connecting an inverter: spark prevention / reduction

[pellicle]

when I attach an inverter (turned off, unloaded) to my battery system there is an inevitable inrush of voltage to fill the capacitor. I wonder what is the best way to do this and reduce this spark. I've read of people using a 0.1Ohm resistor, which I assume is sufficient to slow it down. Before I get one, does anyone have any views on a 1ohm wirewound resistor for this task? (cheaper than a 0.1 ohm)

My intention is to make the connection using the resistor as a "probe" then follow through with the actual connector in short order.

Thanks

 

[Abodyofscience]

It's an inrush of current to charge the capacitor.
Your battery's internal impedance probably limits this current so you then have an RC ckt.

V ---R----|
...............C
................|
............ground

With an ideal battery instantly connected to a capacitor, the current would be infinite, for zero time, IIRC. It's called an impulse function.

Why is this short term, high current inrush a problem?

"My intention is to make the connection using the resistor as a "probe" then follow through with the actual connector in short order."

Called a "soft start".

 

[400bird]

1 ohm may be significantly lower than needed.
But ohm's law means that your battery voltage will help ID the correct resistor.

I've used both 4 and 50 ohm resistors

 

[Bud Martin]

when I attach an inverter (turned off, unloaded) to my battery system there is an inevitable inrush of voltage to fill the capacitor. I wonder what is the best way to do this and reduce this spark. I've read of people using a 0.1Ohm resistor, which I assume is sufficient to slow it down. Before I get one, does anyone have any views on a 1ohm wirewound resistor for this task? (cheaper than a 0.1 ohm)

My intention is to make the connection using the resistor as a "probe" then follow through with the actual connector in short order.

Thanks

Just go to car store and get the 10 Ohms 10W ~ 25W resistor they sell to be used with LED lamp conversion. 12V/10 Ohms will limit the current to 1.2A if it is 12V system.

 

[Minimoose]

I just use one of these. The light bulb acts as a resistor. When the light goes from bright to dim or completely out you are good to go. Of course this applies to my 12 volt system.

 

[rmaddy]

Will has a video on this:

There is also the following in the Resources section:

Inverter Disconnect Switch with Precharge

To get the paper, click on the orange button at the top of this page. This circuit is designed as a disconnect switch that allows the user to pre-charge the inverter capacitors before turning the switch completely on. 26 June 2020 update: At...

diysolarforum.com

And there are many existing threads on setting up a precharge resistor.

 

[pellicle]

And there are many existing threads on setting up a precharge resistor.

Hi
perhaps its related to not knowing the appropriate key words, but when forming the topic many suggestions appeared. I ran through some of those and wasn't entirely sure of the limits

 

[pellicle]

It's an inrush of current to charge the capacitor.

yes, you're correct. I should have been more carful in my words. I'm getting sloppy

I'm actually pretty familiar with this on another area, this is a blog post of mine from a few years back written to clarify why instructions on scooter / ebike charging were often mistaken

Charger sparks

Some question recently about charging and chargers and when and how to plug your charger in to your scooter prompted me to write this. The s...

cjeastwd.blogspot.com

 

[pellicle]

I just use one of these. The light bulb acts as a resistor. When the light goes from bright to dim or completely out you are good to go. Of course this applies to my 12 volt system.
View attachment 85666

and why the hell did I not think of that!!

thanks ?

 

[curiouscarbon]

another option is XT90 plug with anti spark

if it can handle the total current then no steps needed, since there is a precharge anti spark resistor built into the plug.



this one is 5.6 ohm (green mark)

Anti spark connectors XT90 resistor integrated

has anyone used these before? integrated resistor that contacts first before the full connection. https://www.amazon.com/Pigtails-XT-90S-Connector-Silicon-Battery/dp/B083SC9P71/ seems kinda neat. never tried it myself. dunno what the resistor value is. if i get one i’ll try to measure that...

diysolarforum.com

 

[Mountainlion]

I watched Will on one of his Youtube videos. His recommendation was to use the resistor on the negative side?

I have always done on the positive side.

Does it matter?

 

[rmaddy]

I watched Will on one of his Youtube videos. His recommendation was to use the resistor on the negative side?

I have always done on the positive side.

Does it matter?

Mine's on the positive as well. It shouldn't make any difference. The whole idea is to complete a circuit with minimal current to slowly charge the capacitors.

 

[time2roll]

I watched Will on one of his Youtube videos. His recommendation was to use the resistor on the negative side?

I have always done on the positive side.

Does it matter?

Is there an order to connect the DC power cables mentioned in the manual? Final connection gets the resistor.

 

[32 volt boater]

I thought that was normal a big ass spark. Connecting my big outback 32v inverter its just pop! No way that big spark could be good for anything.

I am going to use a halogen lightbulb as a resistor. Got a crusty old work light, going to extract the socket and bulb mount on aluminum backing make it look cool like it belongs.




I don't think those marine battery switches are made to endure that spark that comes with turning big inverters on and off.

Ohms Volts Watts Amps Converter | Enter Any 2 to Get Other 2

Calculate watts from volts and amps, amps from volts and watts, and ten other conversions. Result includes Ohm's Law formula and step-by-step solution.

www.free-online-calculator-use.com

That seems about right, 5 olms.

 

[32 volt boater]

I plugged in 32v and 5.12 olms and got 6.25 amps. Any old switch can deal with that.

Guess I will put a momentary push button switch.

 

[Bud Martin]

I thought that was normal a big ass spark. Connecting my big outback 32v inverter its just pop! No way that big spark could be good for anything.

I am going to use a halogen lightbulb as a resistor. Got a crusty old work light, going to extract the socket and bulb mount on aluminum backing make it look cool like it belongs.

View attachment 107217


I don't think those marine battery switches are made to endure that spark that comes with turning big inverters on and off.

View attachment 107218

Ohms Volts Watts Amps Converter | Enter Any 2 to Get Other 2

Calculate watts from volts and amps, amps from volts and watts, and ten other conversions. Result includes Ohm's Law formula and step-by-step solution.

www.free-online-calculator-use.com

That seems about right, 5 olms.

300W/120V = 2.5A, how does it get 6.25A?
So Hot resistance of the incandescent lamp will be 120V/2.5A = 48 Ohms, the Cold resistance (about 10 ~15 < Hot resistancce) will be about 4.8 Ohms, you can easily verify with Ohm meter. Incandescent lamp has positive coefficient.

BTW, when perform the pre-charge, make sure the power switch of the inverter is in the OFF position.

 

[32 volt boater]

300W/120V = 2.5A, how does it get 6.25A?

BTW, when perform the pre-charge, make sure the power switch of the inverter is in the OFF position.

I plugged in 32 volts, what I am using, instead of 120.

 

[Ellcon123]

Mine's on the positive as well. It shouldn't make any difference. The whole idea is to complete a circuit with minimal current to slowly charge the capacitors.

Good practice to connect +ve first so resistor would be used on -ve. Battery -ve is often tied to earth or chassis. Dropping the -ve is much safer than +ve. Good example is jump starting a car. Almost everything in the engine bay is -ve so you don't want to drop the +ve lead in there!

 

[32 volt boater]

Outback FX series no on - off switch comes with it. Its a wire in option. That I should do.

What happens bad if the inverter is on when charging caps with resistor ?

 

[Bud Martin]

I plugged in 32 volts, what I am using, instead of 120.

But is that 200W 32V lamp instead of 300W 120V lamp as shown in post #14?
The cold resistance of the lamp will be 10 ~ 15 time less than the calculated Hot resistance.