Solve this Mystery.. Overload?

[skew]

Somehow my power inverter has fried a power amplifier and perhaps the alternator.

The setup
A 4 channel power amplifier, a 2 channel power amplifier, and a 1kW power inverter are connected in parallel via an electronic battery isolater to a >1 y/o expensive AGM battery. Supplied power from alternator is aprox 140A.

With the audio system completely shutdown yet still electrically connected to the power supply in parallel, the power inverter was used to power a heavy inductive motor. Namely a DeWalt Mixing drill that draws 7A@120v. Since the drill does not feature a varible speed, and reduced speed was required, analog reduction was performed by quickly engaging and disengaging the trigger switch. *click*click*click - *on*off*on*off.

After stopping to change drill bits, current (or voltage) will not flow. Engaging any tool only makes the tool start for a fraction of a second. Thats it.

I have not completed diagnostics, but this is what I know:

The amps were 'sort of' working for a while after the event, though not properly. disassembling the system so far has revealed the 4 channel amp connected to and industrial bench supply seems ok, the 2 channel amp flashed blue light when in vehicle but red when connected to bench supply.

Inverter has not been tested. Battery has been charged, but not tested alternator has not been tested, crossover other audio components have not been tested. Its worth mentioning that I rebuilt the entire alternator last year with the exception of the diode pack. Scoping the alternator doesnt reveal anything unusual.

I need to know what cause this fault. I can repair/replace, but I cannot let this happen again.

I thought I was ok to use the inverter with the audio system off.

Thanks for any expert advice

 

[rjenkinsgb]

A typical motor such as in a drill etc. can draw several times more than its rated power when initially starting.

6x higher current is not at all unusual. It's a very common problem when running such as that from an inverter.

You could add an inline drill speed controller, that should allow a gradual start to avoid the excess current and inverter trip.

 

[Lightium]

Without looking at the numbers I've fried the inverter when applying intermittent power to the drill by clicking on the trigger.

 

[Diver300]

There are a number of elements in the system that may produce problems.

1) The alternator will not be able to change the output current quickly. Look up "load dump"
2) The drill will take a lot of current when starting, and may do strange things when powered up when already spinning
3) The drill will take current at a poor power factor, either with a lagging current or with a current that is very non-sinusoidal or both
4) The inverter will take more current if the DC voltage drops.
5) The surge current taken by the drill will be more than the rating of the inverter.
6) A non-sinusoidal current waveform may mean that the inverter is effectively overloaded during part of the cycle even when the drill is a t full speed
7) If the current waveform taken by the drill is lagging, that means that power will be put back into the inverter for a short time during each half-cycle of the supply, which the inverter may not handle well.
8) There may be much of the power amplifier circuitry which is in use even when the sound is off.
9) Many power amplifiers have inverters in them to boost the voltage. The on-off-on operation may result in a surge current, and the circuitry that reduces surge on turn on will not have had time to reset if the voltage drop is brief.

My suggestion would be get a vehicle that has more electrical power and is designed for powering large AC loads.

Ford F-150: Power dispenser with V2L function - Newsy Today

Ford F-150: Power dispenser with V2L function

www.newsy-today.com

 

[skew]

Thanks for the reply. surge current, I had no idea it was that great.

I generally use the inverter 3 or 4 times a year. In this instance it was to save me the trouble of rolling out 250 ft extension cord. Even when it is used its generally a laptop, glue gun, television, small power tool.

The parallel connections were a matter of convenience, since only one is used at a time. I could install a battery isolator to protect the audio system, but I'm more concerned with the vehicles electrical system.

Shame the rectifier is internal, else I could pump the AC to where its needed, install an isolation transformer, then rectify it discreetly for individual applications...

 

[skew]

7) If the current waveform taken by the drill is lagging, that means that power will be put back into the inverter for a short time during each half-cycle of the supply, which the inverter may not handle well.

oh wow, I never thought of that. and my on-off-on-off forced it to dump half the current each time. Still with the amps powered off I cant imagine how it affected them.

FWIW, the power amp in question is an Alpine PDR-M65. A little over 1yr old. Single install. generally not used over %40 rated @ 4ohm bridged.

Again electrically connected, but OFF.

 

[Diver300]

To get 1300 W into 4 Ohm, the amplifier has to be producing ±25 V. There has to be an inverter to produce those voltages. It's not so far different from the inverter that needs to produce ±160 V or so.

It's quite possible that the inverter that produces ±25 V runs whenever the ignition is on.

 

[skew]

hmm, I think there has been some misunderstanding. Apology if I was unclear.

There are two 12v Alpine Car Audio Amplifiers, and one 1kW inverter. The battery power supplies are all wired in parallel. The Audio amps are connected to speakers.

When I use the inverter the entire audio system (radio, amps etc) is powered OFF; however electrically, the audio amp have 12V at the terminals, this is normal since the 12V REMOTE wire controls the ON function.

I am deducing now that that the surging from the on-off-on-off of the drill probably kept dumping current and the input filter caps & diodes on the amp are likely toast.

 

[Lightium]

Correct. Also next time have an inverter 4 times the current when powering inductive loads.

 

[skew]

Absolutely, thank you. I was not aware of that. Though I wont feel comfortable until I isolate the systems.

It goes without saying the alternator diode may be toast aswell. Voltage reads ok, but may fail a current test.

 

[Lightium]

There should be six diodes welded in place.

 

[Lax Luthier]

Use a cordless, DC powered drill/driver next time. AC induction motors are rough on inverters. It's not a good match. In addition to their initial starting current being locked-rotor current (essentially a short circuit when started), they can produce substantial amounts of counter EMF while running and especially when they are switched off.