Keep AB or Upgrade To D class?

Thanks Steve, impressive as usual.

And you took my simple answer and turned it into a math assignment..lol

But I completely agree that no matter if using a class AB, or a class D, if the electrical system is being taxed due to excessive current demands, that issue needs to be addressed first.

Also note upgrading just the alternator is not always nessecary..and at the same time not always enough.

Read the thread on the "big 3" if you haven't already. The wimpy factory wiring/grounding is a prime offender that needs to be addressed once you get into high power systems.

I know thats the first thing I address and it has been working for me forever.

Stevdart - Here is your formula for efficiency(E is efficiency in decimal form)

(RMS * 2) / (E * 2) = Total RMS

You can then apply ohms law to calculate amp draw.

I have a question regarding efficiency.

Can you really be that general in saying an AB is 60% efficient and a D is 80% efficient ?

While researching the topic I was lead to believe they are both fairly inefficient..but better then a class A in comparison.

Wouldn't efficiency be amplifier specific as a rating , rather then generalizing? Or is it that those specs (60% / 80%) can be applied with decent accuracy regardless?

Thanks.

Master5 - Those efficiency numbers can be used with relatively good accuracy, but they do only represent the average and are not specific to all amplifiers. Some can be better or worse depending on the manufacturer.

Thanks vinspo, Thats pretty much what I though.

But using your formula above is not really a formula for efficiency. It is used to determine the total RMS if you know the efficiency to determine if the electrical/charging system/wires are up to task.

The link I posted for the calculator does all the math for you..and then determines the total power drawn from the alternator. However, you still need to know some specifics and the rockfords give the specific info with every amp they sell.

I wonder if anyone knows a way to determine the actual efficiency of a particular amp by taking measurments ?  If so please post.

What I have been doing is simply relying on the power specs of the amp depending on the ohms load. Then once I know the length of the wire I use an IASCA wire chart to determine the wire gauge and current demand. Seems to work for me so far.

Thanks everyone for all the info

BTW..if someone does now how to determine the efficency of a specific amp I do know the formula, it's basic division at the worst. But do you think a simple watt meter used to measure power in / power out would be accurate enough or is there other factors to be taken into consideration.

Thanks again.

Ok, so with this info rather then be too concerned with the specific efficiency...is it safe to "assume" that a class AB rated at the same RMS power of a class D could draw substancially more current?

And should we take this into account when deciding on system demand and wire gauge?

Iasca tells us to assume double the rated RMS power when using the chart to determine wire ga regardless of design to be on the safe side ...but my chart may be a bit dated.

Is there anything I am missing or am I on track?