50 volt - higher-voltage electrical systems

[mlts22]

I don't see how it would make batteries unbalanced, especially two 12 volt jars in series. The alternative is an inverter to go to 120 volts, then rectify it back to 12 volts, which will have a power loss (~20%), while a buck DC-DC converter would just put out clean 12 volt current with far less circuitry needed, and less electricity lost as heat.

[cruising7388]

Originally Posted by avanti

The pitting is caused by arcing, which happens when a voltage exceeds the breakdown voltage of air. It really has little to do with load. That is why you can get a long spark touching a doorknob in the winter--lots of volts but negligible current. If the voltage is low, it doesn't matter how much current there is--unless you exceed the breakdown voltage, there will be no arc.

Sure, in the final analysis, arcing is the result of sufficient voltage to ionize the space between separating contacts, but I disagree with your conclusion that the load level is never a component involved in the duration of contact arcing. I think its more complicated than that.

Yes, if the load is purely resistive, the voltage across the separating contacts is determined by source voltage

However, I think an inductive load like a motor changes that equation because at the moment of contact separation, the collapsing voltage in the motor winding generates a pulse across the switching contacts and the level of that pulse is a function of the operating current level of the inductive load.

The easiest place to observe this is by watching the contacts of an RV transfer switch subjected to varying loads during the switching sequence. If the transfer occurs during little or load there is little or no arcing during contact separation. But if a load like an AC compressor is present during transfer the arcing is substantial and repeated events like this is the likely cause of contact welding experienced in transfer switches.

So, I agree that arcing is ultimately a function of voltage present at the separating contacts but I think that the level of inductive loads fed by those contacts will affect the voltage level found at the separating contacts and consequently, the duration of the arcing.

[booster]

Originally Posted by mlts22

I don't see how it would make batteries unbalanced, especially two 12 volt jars in series. The alternative is an inverter to go to 120 volts, then rectify it back to 12 volts, which will have a power loss (~20%), while a buck DC-DC converter would just put out clean 12 volt current with far less circuitry needed, and less electricity lost as heat.

It wouldn't unbalance the way you have described it. The Roattrek system center tapped the 24v bank in the middle to get 12v so the 12v ran on 1/2 the batteries only and unbalanced the discharge. With a 24-12v charger, you would not have an issue.

[GeorgeRa]

On older cars, before times of electronic ignition, points were used to generate high voltage on sparkplug electrodess. Contact pitting was common those days.

Remember those weekends for points replacement, right gap, dwell, new capacitors, life was good, but it is still good without the pesky points.


Seems like ages ago -

https://www.youtube.com/watch?v=W94iksaQwUo

[cruising7388]

Originally Posted by GeorgeRa

On older cars, before times of electronic ignition, points were used to generate high voltage on sparkplug electrodess. Contact pitting was common those days.

Remember those weekends for points replacement, right gap, dwell, new capacitors, life was good, but it is still good without the pesky points.]

It's a tribute to this classic design that these points can open and close many millions of times before requiring renewal. The condenser, aka capacitor, absorbs the the pulse produced at the coil winding when the points open.

[avanti]

Originally Posted by cruising7388

It's a tribute to this classic design that these points can open and close many millions of times before requiring renewal. The condenser, aka capacitor, absorbs the the pulse produced at the coil winding when the points open.

Yes. The issue with points is a good example of the problem. Last time automakers looked at higher voltages, the engineers were starting to think that they might have to add a big old capacitor on every switch. They eventually thought the better of the whole enterprise. As I said, techniques such as solid-state relays and multiplexed wiring have taken the issue off the table.

One way to think of how capacitors help is to observe that by constantly charging and discharging in sync with the points, the cap essentially turns the current across the points from DC to AC. Arcing is not generally a problem with AC, since the current reversals rapidly extinguish the nascent arcing. AC-rated switches are much easier to design than DC ones.

[Boxster1971]

Just saw attached article in June issue of SAE TRUCK & OFF-HIGHWAY ENGINEERING magazine. The product base for 48 volt automotive system is growing.

[BBQ]

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Yes, especially with the new "Mild-Hybrid" engines. They have a high voltage generator/starter combo unit that runs off 50v.