Charge Computer with engine on or off?

[RBEmerson]

One more voice in the chorus of "bigger isn't better". Honest, you'll get more benfit from what have with the simple change in the regulator instead of spending for the extra batteries. If you can't charge them properly (not enough alternator to do the job), they'll give out sooner.

Bobsadler, scout places like auto supply stores or JC Whitney for plug-in battery "analyzers" (voltmeters, usually with LED's) or wire up a short pigtail, on a power point plug, with something (maybe an SAE trailer hitch connector) you can tag with a DVM and not have loose wires waiting to short out.

[Cowboy Sailer]

Mark, O.K. I will use little words! Your alternator is capable of putting out more than your batteries can accept for more than a few minutes. It is best to run your fridge and charge your computer while your engine is running. It really is O.K. to measure voltage at the outlet that you are now using. Don't mix new batteries and old batteries. Enjoy youself and don't stress.

[Jim Cate]

Originally Posted by RBEmerson

it is.

Measure the battery voltage at the batteries (unless you want to wire up a set of test terminals with the proper heavy wire).

Actually, if all the terminals are used for is checking the voltage at the batteries, small, even tiny wires are ok, 'cause the DVM draws essentially zero current, and so voltage drop in the wires to the terminals is also essentially zero.

We use shielded "twisted pair" in such applications to reduce noise pickup... it's cheap, small and readily available.

Cheers,

Jim and Ann s/v Insatiable II lying Gladstone Qld Oz

[Ex-Calif]

Originally Posted by bobsadler

dan: what's the simple indicator you have plugged into the cigarette lighter outlet

thanks

Originally Posted by RBEmerson

Bobsadler, scout places like auto supply stores or JC Whitney for plug-in battery "analyzers" (voltmeters, usually with LED's) or wire up a short pigtail, on a power point plug, with something (maybe an SAE trailer hitch connector) you can tag with a DVM and not have loose wires waiting to short out.

Bob - RBEmserson is right.

I would love to have a xantrax, solar to assist my alternator etc, etc. But something like this is what I have. We find it useful as we really use the engine for 2 minutes getting off the mooring and getting the sails up and again picking up the mooring. Often we sail off ond on so we don't even run the engine.

However we run fans, electronics and so forth all day. When the voltage gets low we know it's time for an engine run.

[swagman]

Hi Mark,
You've already got lots of good advice but to step back to a simple premise, I was always taughts to fire up any device that needs power WHEN our engine was running and unplug etc when engine goes off.
On all our long passages the moment we fire up the engine to recharge our main batteries, we also swtich on our 12v watermaker, plug in the laptop, rechargable batteries, rechargable torches, turn the fridge and freezer up to v. cold, etc etc.
Always worked for us.
JOHN

[MarkJ]

Originally Posted by swagman

On all our long passages the moment we fire up the engine to recharge our main batteries, we also swtich on our 12v watermaker, plug in the laptop, rechargable batteries, rechargable torches, turn the fridge and freezer up to v. cold, etc etc.
Always worked for us.
JOHN

Thanks for answering the question, John!

I am still digesting everyone elses advice. I should be committed to the looney bin shortly

Mark

[bobsadler]

regrettably in Azerbaijan there is a bit of a shortage of "JCWhitneys"

i was hoping to track one down on-line but googling hasn't produced much - anyone have a brand name?

[RBEmerson]

Er, JCWhitney has a website. Try this spiffy meter when you're back in Bermuda. LINK

[RBEmerson]

Originally Posted by Ex-Calif

[...]However we run fans, electronics and so forth all day. When the voltage gets low we know it's time for an engine run.[...]

Er, not the best scheme. In general a battery is considered discharged when 50% of its capacity has been expended (that is, pull 100 AH out of a 200 AH bank, and you've hit 50%). Past that, you start to do Bad Things to the plates, etc. Bottom line: going until the lights dim means you're hammering the batteries, and that means shorter battery life [...and] replacing batteries sooner than necessary. Not Good, eh?

Unfortunately, [putting] a voltmeter into the mix doesn't tell the full story. With all the loads on, the true state of charge, based on voltage, will be lower than it really is (could be worse - at least a voltmeter doesn't make things look better than they are). OTOH, it does give some cushion; when you hit 12.4-12.5VDC, time to think about charging the batteries.

[Captn_Black]

Originally Posted by Hud3

Mark,

I have Lifeline AGMs, and have had some chats with the tech guy at their headquarters. Among other tidbits, he told me that a battery bank should be made up of batteries of the same size and type, and the same age. Don't mix 'em up, or their lifespan will be shortened. Also, for AGMs, the charging voltages are critical. You really need a smart, three-stage charger, or you will shorten the lifespan of your bank. Until you can afford the smart charger, I'd hold off increasing the size of your bank.

Thats useful to know... so if I were to add a 3rd battery I should charge it separately perhaps?

[Ex-Calif]

Originally Posted by bobsadler

regrettably in Azerbaijan there is a bit of a shortage of "JCWhitneys"

i was hoping to track one down on-line but googling hasn't produced much - anyone have a brand name?

The one I posted is for sale on Amazon for about $15.00.

Amazon.com: Equus 3721 Battery and Charging System Monitor: Automotive

[Ex-Calif]

Originally Posted by RBEmerson

Er, not the best scheme. In general a battery is considered discharged when 50% of its capacity has been expended (that is, pull 100 AH out of a 200 AH bank, and you've hit 50%). Past that, you start to do Bad Things to the plates, etc. Bottom line: going until the lights dim means you're hammering the batteries, and that means shorter battery life [...and] replacing batteries sooner than necessary. Not Good, eh?

Unfortunately, [putting] a voltmeter into the mix doesn't tell the full story. With all the loads on, the true state of charge, based on voltage, will be lower than it really is (could be worse - at least a voltmeter doesn't make things look better than they are). OTOH, it does give some cushion; when you hit 12.4-12.5VDC, time to think about charging the batteries.

I think what you post is consistent with the advice I gave. I don't run my batteries until the lights dim. I run until the green LED is off and the yellow is starting to flicker off.

At that point the bus voltage is around 12.6v

[hellosailor]

Mark, are you sure you have AGM batteries and not older gel cells? Gel cells typically needed lower voltage, that's why I ask.

But with any conventional battery--AGM or wet--the output of the alternator should typically be around 14.3-14.4 volts when the system is running and powering devices (like the fridge and computer) and actively charging the batteries. If you are seeing 13.2-13.6, it means either you have a bad internal regulator in the alternator (they usually are replaced, not adjusted) or your alternator was mismatched (and is turning way way too slowly to put out a real charge), or you have bad connections, or corroded cables, or just too many meters of thin wiring. Or, in some cases, they have tied the "charge sense" lead from the alternator back to itself the wrong way.

No matter how you look at it, something is wrong. It probably is preventing your batteries from taking a full charge, and also quite possibly doubling the amount of engine time versus what you really need to charge the batteries. Big waste of $$.

Cigarette lighter sockets are notorious for being connected with long runs of thin wire (causing a voltage drop) and having corrosion in them (same problem) so they aren't the ideal place to test voltage. Using a real meter at the battery terminals is more reliable--but the lighter gizmo certainly is handy, once and IF you verify it is reading the same thing as battery terminal voltage, or you take note of the difference.

[bobsadler]

dan: thanks