Ideal voltage for 12 V system, particularly with a mix of DC motors and other loads

Question

Is there a distinct advantage to higher or lower voltage in a 12 V system?

In other words, is it better to run the system at one end or the other of the voltage tolerance: 10.8 V vs 15 V?

I specifically ask because I have both 24 V and 12 V systems on my boat. The 12 V systems consist of mostly lights, navigation equipment like GPS and VHF radio and water pumps. I achieve the 12 V system voltage by way of a DC-DC converter adjustable from 10-15 V. I have had it set to 14.5 V so far, as most of my equipment state they can tolerate a wide range in voltage. However, I was setting it high as it makes my water pumps run faster, which, in the case of my freshwater maker, yields faster fresh water output.

The drawback is that some of my cheap LEDs were failing. But they are not important and their wellbeing is not worth much in the big picture.

This makes me wonder if the slight increase in water production is a false economy if the rest of the system is less efficient at this voltage - for example, the LEDs.

I’m sure it is a wildly-complicated subject but, broadly, what voltage should I set things to? My primary goal is longevity and efficiency.

Answer 1

Power consumed for most of the loads you describe will be given by \$ P = \frac {V^2} R \$ so increasing voltage by, for example, 10% from 12 V to 13.2 V will cause the power consumed to increase to 1.1² = 1.21 times the 12 V value. This will raise the operating temperature and a standard rule of thumb is that the expected life of the devices will halve for every 10°C.

Most devices designed for automotive use will probably be OK at 14 V as that's the typical alternator output when the engine speed is, say, at double idling speed.

Devices with switched mode power-supplies (SMPS) will accomodate a range of input voltages and output a stable specified voltage.

So, I'm afraid, it's up to you!

Answer 2

The alternator on a running motor will often keep the voltage at 14 or even 14.5. I think that is a reasonable voltage. Probably you can save a bit of power by going at lower voltages. Pumps in general will use less total energy when they deliver their liquid at lower pressure. (I mean kWh per gallon will be less). But it shouldn't be a big difference over the range we are talking about. To save your LED's, maybe you could drop down to 13.8V which, as people have commented, is kind of the "nominal" value for many 12V system components. Also, your marine VHF radio may not transmit at full power at lower voltages. I would feel comfortable going down to 13V, but ultimately it is your decision.

Answer 3

Most automotive (and by induction, marine) equipment made for 12v is actually optimized for the float voltage of 12v lead-acid battery. It is like 13.8v . That's what headlight bulbs, radios, etc... are rated for.

Then again, in a 12v system one can never be sure how much exactly a particular piece gets - wire voltage drops are significant.

Most electronics, otoh, are either very low power to care for and/or powered by a switching-mode power supply units that are almost equally efficient over the whole 10-15v range. This includes the better part of LED lights (I just came accross some lights that are 9-35V rated). Running these at higher voltage makes them more efficient by getting lower voltage drop over the cable.

p.s. having some experience with a motorhome I can advice you to get as much equipment as possible running on 24V. DC-DC converters are usually quite a hassle.