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Old 31-10-2017, 23:23   #1
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Understanding battery use

I just purchased my first sailboat a Cal 34. I have been sailing for years I have a good general knowledge of most of the boats systems I am still learning the specifics and I have some questions about battery usage.

I am living aboard and on the boat most of the day. I am plugged into shore power and have had the battery bank on to use refrigeration and other electronics. I have a large battery bank with four 12 volt batteries. The AC panel does not have all the electronics on it so that is why I have been usin the batteries. The battery charger is hooked to the AC panel .

When simply plugged into shore power, am I charging the batteries? Do I need to run the battery charger to charge the batteries?
When I tried to charge battery while using it, my AC switch “popped” off on its own. Is this a safety feature? Is it possible to run the battery charger while the battery is on and in use?
How long should I plan to run electronics off of the batteries before they need a charge?

Any advice or tips would be helpful, thanks!
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Old 01-11-2017, 05:06   #2
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Re: Understanding battery use

Quote:
Originally Posted by DASailor View Post
When simply plugged into shore power, am I charging the batteries?
Depends on your setup, but usually the answer would be yes.

Quote:
Originally Posted by DASailor View Post
Do I need to run the battery charger to charge the batteries?
Unless you have some alternative way of charging them, yes.

Quote:
Originally Posted by DASailor View Post
When I tried to charge battery while using it, my AC switch “popped” off on its own. Is this a safety feature?
More likely a wiring problem.

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Originally Posted by DASailor View Post
Is it possible to run the battery charger while the battery is on and in use?
For any ordinary marine battery charger, yes. Of course, not knowing just what you have, or how it is wired, there is always the possibility that in your particular case the answer is no.

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How long should I plan to run electronics off of the batteries before they need a charge?
That depends entirely on the capacity of your batteries and the draw of your electronics. You are going to have to figure that out for yourself.

Good luck.
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Old 01-11-2017, 05:32   #3
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Re: Understanding battery use

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Originally Posted by DASailor View Post
When simply plugged into shore power, am I charging the batteries? Do I need to run the battery charger to charge the batteries?

When I tried to charge battery while using it, my AC switch “popped” off on its own. Is this a safety feature? Is it possible to run the battery charger while the battery is on and in use?

How long should I plan to run electronics off of the batteries before they need a charge?
Generally: yes (assuming you have the charger turned on), yes, that's not good, the "switch" (breaker) itself is the safety feature, yes, and it depends.

Usually you don't want to run your batteries down to less than 50% state of charge (SOC)/50% depth of discharge (DoD).

How old is the charger? What model, size, etc.? Has it only just begun tripping the breaker? (Could also be a breaker that's gone bad.)

-Chris
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Old 01-11-2017, 05:46   #4
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Re: Understanding battery use

When you have your battery charger turned on, not only are you charging the batteries but the charger provides all of your 12v needs. In other words, the batteries aren't being depleted, and then recharged by the charger. My Mastervolt charger for example, can run the 12v loads without a battery being connected to the system.

If your batteries are low and you turn on the charger it will be pumping maximum capacity into them. To do this, it will be using maximum AC amps. If you also have a number of AC loads running you might be asking too much of your system causing the breaker to pop. Try turning everything off first and then just turn on the charger just to charge the batteries.
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Old 01-11-2017, 06:04   #5
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Re: Understanding battery use

I want to try to explain a little bit the electric functions for you.

Electric current flows from the "source" to the "drain" - per definition from Plus (+) to the Minus Pole (-).

The potential difference is called Voltage - if you look to a water pipe between two water tanks it would equal to the height difference between the two tanks. the higher the one is in relation to the other, the higher will be the pressure on the pipe. Same for electrics. More Voltage equals more tension, more pressure.


Now to batteries and chargers. they act exactly as interconnected tanks. The one (Battery Bank) has reached a voltage of 13.8V (hight 1) and the charger delivers 13.8V (height 2), so the tension / Voltage between the two is Zero, no current will flow. This is the case when the battery bank is full and the charger is in "trickle mode" to keep the battery full.

If you add another pipe and drain the system through it the Water of both tanks will go down. Same with electric. When you turn on some serious load on 12V the Voltage will drop a little - let say to 12.6V. There will be a current flowing trough the load. Because this also leads to a Voltage difference between the charger and the battery, in the same time the charger will provide a current to re-charge the missing Voltage, as long as the charger current abilities are higher than the power you draw, the charger will deliver all electricity to the load and the battery will stay full.

As in real world, - if your drain pipe to the load is larger (high current) then the charging pipe of the charger (lower load current), part of the content of the tank (Batteries) will go through this paths and will slowly empty the tank (Battery). As soon you switch off the load, the battery will be re-charged to full, because the charger will continue to deliver a current until there is no more difference in the Voltage between charger and battery.

Your circuit breaker have nothing to do with this. They only blow / switch off - if there is a over-current or a fault (short cut) in their circuit. In normal operation this should not occur at all.

To indicate how full your battery is, you need to know what the voltage is and what current is flowing to / from the battery. This can be done by a battery monitor device, that counts continuous all current and measures the voltage, so it can calculate the state of charge of the battery.

So the answer to your question: YES, you can run a charger and draw current from the battery at the same time. It is done always, when you run the engine (Alternator charges the batteries while in use), when you have other sources of power on loading the batteries (Solar panel, wind generator, power generator...) etc. it is normal to do so. When you drive your car, the engine / alternator constantly tops up your starter battery and provides current for the ignition, lights and all other electrical circuitry in your car, when the engine is off, everything runs on battery only.
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Old 15-11-2017, 08:12   #6
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Re: Understanding battery use

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....Now to batteries and chargers. they act exactly as interconnected tanks. The one (Battery Bank) has reached a voltage of 13.8V (hight 1) and the charger delivers 13.8V (height 2), so the tension / Voltage between the two is Zero, no current will flow......
The water tank analogy is a good one but your explanation is I'm afraid very confusing. When a charger is connected to a battery they are both immediately at the same voltage (height of water) because they are connect by a pipe with almost no resistance. 13.8v in float mode can still be delivering a lot of amps into a battery that is not yet fully charged.

A much more accurate explanation is needed, and you have to consider how the batteries charge and discharge their energy. To understand this you have to expand the water tank analogy.

So imagine that within the tank (battery) there are many many smaller tanks (thick battery plates) and each of the smaller tanks are connected internally by small pipes. When a charging voltage (head of water) is applied the first internal tank (battery plate) fills first (surface charge), so the charger and the battery are at the same voltage. Water slowly percolates through the small pipes to the other smaller tanks (deeper into the plates) so the charge current keeps flowing until all the small tanks within the main tank (battery) are fully charged. This is why a charger gets to the absorption voltage 14.4-14.8v and needs to stay there for several hours to fully charge a battery.

This also helps to explain why when a battery is discharged quickly its voltage immediately falls (the first small tank) and when the discharge stops the voltage rises as the surface charge (first small tank) is filled from the inner tanks (deeper plates).
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Old 15-11-2017, 12:30   #7
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Re: Understanding battery use

"When I tried to charge battery while using it, my AC switch “popped” off on its own. Is this a safety feature?"
Let's say you have a 30-amp shore power connection and matching AC breakers. And you have a nominal 15-amp AC load on the boat. That leaves 15 amps available to do other things, like run the battery charger. 15 amps at 110 volts is about 117 amps at 14 volts, so there should be enough "extra" AC to power the battery charger even when the batteries are very depleted and the battery is sucking full power from it.
I don't see any obvious reason why the AC breaker should pop, unless you are using close to 30 amps from the AC lines, leaving much less for the charger, in which case a heavily depleted battery pulling a full load from the charger would cause the breaker to pop "sometimes" but not when the batteries were already at a higher charge state and pulling a lower load. That's a variable you'd need to look into.

One of the basic boat electrical books (Charlie Wing, or Sherman) and a good multimeter are invaluable in clearing up electrical problems in short order. Couple of days to read the book, a lifetime of baffling questions solved.
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Old 16-11-2017, 08:23   #8
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Re: Understanding battery use

There are two reason to pop an automatic breaker, both are related to high current.

There are pure thermal, pure inductive and thermal/inductive breakers.

The thermal breaker just heats up and breaks the line in case you overload the wire near or slightly above the breaker capacity for a long time. It helps to keep the circuit closed on short time - higher loads e.g. when a electric motor starts, so it allows a short time higher current.

The inductive breaker is mainly there to block quickly very high currents, that appear when you or a faulty device produces a shortcut on the line. The high current induces a strong magnetic field, that releases the pre-loaded spring and cuts the circuit in a very short time - before any cable gets hot.

Well and there are also safety devices / breakers that measure differential currents of both wires, and if the in-going current does not match the outgoing, the breaker considers a leakage to ground/earth somewhere and breaks both lines to safe your life from electric shocks.
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Old 16-11-2017, 09:44   #9
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Re: Understanding battery use

Try charging with the electric heater turned off.
Your in Seattle I bet you are running a portable electric heater. ( I am )
if you can't get it figured out pm me.
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