Less than 12

Gunni · Jan 14, 2016

"Oh, how did I let it get to this, a dead battery? I could have logged off SailboatOwners.com and shut down the laptop last night, but no! Now the batteries are dead" Well, time to pull on the shorts, get up on deck and hoist the main! Honey, we'll be sailing off anchor and cruising into the Abaco Sea just like we did in the old days! Hand me my work gloves, I'll be sweating the rode. No, no worries, the solar panels will have the batteries charged by nightfall under this Bahamian sun! Here is my handheld GPS, hand me the charts up on deck. I'll need the handheld VHF radio. See if you can make that iPad thingy get a fix. Let the adventure begin!"

Stu Jackson · Jan 14, 2016

You switch to the reserve bank.

Gunni · Jan 14, 2016

Stu Jackson said:
You switch to the reserve bank.

Stu! Where is the excitement and adventure in that?

Stu Jackson · Jan 14, 2016

Gunni said:
Stu! Where is the excitement and adventure in that?

I do like your answer better.

Interestingly enough, it's pretty much what I do on a regular basis.

Handheld instruments used in lieu of fixed base stuff, no windlass, and sails. Occasionally sail on &/or off the anchor just to keep the skill set alive.

Paper charts abound. Like many on this and other boating forums, I love looking at charts and maps.

Sumner · Jan 14, 2016

If it was desperate that I needed to move or get the engine started I'd put them in series. I use to have a large tractor that was 6 volt and started it on a 12 volt battery all of the time. The amps actually will go down and it will spin faster. The above was only my experience so you make the decision knowing that it might not be the best thing to do.

A good example that even if you don't have solar mounted that having a 60-100 watt panel onboard with a charge controller that could be connected to the batteries if something like this happened might be some pretty cheap insurance. Also I carry one of the battery packs made for starting and do have a separate start battery (per Stu's advice),

Sumner
============================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...
Mac Trips to Utah, Idaho, Canada, Florida, Bahamas

Johnb · Jan 14, 2016

Perhaps a good reason to
a) be able to rig your dinghy motor onto the stern of the mother ship
b) have a dinghy motor with charging capability
c) maintain a good 12 volt system

CharlzO · Jan 14, 2016

Only thing I can think that might get interesting, is if you're running an alternator... you rewire to series to get it started, so that's good. but if you take the belt off the alternator, you aren't charging your batteries up that are still low. So if you leave it on? Now you're wired funky, and I imagine you would want to rewire them back asap, and now you have incoming voltage along the way. That, and while I know you probably COULD get away with it if you're down that low in voltage, and hopefully would have enough amperage to crank over and get it started, I personally wouldn't feel comfortable doing that. Much better to have a reserve bank or backup plan to start with.

Joe A · Jan 15, 2016

I would never, ever wire two 12V batteries in series (unless in a 24 V system of course). I'd find some other way. That's just me.

kloudie1 · Jan 15, 2016

Solution to getting belt back on:

I am not advocating this.. just saying.

Sumner · Jan 15, 2016

If I had to do this, and I don't ever see this situation happening to me or 99% of the boaters out there here is what I'd do. Leave the Alternator and all the rest of the system wired to the pos/neg posts of only one of the batteries that are in series, the second one in series. Then run the positive, main starter feed wire only to the positive pole of the first battery in series.
Once the engine is started the one battery (12 volt part of the system -- second in series) will be charged and the rest of the 12 volt system should operate normally. Once that battery is charged then put things back the way they were and the second battery will be re-charged.

Again this is only if you have no other alternatives and if you don't understand the above I would not do it (I could post a schematic)

Sumner
=======================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...
Mac Trips to Utah, Idaho, Canada, Florida, Bahamas

Stu Jackson · Jan 15, 2016

Johnb said:
c) maintain a good 12 volt system

Right answer.

Geez, what's so hard?

Over the years we keep hearing people say: I don't need a reserve bank, I'll just swap out wires when stuff goes south. How incredibly stupid. Set up a robust and working electrical system, and instead of swapping wires when an emergency strikes and you're not really in a position to swap wires, just turn the blinkin' switch.

Sure, sometimes batteries go south, but unless you have AGMs (another reason to not "need" them), if you monitor your system and understand how it works, nothing will happen instantaneously. And 12V batteries can be sourced almost anywhere, even six V batteries (as frequently discussed on cruisersforum, where skippers travel a LOT further than most of us on this forum).

Maine Sail · Jan 15, 2016

Any reasonably sized house bank should EASILY start your marine engine even with batteries as low as 11V. Course we all know our house batteries should never dip below 12.0V - 12.1V even under your average house load.....

If you really murdered them simply switch to the OTHER BANK, that we all should have...

woodster · Jan 15, 2016

Stu Jackson said:
Sure, sometimes batteries go south, but unless you have AGMs (another reason to not "need" them),

What am I missing here about the AGM's

walt · Jan 15, 2016

Here is technical approximation to the original question.. If you model a battery as a voltage source in series with an impedance (resistance), and assume both batteries are identical, and you only consider that the start up torque of a DC electric motor is proportional to current..

If each battery impedance is much less than the DC motor winding impedance, the series batteries produce twice the current - and twice the torque. This case is somewhat obvious and would be the normal case for a good set of batteries

If the each battery impedance has degraded and now is the same as the DC motor winding impedance, each case results in the same current into the battery - and the same start up torque

Now.. if the impedance of each battery is much higher than the DC motor impedance, then the parallel batteries would produce twice the current - and twice the start up torque.

When your batteries are fairly shot.. you are more likely in the region of the second and third cases and for this simple model, you would be better off leaving the batteries in parallel.

Stu Jackson · Jan 15, 2016

woodster said:
What am I missing here about the AGM's

Besides Maine Sail's numerous posts about them?

They can fail catastrophically (i.e., without warning) compared to wet cells.

Here's some of my favorite Maine Sail AGM Top Ten Hits: i.e., why they ain't the right battery for normal recreational boaters, or at least folks who don't know electrical systems and how to design, install and manage them, which, to me, is over 80% of the people I know in person and on these forums, given the questions asked and answered)

AGM Battery Issues (from Maine Sail)
http://forums.sbo.sailboatowners.com/showthread.php?t=124973

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
http://forums.catalina.sailboatowners.com/showthread.php?p=848465&highlight=darn agm

druid · Jan 15, 2016

If your batteries are that low, it means they're basically discharged and have very little charge available. Hooking them in series would not help that situation: you need CURRENT (yes, Mr. Ohm says you'd get more current with higher voltage, but the terminal voltage of the batteries would drop to nothing due to internal resistance).

Having said that, I HAVE found myself in that situation a few times. Solutions if you're already there:
- Use the decompression lever if you have one
- Have a solar panel or other means of charging: doesn't have to be big, just turn off all the loads and wait.
- As JohnB said, rig up the dinghy's engine
- Sail
- Tow the boat with the dinghy - I've done it rowing the dinghy.
- If it's only a little ways to a source of AC, paddle!

Of course, the best solution is to not get there in the first place, which means mainly keeping your starting battery ONLY for starting, and ensuring it's up to the task.

druid

Anonymous 121765 · Jan 15, 2016

All,

I'm getting into this thread alittle late but, I can tell a simple plan I use to not drop below 12V.
Aside of a failing battery or some draw in the system, I like to sail in daylight & anchor at night.

I plan my arrivals beforehand & plan motoring up some channel or some distance to the anchorage. If no channel, I run my engine a minimum 1/2 hr. beforehand to my anchoring spot. This charges your batteries for nighttime use.

I always make it a point to judge time & distance for motoring when possible. I do this motoring beforehand to recover the power lost during the day's sail. This now charges up my 2 batteries.

If using alot of power while @ anchor, sometimes I run the engine at night before I turn in if running things on batteries. And, the first thing I do when I awake is to start my engine & let it run for 30 minutes while I drink my coffee & then after, I can restart my engine & I motor out thus charging the batteries for the day's use.

Of course, this only works with healthy batteries & a sound electrical system. This however, depends on you DC health status. I have used this method for over 20 years & have never had a starting problem.

Be aware of your 12VDC while anchored pal. Keep in mind that It's easy to run your engine before retiring at nite depending on what your elec. draw was & have a planned routine to use.

CR

Nick · Jan 15, 2016

On our Hunter we have all LED lights so low drain on house batteries... the only item we can say runs all night is our stereo... We sometimes just run the Iphone into bluetooth speakers but both are self contained (battery) till we plug them in for a charge. Agree with CaptnRon and that is about how we keep our batteries maintained... We keep 4 batteries on the boat... one each for engine and house use with selector switch, and the other two batteries for our 'appliance' use with inverter... they are separately charged from the house/engine bank... they could be used for either by rewiring if needed for emergency use.
Both banks are monitored and only addition is to add more solar but so far not needed till more cruising time takes us away from marinas.