1st Degree Felony Alternator Abuse

I recently put up a thread that began about velcro but last landed on this:


I figured I would ask: what is too much in terms of peripheral (ie added to stock) electonics?

I have run (ie on and charging) through various USB ports two cell phones, a tablet (for nav) and two kids tablets in the rear seats (I installed USB ports at the back of the center console, one more on the dash and run a 3 slot USB adaptor in my 12V cigarette lighter port) for years. I am soon adding a Midland MTX575 that will run out to an auxiliary power tray. In future trips it is likely I will be charging a Raddiodity

$29 GM-30 GMRS Radio Handheld 5W Long Range Two Way Radio for Adults, GMRS Repeater Capable, with NOAA Scanning & Receiving, Display SYNC, for Off Road Overlanding Family Use, 1 Pack

GM-30 GMRS handheld radio through a USB port.

These are things that might be on all the time.

I will also have a winch, front bumper light bar, maybe a roof rack with rock lights. I could even see myself adding something like a Dometic fridge (or something like it). A separate HAM radio will likely go in.

How much is too much for the ole Alternator? Is there any accepted conventional wisdom on this?

And what do you do when you reach that limit? Put in a bigger alternator? Put in solar (as the owner of a bunch of portable solar generators I have to confess that I am a little skeptical of this)?

Thanks.

 

You could use math and figure it out pretty easily but there is overhead through the battery if it's intermittent use. Example: a loaded up winch uses far more watts than the alternator can put out but it still works. The alternator just has to recharge the battery, it's not carrying the electrical load by itself.

 

OK, probably stupid question, but can you give a simple math example?

 

My alternator light came on once on a Sonoma I had on the way home, I didn't have an extinguisher so I called my wife and told her to have the water hose ready, this was after she put water on it.



The belt got so hot it melted the tensioner.



And the belt was as hard as a rock.




The front bearing went out is what caused the fire.







This is the balls out of the bearing.

 

So, taking a first stab at this, my USB-C devices all charge at up to 3 amps (so 4X3=12 amps), the Midland MTX 575 is 15 amps, so a total of 27 amps ... I assume that is safe?

 

Yikes. Were you drawing heavily on it with devices?

 

No, something had been making a little noise for a couple months but I couldn't figure out what it was. It was obviously the bearing going bad

 

Alternator fires are not solely caused by electrical overloading. They are caused by mechanical failure. Electrically, an alternator is protected with fuses. As mentioned above, the battery is the load side of an alternator.

 

Holy crap. I used to own an old access cab Sonoma 2WD….Was such a piece of garbage hahaha

 

Bearings are great ill they run dry of grease, then its heat and next fire.
The plastic and foam in a vehicle averages 600-900 lbs. That is what makes the fire spread, plastic is not a good in a mechanical world.

Good thing you had a water line at hand, this was a minute away from a total loss,..

 

This is not the total load on the alternator. The truck itself is drawing a load.

However I don't think you're anywhere near rated capacity.

 

So ... did you get your alternator core charge credit?

(Awesome meltdown and photos)

 

This thread is all too coincidental. Bought a used car last week and the alternator + battery took a dump on the first day of ownership. That battery light is not a good light!

 

Scrap pile it went

 

I was 2 miles from home when I started smelling smoke. I knew if I stopped it was over.

 

Depending on your insurance coverage, you could have made that your lucky day. I kid, I kid, I'm a kidder. But still...

 

Watt's law & ohms law can be used. You can find power/resistance, voltage or current if you know 2 of the 3.

Amps x Volts = Watts (Watt's law)

So if your device draws 5 amps at 12v, that's 60 watts.

Had written up a whole paragraph with examples but it never posted and now it's only showing the one example above. The gist is that things like the starter and a winch draw far more power than the alternator can provide. The alternators job is to charge the battery, the battery can provide huge amounts of power for short periods of time and the alternator charges it back up when the load drops.

 

OK, thank you. Refining the question, is there some limit (eg watts) I need to stay within?

 

Technically, yes. That number is something huge, though. A healthy battery should be able to provide 600+ amps for 15+ seconds without damage. 600 amps x 12 volts = 7.2 K watts (7200 watts). The real consideration when adding things to the electrical system is if the circuit it is being added to is up for the task. Example: if you add a dash cam to an existing 10 amp circuit, you would probably be fine since dash cams typically draw milliamps (less than 12 watts). So even if the circuit already has a 5 amp load on it from the factory for something like interior lights, adding the additional small load won't overload the factory wiring or the factory circuit protection device (usually a fuse). But if you add a huge light bar that pulls 15 amps and you put it on a 20 amp circuit with a 15 amp load from the factory, like heated mirrors or something, then turning on the light bar will overload the circuit and the fuse will blow. The circuits are protected by fuses rated for the wiring, so swapping the fuse for a larger one will allow the light bar to work, for a little while at least, until it overheats the wiring, melts insulation, possibly causing a fire, etc. What I'm getting at is whatever you add to the electrical system, make sure the circuit you put it on is suitable for the added load. For things that have more than an amp or so draw I always recommend running a new circuit from the battery/distribution block with wiring and fuses/breaker sized appropriately for the device and the load it will put on the system, or finding a factory circuit that is unused for an option that's not equipped. When doing the latter, you still have to consider the existing wiring size and calculate if it's suitable for the load that will be added to it. And empty fuse block slot with 32AWG wiring to it isn't going to be a good choice for something that draws 20 amps at 12v, no matter what size fuse is put in that empty spot. Also, fuses/breakers or any circuit protection devices should be as close as possible to the voltage source so that the amount of unprotected wiring is minimal.

 

So for the usb-c chargers, that’s likely at the output, which is 5v (assuming they aren’t usb pd here) which would be 15 watts, or a little over an amp at the input.


And your radio is only going to pull that much power when transmitting, if even then, fuse ratings are going to be a little larger than the expected max load of the device.