How do our alternators charge our batteries

[Saltdog]

I have a 2001 T-28 with a bank four six volt batteries (for the house), and one additional starting battery.

Do you know if when I run the boat does the alternator charge both banks of batteries if I have the battery switch on all. And only bank one of two if I switch to 1 or 2?

Also I keep the batteries charged with my inverter when plugged into shore power (that is supposed to be better for the batteries) How do I know if both banks are being charged?


Thanks for your help

TS

[RicM]

I think your question should be phrased "How does MY alternator charge My batteries?". There is very little consistancy in the stock systems in Albin boats, and your boat which is 10 years old and has been through how many owners(?) has probably been modified at least once because I have never heard of that configuration coming from the factory. The way it SHOULD be set up is that the alternator and the shore power charing system is connected to both battery banks when charging, but the battery switch (off,1,2 & both) will draw only from the bank the selector is set to when powering the boats 12V systems. That said, the only way to be sure is to buy yourself a digital multi-meter and go exploring.

[DougSea]

Hi TS,

Follow this post: viewtopic.php?f=7&t=864&hilit=charging+relay

for a start. There's some good information there, along with suggestions on how to see what you have.

After you read that -

IF your battery banks are simply wired to a single battery switch then you should probably NOT run in the "both" position. This is because your two banks are made up of very different battery types. (I'm assumning they are both Lead-Acid batteries but big golf cart batteries and a typical start battery are NOT going to follow the same charging needs).

"Both" should only be used if the starting battery has a problem and can't start the engine.

Let's assume your start battery is #1. To start the boat put the switch in the number 1 position, and just leave it there. There is no need to switch to #2 while you're running. You haven't impacted your house bank at all.

You arrive in a nice little cove and anchor. You shut down the engine. You should soon switch to bank #2 only and run your radio, tv, lights, whatever....

The next morning you want to get underway. Switch to battery #1 and start. Run for 10-20 minutes (you probably need less) to top off your start battery. Now switch to #2 (not both) and charge up your house bank. Note - your house bank is probably pretty much discharged and will want a lot of charging current. If you had the switch on "both" your start battery would most likely start discharging into your house bank. At the very least the regulator will read a charge state somewhere in between what's actually happening with your batteries and NEITHER will get the correct charge!

Hope that makes sense! Fire away with any additional questions!

[Saltdog]

Doug, thanks for the link. It was helpful.

I am still not sure that I understand how I am currently charging. Your example of switching to the starting battery to start & just leaving it there makes sense. Can you change the switch while the engine is running?

I use a heart interface (inverter) to charge my batteries when I am on shore power. Where should the switch be for that? Do you think if I had my switch to house that the inverter would only charge the house, and vice versa?

Also which battery do the bilge pumps use, or do they use both? I would like to think that my inverter would keep the battery that is powering the pumps charged if a leak developed.

It seems kind of complicated.

TS

[DougSea]

Doug, thanks for the link. It was helpful.

I am still not sure that I understand how I am currently charging. Your example of switching to the starting battery to start & just leaving it there makes sense. Can you change the switch while the engine is running?

I use a heart interface (inverter) to charge my batteries when I am on shore power. Where should the switch be for that? Do you think if I had my switch to house that the inverter would only charge the house, and vice versa?

Also which battery do the bilge pumps use, or do they use both? I would like to think that my inverter would keep the battery that is powering the pumps charged if a leak developed.

It seems kind of complicated.

TS

So, some more assumptions...

I would guess that since your inverter is also your charger that the position of your battery switch determines which battery is being charged. Again, because your batteries are different you should probably NOT switch to both for the same reasons I give above while charging from your engine.

I don't know where your bilge pump pulls power except that it is PROBABLY connected directly to one of the battery banks. Or, if not directly, then to a busbar which is wired straight to one of the banks - the battery switch should not impact this. Look for a set of smaller red wires, along with the big cable that runs to your switch, connected to one of the batteries. This would be your "constant on" DC feed. Your stereo "memory circuit" wire would go to this as well.

And yes, you can switch the battery while the engine is running, just never to the OFF position.

[Carl]

I would guess that since your inverter is also your charger that the position of your battery switch determines which battery is being charged. Again, because your batteries are different you should probably NOT switch to both for the same reasons I give above while charging from your engine.

I do not believe the inverter/charger cares what position your battery switch is in including off. If you are plugged into shore power and in the charge mode it will charge your batteries regardless of battery switch position. It charges through the same cables directly to your batteries which it uses for the inverting process. If the charger has a second bank charging circuit, this goes directly to the start battery. You may have a second battery switch between the battery bank and the inverter, this one will need to be in the on position for it to work in either the invert or charge mode.
Hope this helps.

[DougSea]

I would guess that since your inverter is also your charger that the position of your battery switch determines which battery is being charged. Again, because your batteries are different you should probably NOT switch to both for the same reasons I give above while charging from your engine.

I do not believe the inverter/charger cares what position your battery switch is in including off. If you are plugged into shore power and in the charge mode it will charge your batteries regardless of battery switch position. It charges through the same cables directly to your batteries which it uses for the inverting process. If the charger has a second bank charging circuit, this goes directly to the start battery. You may have a second battery switch between the battery bank and the inverter, this one will need to be in the on position for it to work in either the invert or charge mode.
Hope this helps.

Well, in the case of my 28 my post was connect. As you point out an inverter/charger uses the same cables for charging as it does for inverting. And those are the big honking 1/0 cables that are either wired to A battery bank or, more likely, to a switch. at the very least you would want a single position switch to be able to fully de-energize the inverter. Mine had no supplemental charging feed.

So TS - both Carl and I may well be correct. Boats are wired in as many ways as there are installers...ok, maybe not that many, but a lot!

It's fairly easy to test what your setup is with a bit of following where wires go, a simple multimeter, and some time.

Where are you located? Perhaps an AOGer can help out.

[Denis]

Just a side note, I was always told to never change the battery selector switch with the engine running, that doing so would harm the internal circuitry in the alternator. Instead, wait until the engine is shut off then make your battery bank selection. Is this not true? Denis

[loubennett]

Battery switches are make-before-break. That means when you switch from one position to another the new connection is made before the old one is broken. Consequently when switching from one battery to the other there is always a battery connected. The only problem is switching to OFF. When no battery is connected and the engine is running bad things can happen to the alternator/regulator. I think it's because the alternator can lose it's field current but maybe someone else can explain that better. The same problem can occur with your car if you were to disconnect the battery with the engine running, but usually no one is tempted to do that.