Without getting into all the technicality of different variables, math, etc.... Can someone explain how it affects the amperage/current?

Say I have a battery 12v 10Ah rated at 10hr discharge.

1. If I put a step down to 6v, will it still be discharge in 10hr?
2. What If I have a step up to 24v, will 10Ah now be 5Ah and will be discharge in 5hrs?
3. What happens to the current? Can I still pull 1amp from it?

 

All things come down to power. Power can be computed as the product of voltage and current. For any conversion scheme that you come up with, the following statement will be true: "Power out will always be less than power in; sometimes it will be much less." go back and answer your own questions with that thought in mind. As a rule of thumb you can treat all conversions as being 80% efficient. This assumption will at least get you in the ballpark.

Oh you want me to do an example. OK. Your 12V battery will deliver 10A for 10 hours with a discharged voltage of 10.8V or more. In practice you don't want to discharge your batteries all the way, and as the input voltage drops the DC-DC converter has to work harder. That is let us say 120 Watts for 10 hours or 1200 Watt hours. Now apply a DC-DC converter that is 80% efficient. At 6V you can get 16 A, for 96 watts for 10 hours or 960 Watt hours. If the 6V load draws less than 16 A, then the 12V battery will last longer. Say it draws 4 A, so 6V times 4A is 24 watts, and 24 watts will expend 960 watt hours in 40 hours. Whatever the battery does, for whatever length of time it does it; it still runs out of juice at the same level of power drawn. So the answer to the first question is; it depends on the load at the output of the converter.

 

Hi Papabravo. Thank you for the very detailed explanation! Insightful!

So in short, the step up in voltage does not affect the battery's AMPHour life at all, it all depends on how much the Load is pulling?
If this is the case, then why would people combine two 12v battery together instead of just getting a stepup to 24v?

 

If you step the voltage up to twice the battery voltage, the battery will have to deliver twice the current that the load draws. For example:

battery 12V
load 24V 2A

The battery will have to deliver 4A. This is with perfect efficiency. At a more typical 80% efficiency it will have to deliver 5A.

You calculate how long the battery will last by the current drawn from the battery, not the current delivered to the load.

bob

 

Hi Papabravo. Thank you for the very detailed explanation! Insightful!

So in short, the step up in voltage does not affect the battery's AMPHour life at all, it all depends on how much the Load is pulling?
If this is the case, then why would people combine two 12v battery together instead of just getting a stepup to 24v?

The short answer is because you can't get something for nothing. The cost in these case is the losses due to inefficiency.
BTW -- the same principle applies to any mechanical system with friction, from a hand pump to Don Prudhomme's classic 1962 digger.
https://en.wikipedia.org/wiki/Don_Prudhomme

 

Ah. Thanks for the information guys! This really helped me out.