Capacitor question
 

Not quite car audio related, but here it goes.
I run a large 12v to 110v inverter. Does a 110v capacitor work the same as one used in 12v applications? Sometimes a surge drawing from the inverter will cause the inverter to shut off. I have already added 12v capacitors to the power feed to the inverter, but I thought that a "starting cap" between the inverter and the 110v appliance might lessen the initial start up load. Any thoughts? What would a wiring scheme look like?

A 110V capacitor (if intended for use in alternating current systems) will actually be rated for much more than 110v, in fact 120v x 1.734 (root 3) and then add a bit of safety factor. It must be non-polarized, as alternating current cycles (reverses polarity) 60 times per second (60 Hz).

A capacitor for an automotive system can be polarized and does not need to be rated for 200 volts.

As far as a "starting" capacitor on an AC system, it would depend on the load. The more reactive the load is lagging, the more need for a a capacitor and it's leading current. However, in AC systems, capacitors aren't used for inrush currents for motors as the supply itself is supposed to take care of that, as well as be capable of dealing with events such as locked rotor (6 x FLA by CSA maximum) current, or other problems.

If you have a problem with poor supply to your AC device with your current inverter, get a bigger inverter. It's the safest way.

For a cap to work as you would intend, the duration of the current spike would have to be significantly shorter then the AC cycle your inverter runs at.... and the inductance of the cap would have to be low enough to allow it to discharge....


Bottom line is that you need to get a larger inverter as macguver suggests....

Thanks guys. I appreciate your help.
As far as a bigger inverter, its already a 5000/10000. Fortunately, it doesn't shut down because of a starting draw very often. I was just hoping for a good bolster.

Are you saying you use a a 5000 watt inverter? That's 40+ amps at 120VAC, so it should draw 400+ amps at 12VDC assuming no losses. I'm pretty sure you're not actually using an inverter that big (they exist and are as big as a large sub box), but your problem may not be on the AC side, but may be a peak supply issue on the DC side. A capacitor may help there, but I doubt it.

And a capacitor on the AC side is not going to dump current based on cycle point of the load. It works just like in DC, it resists changes in voltage and will dump current based on voltage fluctuations. In AC, the capacitor's current leads it's voltage (capacitive reactance), while an inductive load (motor, magnetics, etc.) have their current lag their voltage (inductive reactance). The capacitor's leading current is often used to balance the lagging current of an inductive load. This is called power factor correction, and is employed via capacitor banks or synchronous motors in industrial operations to aid start-up and demand billing.

In DC, voltage and current are in-phase, but a capacitor still does the same job, except the current flows one direction only (hence the use of polarized capacitors). In AC, the current flows both directions, switching at 60Hz in North America and 50Hz in Europe and Asia. AC uses non-polarized capacitors, as a polarized one will explode (with significant force, as some old-schoolers know) if connected. Not safe to do in the confined space of a vehicle unless you are 150% sure you know exactly what you're doing (everyone is 100% they know until something goes wrong ;)).

Yeah, she is 5k rms 10k peak. Its about 26" long and weighs 50lbs. It uses 2 sets of "0" gauge wire.

The real problem is not that the inverter wont support the load, but when the heavy demand is very sudden, the inverter is not fast enough to feed the load so the electric a/c compressor does not kick on.

The good news is that this only happens 1 in 10 times. It is not a huge deal, I just shut the inverter off with the remote switch and turn it back on again.

I was just hoping that 110v caps were as simple to use as 12v caps. Obviously not. I can live with what I have. It has taken me a year to get this far. I am happy to call it "good" and move on to the next chapter on my car.

Here is the exact one I am using.

5000//10000 Watt Power Inverter w/built in Charger Mode - eBay (item 130242262729 end time Aug-06-08 17:45:03 PDT)

So, how are you using this, in a vehicle, or as part of a UPS system for a house? I can't see what you would need 50A at 120v in a vehicle for, unless a welder is part of your system.

if you dont have one allready i would recomend a good battery bank with quick discharge and deep cycle to supply the power in time for your inverter that wants power NOW lol

I am using a 12000 btu window air conditioner that is completely hidden behind the subwoofer cabinet. The cold air is ducted though an overhead console to cool off the huge interior much more effectively. The condensor air is pulled in from one side of the floor and pushed out another in the rear area.

The 2 biggest reasons for a fully electric a/c is, 1st to cool off such a large interior, and 2nd, imagine you are judging a car show in Phoenix. Its 100 deg outside and you go to judge the next car. When the judge climbs in the casket shaped seat, cold air! How can that be? the engine is not running!

I would have used an RV style, but there is no way to make a roof mounted unit look "cool " on top of a twisted hearse.

I have 5 group 27f batteries rated at 900 cca ea in the car. The air won't last more than a couple of hours without the engine, but with (2) 200 amp alts, the batts bounce back rather quickly.