Another Battery Question... Help!

Dora~Jean · Posted: Sat Mar 11, 2006 12:05 am Post subject:

Mike,

Not sure where you read the engine mfr's would not approve of each engine being directly connected to their own battery. My local Yamaha dealer said it was fine, but then again, they didn't know as much about their engines than I did...hmmm. Maybe it depends on engine make/model for their susceptability to switching glitches. My Perko battery switch is definitely a make-before-break type as most all are. That's essential to make sure the engine charging systems ALWAYS see a load. But I did install a 50 (or 100?) amp fuse in series with each engine connection to prevent an electrical fire in the event of a short.

Raining cats and dogs here now (Simi).

Steve

Sea Wolf · Posted: Sat Mar 11, 2006 5:10 am Post subject:

The problem with using batteries in parallel is that a strong one will discharge through the weak one, since it it putting out more electrical pressure, or voltage, or is in a higher state of charge, which is all the same thing.

This means that if you connect a fully charged battery with one that is discharged, a current will flow from the charged battery into the discharged one. The amount of curent or amperage flow depends on the voltage difference between the batteries.

A smaller difference and all that hapens is you have a moderate current flow and wind up with two batteries with their voltage readings and storage capacity averaged out as they seek equilibrium.

But as the condition of the two batteries gets greater, bad things can happen. The current flow can be so great as to cause the electrolyte in the weak battery to boil and explode in extreme cases.

Another problem occurs when one of the batteries has an internal condition which results in its self-discharge. In this case, paralleling the batteries will drain the good one right down into the condition of the self-discharged one.

So there's ample reason right here not to be connecting batteries in parallel, let alone the ones that center on keeping one battery in a fully charged state to start the engine(s).

Because of these reasons, we come up with the general rule for most applications to not use the batteries in parllel unless necessary.

However, it is possible to parallel two or more batteries if they are in the same age, general condition, and state of charge. If you are very sure that your two, three, or four or more batteries are of very equal condition and thus can avoid the pitfalls above, they can be connected in parallel to supply great amounts of amperage and/or simply to keep their states of charge equal. And they can also be charged as one big battery in this same simple way. Parallel usage and charging is much simpler than engaging in the constant switching batteries on and off as they are used, and then facing the same problem when trying to charge them equally.

To practice this, start out with all new batteries of the same make, capacity, etc., and monitor their independent voltage periodically to see that they are still in equal condition. When one starts to show variation, replace it immediately. If they are near the end of their expected life, replace them all. I'm currently doing this with four group 27 deep cycle marine batteries and have had no problems doing it over the years with first two, then four batteries.

Joe.

Dora~Jean · Posted: Sat Mar 11, 2006 10:41 am Post subject:

Joe,

Thanks for the reminder on paralleling batteries and "their condition". Common thinking when hooking up and using batteries in various applications is that they're NEW -- what could go wrong? I think we've all been there and experienced a premature battery failure or some other anomoly that comes along (Murphy comes to mind..). I'd rather not buy 2 batteries is one goes killing the good one, or worse, to see my CD go up in flames -- hmmm, bad picture... Paralleling is for short-duration, emergency stuff if you don't have isolators. BTW, any voltage imbalance between parallelled batteries is quickly transferred, limited only by the internal resistance of each battery (2 ft, 2-4AWG cables are VERY LOW resistance)!

That's it. I'm going out TODAY and spring for another $6 trickle charger at Harbor Freight so I can 'independently' maintain my batteries 'without' paralleling them. It'll double the current going into them, but hey, 2x0.01 amps ain't all that much!

Steve

dogon dory · Posted: Sat Mar 11, 2006 11:38 am Post subject:

Sorry, Folks - Post Deleted By Author

Sea Wolf · Posted: Sat Mar 11, 2006 11:40 am Post subject:

Steve-

Thanks for the refinement of ideas regarding the paralleling of batteries and the caveat about paralleling!

Those who practice frequent and or long term paralleling of batteries definitely do run the risk of one of the batteries going bad and causing one of the problems mentioned.

The odds on having a problem are somewhere between those in Russian Roulette and those on winning the PowerBall Lottery, but where exactly I'm not sure. Determining those odds would take some investigation we would probably find they would depend a lot on the quality of care and supervision given the batteries.

Joe.

Sea Wolf · Posted: Sat Mar 11, 2006 11:45 am Post subject:

Dan-

Thoughtful and very true points on battery use! We all learn and sharpen our ideas from these discussions. Thanks for the ideas and additions! Joe.

CAVU · Posted: Sat Mar 11, 2006 12:45 pm Post subject:

A lot of good points about batteries and switch positions. A point of caution for us with twin engines. The use of "both" position on the battery switch is much different with twins.

wailedcentipede · Posted: Sat Mar 11, 2006 8:03 pm Post subject:

years back having fried a new battery first trip out i than did a library thing if i read it right:

a regular battery will die if it is drawn lower than 10.3 new or other wise. it may still lite things up but when you hit the starter cross your fingers . first nite out i let the fridge run it down it was toast after that. the numbers may not be right on but a 12 volt battery runs between 10.3 and 12.7

battery's sitting for long periods ?? the plate's coat over this also shortens the life .. coats over with what?? can't remember but it's in the book. i think the trickle charge cure's this

another thing is my battery charger will show the green lite my little float in the tube thingy floats in the green, lites, spot lite every thing lites up but hit the starter which needs apox 200 amps its fried despite the OK readings

i think a separate starter battery and a separate house battery is a must. murphys law, things will catch up on you. i always switch off the starter battery when under way. have the three way switch

the last i read on deep cycle batters they can be drawn down 4-5 times but they also will fold if drained completely ... like a fridge running away no battery alarm ..

i'm into intergraded navigation items etc. but i think a starter battery should be on its own, separate from any other electrical thingy

Dora~Jean · Posted: Sat Mar 11, 2006 8:44 pm Post subject:

I learned a few things about batteries when I bought my first Link 10 monitor. It's really a small computer that tracks and integrates current usage over time to calculate how much 'capacity' (amp-hrs) you've used. My batteries are combo deep/starting rated at 110 amp-hrs. According to the Link 10 literature, you can draw down a battery to a maximum of 50% of it's capacity. I shoot for about 70% maximum down just to add a little buffer.

For example, if you burn your 1 amp anchor light for 12 hrs overnight (actually the C-Dory standard (Perko) bulb draws slightly less), it will consume 12 amp-hrs. The % capacity remaining is then (110-12)/110 = .89 or 89%. If you also ran your stereo (assume 1 amp), 2 interior lights (1 amp each) and your Wallas heater (assume 1 amp) for 4 hrs before going to bed, that would be (1+2+1)*4 = 16 amp-hrs more used. % capacity remaining would be (110-12-16)/110 = .74 or 74%. The Link 10 does all this calculating in real time. Add a refrigerator, inverter, microwave, etc, well, better get more batteries to boost your capacity (amp-hrs).

All this is fine, good and accurate when the batteries are 'new'. The Link 10 doesn't take into account reduced capacity as the battery ages. But you can plug in a lower 'capacity' number say after 2 yrs to approximate that.

Notice the battery voltage doesn't come into play, just the current! There are more complex interactions that must be accounted for to accurately calculate capacity remaining, the Link 10 does that too. The faster you pull current out, the more rapid your capacity reduces (non-linear). Likewise when recharging, you have to put more back into the battery to bring back to the same charged capacity (Perkert's Law pronounced "Purr-cay" or "Purr-care" I forget).

Now I forgot the point I was trying to make other than voltage alone is not a good indicator of condition, depends on surface charge accumulation, temperature and several other factors. Lesson over, sorry if got carried away...

Steve

Sea Wolf · Posted: Sat Mar 11, 2006 10:02 pm Post subject:

Batteries, electrical circuits, electronic devices, appliances, and the like are indeed complex topics with many facets and facts.

Read as much as you can and as often as you can. Some people find the topic more interesting and understandable than others.

No one will comprehend everything they read the first time through. The more you learn over a period of time, the more you gradually understand and can utilize in working on your boat.

Knowledge and skill in this subject is just like any other aspect of boating and seamanship: competency develops over a period of time with experience and shared knowledge.

You won't become an electrical engineer or a master mariner overnight, but patience and diligence will go a long way towards helping you become a better boat owner and skipper through the years.

Joe.

Dora~Jean · Posted: Sun Mar 12, 2006 2:00 am Post subject:

Thanks Joe, I like your approach much better, keep it simple...

Many times I have people ask me about my Link 10's and how they work. Well of course being an electrical kind of guy I start to go into the details -- that's about when I see their eyes glaze over and want to move on. Bad habit of mine, but good if you want some quiet time... Disgust

Steve

Dreamer · Posted: Sun Mar 12, 2006 3:38 pm Post subject:

My boat electrical Guru has a solution for keeping batteries charged while idle. If put away charged, an AGM (absorbed glass mat) battery will lose just tenths of a volt over several months! As in all things for boats, you pay dearly for this advantage. I'll save my battery system plan until it's installed and tested. It seems so logical on paper... We'll see. Roger
Dreamer

Sealife · Posted: Sun Mar 12, 2006 7:21 pm Post subject:

Was able to run the charger for several hours yesterday, after an abortive start. Hooked up the shore power cord to my new $35 adapter and extension cord, turned on the charger, but failed to notice that you first have to turn on the main breaker. Duh! So, came back to the boat after a couple of hours to check on the charge......no change. Discovered my error, ran it again for several hours, and lo and behold, it's now showing 12.5 volts, about 3/4 full. Also confirmed that the port engine is connected to the house deep cycle battery, and the starboard to the starting battery. All the electronics are routed through a breaker switch, then to the house battery. Supposedly then, with the engines off, both switches still on, all house current would come from the house battery. If that's so, then why did I get identical low readings on both batteries?

Here's the mfg wiring diagram for these switches. Note, it is only for a single engine; our factory is adapting it for twins. Question is, does it defeat any of the switches features to use it for twins? One thng the factory does differently than what Bep advises, is they hooked the battery charger leads directly to the batteries, rather than through the switch, but I don't see that as a problem.

http://www.bepmarine.com/PDF/INST_716SQ_100A.pdf

Not For Hire · Posted: Mon Apr 03, 2006 10:33 am Post subject:

Flapbreaker wrote:
>>>Sealife I have the same BEP switch setup on a Single engine (boat new in august). I recently had a problem that I didn't expect. Launched the boat and when I went to start the motor I got nothing. Not even an ignition light. I was and still am puzzled as to how there wasn't enough juice to start the main since the VSR (voltage sensitive relay) is supposed to isolate the two batteries to prevent this. Lucky for me I have a trolling motor wired to the house battery so I pull started it and let it run for a couple minutes. Then I tried the main and it worked. Needless to say I'm still confused about this BEP setup and just what the heck it's doing for me even after reading the details on their website.<<<
Have you figured out what went on here? I understand the the VSR devices made by BEP will charge the second battery only when the first battery is charged to or receiving a charge of 13.7 volts or something like that. So the theory is that the first battery would always be charged even if you ran the second battery (the house battery) down. Of course, this is more complicated in three battery setups with one or two engines. Interested in your comments.

Regards

Sealife · Posted: Mon Apr 03, 2006 2:31 pm Post subject:

Mark,

No, I haven't figured anything more than what I stated in my previous post. Since recharging my batteries, they now seem to hold their charge, so I'm baffled as to what happened, and still have questions about the setup. I queried Bep by e-mail, and have gotten no response.