ELECTRICAL SYSTEMS I : A Great Diagram from Blue Sea

[bob mitchell]

I have been working continuously (in my head) on a brand new electrical system for my Newporter. Five owners with their own supperimposed ideas without removal of previous owners wiring, as well as just antiquated wiring and systems, created an overwhelming disaster potential. Furthermore, while I don't begrudge anyone their standard of living in terms of energy consumption, I do know myself well enough to realize that I, primitive that I am, prefer robust simple systems as opposed to trying to squeeze every last efficiency and comfort out of really sophisticated systems that I cannot personnally master and maintain, or afford.
At any rate, I diagrammed my system repeatedly as I read Calder (Boat Owner's Mechanical and Electrical Manual) and did months of internet research. It is a challenge.
Basically I kept realizing that I did not quite understand this or that, would hit the research again, and review available products, until i was comfortable, and then I would do a new diagram.
Well, on one of those stop and rework trips - about hooking up an ammeter to get the reading I wanted, or, in other words, knowing what the ammeter was reading depending on where it was located, I found this great GENERAL ELECTRICAL SYSTEM DIAGRAM -THE ONE I HAD BEEN LOOKING FOR SO LONG!!!!!!! when I googled "Blue Sea Ammeter Installation.

And lo and behold it was so close to mine, and I was so relieved. The diagram reinforced the idea that when LOADS, CHARGING DEVICES, and BATTERIES are in a circuit the CURRENT CAN FLOW EITHER WAY!!!!! They left some of the details off, like the ignition circuit, but that was just fine for clarity's sake. So as I went through the available ammeters I saw 1)direct read ammeters (like on my Newporter) where a heavy wire goes to and from the ammeter and all the current goes through the meter (which adds a lot of path length to the heavy wire circuit and sticks heavy loads and wiring up in my instrument dash) 2)Hall effect ammeters, which involve electromagntic deflection of electrons, but don't appear particularly accurate over a wide range of temperatures (do your own research on that one) 3) Shunt Resister ammeters that insert a low resistance precision shunt resister into the main circuit (see diagram)and then have two thin sensor wires that measure the voltage drop accross the resistor. These two thin sensor wires run to the ammeter where the voltage drop is interpreted as current flow.

Current = Voltage Drop / known resistance

The SHUNT RESISTOR AMMETERS can be analogue ($30 to $80)or digital. ($167 for Blue Sea, including shunt, $98 for paneltronics, not sure if shunt included , if you shop around).
The thing about digital is because they use op amps that were designed for around 5volts "common mode voltage" the shunt has to be inserted near the negative battery terminal, unless you buy the $65 shunt shifter as well, and then you can put the shunt near the postive terminal. I AM NOT TRYING TO EXPLAIN ALL THIS CRAP, JUST KIND OF SHARING WHAT TO LOOK OUT FOR!!! DON"T REALLY KNOW WHAT I AM TALKING ABOUT! (If you are interested in op amps and their use in metering circuits og to www.masteringelectronicsdesign.com and then read the sections on Differential Amplifiers. You may not do all the math but the general ideas will give you a good sense about what is going on in digital meters.)
On the other hand, the Analogue ammeter's shunt can be inserted at either end. I decided that for my outside console instrument panel I just basically wanted to know if my batteries were discharging or charging, so going back to an earlier point that IN A CIRCUIT WITH LOADS,CHARGERS,AND BATTERIES THE CURRENT CAN FLOW BOTH WAYS DEPENDING ON THE LOAD DEMAND, I picked a point right between the PERKO "ALL" and my main postive bus (location 2 on diagram), which meant I would measure all current (load and charge) except for my starter. This meant that I included the huge windless current which was rated at 150 amps, even though it probably would never draw that, so I chose a Stewart Warner +/- 150 amp (284AD @ $51.85 with shunt 413717@ $45.09) ordered from "Service Express", a master distributor for Stewart Warner in Omaha, Nebraska (402 331 1797). The meter is a typical 2 1/16" circle dial for dash. The best thing is that when you install a shunt virtually all the current goes through the shunt, so if the shunt is marginally rated it heats up and distorts the reading as well as wastes energy, as well as might be potentially dangerous. The shunt that this 150 amp ammeter uses is also the same shunt that their 300 amp ammeter uses, so I know I am way below the current limits.
When you install a "ZERO CENTER AMMETER" it allows you to read rate of current discharge as well as charge, i.e. the net positive or negative flow, the difference between the load current and the charge current, one being negative and one positive depending on how you hook it up.
As I mentioned before, I tend to avoid high tech black boxes that do everything for you because 1) I can't afford them, and 2) when they break you are screwed.
An example of how your own brain might use the data from a "zero center ammeter" is the fact that

Energy Consumed = rate of energy usage (power) x time
= voltage x current x time (P=V x I)
= volts x amps x seconds
The units can get a little confusing - in physics the units would be Watts=joules/sec
(power=work/time)
or since work and energy are essentially the same thing joules = watts x time
(energy= power x time)
BUT in batteries we commonly talk about the amount of energy stored in terms of AMPHOURS, where we assume a voltage of the standard 12 volts, and leave the volts out.
(basterdazation of units)
Anyway, lets just say you started your engine, and your alternator is putting out 70 amps, which is going to recharge the battery (from the energy drain to start the engine). Assuming that there is no other electrical load your ammeter should read 70 amps. But then you start winching up the anchor and it draws 90 amps. In location 2 the ammeter should now read negative 20 amps, so you are now in a net discharge mode (using energy stored in the battery, as well as that being produced by the alternator). If the windless runs for 1/10 of an hour drawing 20 amps of current (from the battery, because the alternator is producing the other 70amps needed, if the engine is running) then you have consumed 2 amphours of your battery's stored energy, which is a relatively small amount for a 100 amp hour battery. If the engine wasn't running you would have consumed 9 amphours (about 10% of your stored 100 amphours) of your battery's stored energy. This example is a simplification with fictitious values - there are a lot of variables that enter into the real world - but I would say the calculations are fundamentally applicable.
So there's a little about what I have been up to. Should have photo and diagrams soon. (by the way, ammeter does not read current for perko isolation switch bypassers like bilge pump, and in my system, solar.)

[Clyde A. Phillips]

Bob,

Good write-up. I found this a little above my head, but I’ve been in deep water before. You have laid out a good answer about dc circuits and ammeter use. The Blue Sea System (bluesea.com) has a lot of .pdf files of instructions that are easy to download and save, and they have tons of information about setting up dc circuits correctly. Though I will probably never need this info, it is a good study, and you have set me on a new adventure.

Thanks,

Clyde