I am not going at this thing in one mad dash, plugging things in and seeing if they work. It is an ongoing project that has been taking place for several years now. And I have been doing research before I make any future developments.

Good. Now that that's over, I have taken y'alls advice and got my dad to purchase 2 UPSs for the computers. I will then hook these up to a battery bank for power when electricity goes. I will also use a couple cheep 12v computer fans to provide adequate ventilation for them.

Tomorrow I will be checking local companies to find out the prices of good, deep-cycle batteries, such as those used in fork-lifts. This way I will not have to worry about replacing batteries too often.

Also, I will be getting some heavy duty automotive fuses for all my power sources. I have one question about this. If I am unable to get say 100amp fuses for my batteries, will say 2x50amp or 4x25amp fuses work?

Thanks again for all your advice,
Stephen.

[ Parent ]

Re: Cheap Homebrewed Backup Power Supply (3.00 / 0) (#12)
by ghurd on Sat Oct 09, 2004 at 10:50:38 PM MST

It is common for some inverters, etc., to use 2X50a or 4X25a fusing.

The local auto parts store should have 100 amp fuses. They are a little goofy looking compared to what most people are used to seeing. I don't know what kind of holder they go into.

There is also a Maxi-fuse, maybe thats a brand name, but it looks like a blade fuse only much bigger. I think I've seen them in 60 and 75 amps, probably many more.

G-

[ Parent ]

Cheap Homebrewed Backup Power Supply | 12 comments (12 topical)

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