Drawing from battery while at dock

[dmksails]

What affect does using 12VDC power have on the batteries while at the dock and connected to a battery charger?

Right now only the cabin lights are using 12V power for only a few hours each night. I'm considering adding a wifi router to 12VDC power and this would be on 24-7 unless I turn it off.

[Sailmonkey]

If you’ve got a battery charger on and it’s in float, unless it’s horribly undersized your batteries are not providing current to your loads.

[Lepke]

ditto. I live aboard and I run many 12 volt items. Especially some hydronic heating controls and blower motors. My Dyno 8d batteries seem to last 8-10 years.

[Teknishn]

I liveaboard and am swinging on the hook about 80% of the time. When dockside I don't connect to shore power. My 200-watts of solar panels takes care of everything that I need. 2 House banks of size 24 deep cycle batteries and a 2500-watt inverter. Cloudy days may be a bit close on usage if I run the inverter too long (that and the laptops are power hogs).

Haven't connect to shore power in about 9-months I think. Solar or a wind-gen might be worth looking into in your case.

[john61ct]

As long as the loads are drawing less current than the charger provides, the bank is not cycled at all.

And if it does get drawn a little bit, shallow DoD%, that will not have a significant hit on its longevity curve.

[Shrew]

If the battery charger can push more amps than your systems are pulling, then you should be fine.

[US1Fountain]

I have a Pronautics 1240 charger and 1 of the listing features is it also works as ‘Dock side’ power source. I assume this means exactly as to what you are referring to.

[John_Trusty]

Easy version -- things that do not heat or move mechanically use very little power (watts). Take a look at your proposed load (any 5 volt transformer will do), and you'll see that it draws almost no power (probably less than 1 amp). Your inverter probably loses more in heat than the load you are drawing. Your battery charger can absorb this small load without drawing on the battery at all.

[ZULU40]

Thats exactly how my boats supply operates

2 separate battery systems selectable via rotary switch
Engine battery is a flooded cell with 1000 CCA
And the house are 3 AGMs

A 20AH xantrex truecharge 3 bank charger supplies all the batteries as per their individual requirements.

The 12v systems are made active by the rotary switch as Off-1-2-1&2, but the charger has access to the batteries all the time we are shore power connected.

There is also a dual socket 240v outlet principally used for tools for working on the boat. But the boat and everything on it are 12v including the hot pressure water. All of the shore power was a really dangerous set up so it was stripped out and replaced with wire in conduit to an IP67 RCD circuit breaker with just two runs also in conduit, one to the charger and the other to the dual outlet.

[TrentePieds]

Your battery charger will have a "read-out" that gives the number of amperes the charger is putting out. For understanding what has been said above, try this:

Turn off EVERYTHING you can so noting other than the batteries takes current from the charger. Say the read-out now sez "1.5". That means that the batteries are now consuming 1.5 amps of current for charging purposes, i.e the batteries are storing that quantity of power away for future use.

Now turn on the dome light over your dinette. The read-out might jump to "2.8" or so. That means that the dome light is consuming (2.8 - 1.5)A = 1.3A. The current put out by the charger simply "splits" so the batteries continue to take what they need, and the rest is accounted for by the "house loads".

Now turn on, say, the bilge pump. The read-out might jump to "7.9". The batteries are still consuming 1.5A and the light 1.3A for a total of 2.8A. The pump is therefore consuming (7.9 - 2.8)A = 5.1A.

Now turn off the dome light and the read-out will drop to (7.9 - 1.3)A = 6.6A, being 1.5A for the batteries plus 5.1A for the pump.

It's that simple. Just go play with it until the pattern becomes clear to you.

For these simplistic purposes you can envisage current flowing through a wire, measured in amperes, as analogous to the volume of water flowing through a pipe measured in gallons per minute. Current splits where there is a "junction" in the wiring, just like water splits where there is a "TEE" in the piping.

TP

[ramblinrod]

Originally Posted by dmksails

What affect does using 12VDC power have on the batteries while at the dock and connected to a battery charger?

Right now only the cabin lights are using 12V power for only a few hours each night. I'm considering adding a wifi router to 12VDC power and this would be on 24-7 unless I turn it off.

None, if the total current drawn (by loads and batteries) is less than the charger can put out.

[US1Fountain]

For clarification, as I'm not sure I understand with certainty

Say you have a 10A draw while plugged into shorepower and the 40A charger is in float stage. Is the charger providing the 10A and batteries 0A, or are the batteries providing the 10A and the charger is simple replenishing the batteries? If the readout on the charger shows its putting out 10A, how do we know where that 10A is going, to the batteries or to the load?

[mitiempo]

Originally Posted by US1Fountain

For clarification, as I'm not sure I understand with certainty

Say you have a 10A draw while plugged into shorepower and the 40A charger is in float stage. Is the charger providing the 10A and batteries 0A, or are the batteries providing the 10A and the charger is simple replenishing the batteries? If the readout on the charger shows its putting out 10A, how do we know where that 10A is going, to the batteries or to the load?

If there is no current going to the batteries without a load (in other words they are fully charged) then when you turn on a 10 amp load the battery charger provides the current. The batteries are full so will not accept the current.

[john61ct]

And all the 10A is being drawn from the charger, nothing's touching the energy stored in the bank.

[US1Fountain]

Thank you