Automated relay question...

Not sure if this is the right forum, my apologies if not. I'm a novice when it comes to electrical stuff, and attempting to work on a home battery system. The charging source is an electric motor connected to my generator that will charge the battery bank. I wanted to find out if anyone had any ideas, could point me in the right direction on what I need in order to automate turning the motor on when the voltage in the battery bank gets low. The charge controller to the battery bank is a simple one, and only has a load cutoff, nothing beyond that. I could possibly put in some kind of timer relay, but was hoping for a more intelligent solution like a voltage range detection kind of a relay. Trying to search for what I need with limited knowledge just generates more questions, and it's very confusing with so many unfamiliar acronyms. I'm not even sure I'm heading down the right path. I would be most gracious for any help. Again, my apologies if this is in the wrong forum. Thank you!!

This is a right forum for your question, however, it would be better if you could provide as much details of what you already got. As what you wrote, I am assuming you have an electric motor, which runs a generator, which supplies power to your charger, which charges your batteries???

ELECTRIC MOTOR => GENERATOR => CHARGER => BATTERIES

If this is your layout, you have to give some specs of the above things like,
1. By which source your electric motor runs? By your house hold 230v AC or something else?
2. What is the power output of your generator? At what peak voltage? Does it produce sine or DC output?
3. What is your charger's input & output voltage?
4. What is your batteries voltage and capacity?

Then we could try to help you.
In a general way, you need to measure your batteries voltage level for a particular margin you would declare as "low battery". When that particular margin is reached, you need to activate your motor for a particular time period depending on the time required by your batteries to fully charge. Then turn the motor off and start rechecking your battery level.
And to achieve this, there are endless possibilities.

Since you want to use an electric motor to drive a generator that charges your batteries, then why don't you get rid of the electric motor and generator and use the electricity to charge your batteries??

Do I smell "over unity" here? Perpetual motion?
You cannot use the batteries to power the motor that drives the generator to charge the batteries because some of the power is lost making heat. The batteries will get weaker and weaker and weaker and weaker and .....

Genovator, yes, your assumption on the layout is pretty much spot on.

Here are the specs. Again, please excuse my lack of knowledge, experience, and education with electricity. I didn't even know what the difference between AC and DC was a month or two ago, and just barely learned what a solid state relay was last night. Attempting to deal with freezing in the winter and boiling in the summer to see if I can reduce, if not altogether eliminate the power bill. So this is a project to try to accomplish that, as well as a science experiment, as I have found this all very fascinating, and has really peaked my interest in learning a ton more. We take electricity for granted every day, until it goes out, or the bill comes, and your wallet is suddenly under attack.

1. Electric motor source will be house power, via a variable voltage transformer that is plugged in, running at about 50-55v to the motor. Electric motor is an old 1/2 hp washing machine motor, 8 amp (9-12 start?), with a start capacitor. House is showing 122v from the outlet.

2. Generator is a home grown version, used about 20 pounds of magnet wire in 8 air coils, with 16 rather large magnets running over them. I've been able to successfully test it, and read about 115v. The plans indicate it spits out about 1400 watts, but due to the change in those plans, have no idea what it's capable of. Is there any way to test the limits, other than to run a load, and see where it fails?

3. The charger is a 30 amp charge controller. Will I be able to hook directly up to that from the generator without having to reduce the DC voltage going in? One of the other parts I'm not certain about. One of the other concerns was whether there would be enough power for the charge controller to do it's thing.

4. The battery bank will consist of 3 x 12v deep cycle 260 amp hour batteries.

With this info, is there the best way to approach this to do a "timed" approach? The charge controller will obviously control all the charging, and protect the batteries from over charging. At the same time, I want to reduce wear and tear on moving parts of the generator, so not sure if there's a way to have some kind of a relay sense when it's low, turn on the power to the motor, and then turn off when a certain voltage has been achieved?

Thank you for any help, it's always extremely appecicated!

Genovator said:

This is a right forum for your question, however, it would be better if you could provide as much details of what you already got. As what you wrote, I am assuming you have an electric motor, which runs a generator, which supplies power to your charger, which charges your batteries???

ELECTRIC MOTOR => GENERATOR => CHARGER => BATTERIES

If this is your layout, you have to give some specs of the above things like,
1. By which source your electric motor runs? By your house hold 230v AC or something else?
2. What is the power output of your generator? At what peak voltage? Does it produce sine or DC output?
3. What is your charger's input & output voltage?
4. What is your batteries voltage and capacity?

Then we could try to help you.
In a general way, you need to measure your batteries voltage level for a particular margin you would declare as "low battery". When that particular margin is reached, you need to activate your motor for a particular time period depending on the time required by your batteries to fully charge. Then turn the motor off and start rechecking your battery level.
And to achieve this, there are endless possibilities.

Click to expand...

It sounds as though you want to test your backup power supply, correct?

Otherwise you might as well charge the batteries from house power (as AudioGuru suggests).

A simple op amp with hysteresis will detect when the battery bank is low. At 10.5V the output turns on.
At 14.4 V it turns off (typical cycle for a 12V system).



The zener diode can be any value. The simulation has a 5.6V.

Adjustment is tricky. If you use a comparator instead of an op amp, then you would switch a few components around.

Hey Brad, I appreciate your response.

However, my eyes glazed over hitting "op amp with hysteresis", and "zener diode", and looking at what appears to be an electrical diagram?? I'm so far out of my element right now, it's like Mt Everest. :-\ Keep in mind, I didn't even know what the symbol for AC and DC was until two months ago, have had no classes or training or education, other than what I've been able to google. And trying to google anything technical like an op amp with hysteresis, I'm doing good to just find op amp, and looking at a wiki definition of it, it might as well be greek. There any way you can dumb this down for me?

BradtheRad said:

It sounds as though you want to test your backup power supply, correct?

Otherwise you might as well charge the batteries from house power (as AudioGuru suggests).

A simple op amp with hysteresis will detect when the battery bank is low. At 10.5V the output turns on.
At 14.4 V it turns off (typical cycle for a 12V system).



The zener diode can be any value. The simulation has a 5.6V.

Adjustment is tricky. If you use a comparator instead of an op amp, then you would switch a few components around.

Click to expand...

There is a chance your charge controller has an output terminal which could control a relay. It starts charging when the battery drops to 10.5 V, and stops charging at 14.4 V (approximately). It just so happens that you want the relay to activate in sync with the controller. The instructions will tell what is possible.

Of course the controller needs to have power in idle periods, so it can detect battery voltage, and turn on a relay.

As for my schematic, it shows a 'voltage range detection kind of a relay', as you referred to in your initial post.

The op amp (operational amplifier) is the most useful and versatile device, and easy to use, which can be made to respond to your battery volt level, and switch a relay on and off.

An op amp is contained on a single IC. Typical price less than a dollar.

Hysteresis is the method to create one level for switch-on, and another level for switch-off.

I once looked at many charge controller schematics, while I was constructing my own backup home power system. I don't recall seeing any with a simpler method than to use op amps in this role.

It may be possible to find a ready-made unit for this purpose, if you check catalogs from suppliers of home power equipment.

If you really want to make this thing simple for you, I would also suggest not to use motor & generator. As you stated, your generator produces around 115v, then maybe your controller supports 220v household supply. You have to see what is your charger's input voltage. If you are not sure about your charger, can you look into any printed label on it? And if it hasn't one, you can open it to see its circuit. Until you are sure if all parameters match with each other, you cannot hook them up. But as you said its a 30A charger, it can charge 260Ah battery pack very well. I guess your batteries are connected in series (12+12+12=36v)...
Is there any specific reason to convert electrical energy to mechanical, then again to electrical???
The most simplest one will be to plug in your charger to your house supply (if it supports).

You mentioned that your idea will save money because maybe the electricity your motor and generator produce will cost less than the electricity from your electrical utility company. IMPOSSIBLE!
Your transformer gets hot, your motor gets hot, your generator gets hot, your charge controller gets hot and the battery also might get hot. The heat is WASTED electricity that you have paid for.

A battery is used to supply electricity to an inverter in a home in a third world country where electricity is frequently cut off because there is not enough electricity available for everyone.

A battery produces DC, but almost everything in your home runs from AC. Your battery is 36V but almost everything in your home uses a much higher voltage.

You did not say the battery will power a DC to higher voltage AC inverter. It will also waste expensive electricity by getting hot.