Electrical Musings

[DotDun]

Originally Posted by s/v Jedi

Related: standard alternators can kill batteries if motoring for long periods, as their internal regulators output 14V all the time.

Lesson: if you're motorsailing or motoring for a long period, pull the field wire (blue) from the alternator.

Cars have done this forever. Not arguing, just saying.....

[Dockhead]

Originally Posted by s/v Jedi

There were four Lifeline Gel batteries in parallel. It's one bank for both engine and genset. Engine is just a 4-cyl. Yanmar so nothing special.

The idea behind it must have come from a tech that worked for the previous owner. I have no clue why they did this.

Now I have the two Odysseys and there is a 1-2-both-off switch there so that I can isolate a bad battery. I can also switch house batteries to the starters if needed.

Related: standard alternators can kill batteries if motoring for long periods, as their internal regulators output 14V all the time.

Lesson: if you're motorsailing or motoring for a long period, pull the field wire (blue) from the alternator.

cheers,
Nick.

I keep engine and genset batts separate. I keep a pair of jumper cables in the battery box which houses them, but your 1-2-both switch is more elegant. Unlike you I can't use the house bank for starting, because it's 24v.

[goboatingnow]

By the folks the smart gauge article on paralleling batteries by keeping the lengths the same etc is pure junk science. It true in an abstract theory. In real life the extra resistance of a foot or two of high power copper cable is negligible compared to connector resistance terminal resistance and variations in battery discharged equivalent series resistance. In a typical bank the actual lengths have no effect. The batteries all shoulder the load more or less equally ( check the SoC if you don't beleive me)

Dave

[Dockhead]

Originally Posted by goboatingnow

By the folks the smart gauge article on paralleling batteries by keeping the lengths the same etc is pure junk science. It true in an abstract theory. In real life the extra resistance of a foot or two of high power copper cable is negligible compared to connector resistance terminal resistance and variations in battery discharged equivalent series resistance. In a typical bank the actual lengths have no effect. The batteries all shoulder the load more or less equally ( check the SoC if you don't beleive me)

Dave

Thank you - I had a hunch that this is so, but as a certified electroignoramus, I thought I would keep my ears open and mouth shut.

Doesn't the charge even out anyway? Don't momentary imbalances get made up automatically? I do know that if you jump a dead battery, charge will from the good to the dead battery, tending to equalize the charge between them. Isn't this the same?

[goboatingnow]

Originally Posted by Dockhead

Thank you - I had a hunch that this is so, but as a certified electroignoramus, I thought I would keep my ears open and mouth shut.

Doesn't the charge even out anyway? Don't momentary imbalances get made up automatically? I do know that if you jump a dead battery, charge will from the good to the dead battery, tending to equalize the charge between them. Isn't this the same?

The nature of the charge curve means that for example connecting a 80 % charged battery to a 60% one does not result in two 70% batteries. Hence the general precaution to parallel banks of similar capacities and charge them all up so they are equal
Dave

[Maine Sail]

Originally Posted by goboatingnow

By the folks the smart gauge article on paralleling batteries by keeping the lengths the same etc is pure junk science. It true in an abstract theory. In real life the extra resistance of a foot or two of high power copper cable is negligible compared to connector resistance terminal resistance and variations in battery discharged equivalent series resistance. In a typical bank the actual lengths have no effect. The batteries all shoulder the load more or less equally ( check the SoC if you don't beleive me)

Dave

Funny I was just on the phone with the engineering department at Enersys just this morning for some odd issues I have been noticing with some Odyssey batteries.. These issues are unrelated to bank wiring. Enersys are the folks who invented the Spiral AGM and who also invented the thin plate pure lead technology batteries now sold under the Odyssey label. They insist that end connecting their batteries will be problematic and the batteries will become out of balance. Their words, not mine...

I specifically asked this question after you and Andina called the practice of wiring parallel batteries, as the manufacturers recommend and show in their drawings, "junk science" or something similar..

When I consistently see readings from my Midtronics and Argus analyzers tell me that batteries do get out of balance at a significantly higher rate, and earlier in life, when end connected, and considerably less so when cross connected at opposite sides of the bank I have to really question whether or not it is junk science?

I think for now I will continue to wire as Enersys, Trojan, Lifeline and other manufacturers recommend and also listen to what my battery analyzers are showing me.

Enersys strongly recommends connecting the positive to one end of a parallel bank and the neg to the opposite end. They told me they will be placing stronger language on the site in regards to what they consider proper wiring of parallel batteries in the future. They update their technical manual fairly regularly and recently added Peukert numbers to the latest update.

I will be speaking with the lead engineer later this week so will try not to forget to get even more clarification on this point.

[s/v Jedi]

This was years ago and I really can't remember my readings, but I too measured imbalance during charge and discharge. But that might still not lead to any further problems because as one battery delivers more power, it gets discharged more which makes the next one take over the lead etc.

But I didn't want any of that so wired my 3 parallel strings each with it's own, equal length, jumpers to bus-bars... the method that most title as madness



cheers,
Nick.

[goboatingnow]

I was specifically mentioning the concept that it is neccessary to have equal lengths of battery interconnect. Connecting the battery bank as oddesy suggest is good practice.

[Maine Sail]

Originally Posted by goboatingnow

I was specifically mentioning the concept that it is neccessary to have equal lengths of battery interconnect. Connecting the battery bank as oddesy suggest is good practice.

Then we're on the same page. Perhaps I misunderstood your post in the other thread. Sorry if I did...

[chala]

Originally Posted by Maine Sail

And cross connected like this:

I do see measurable reason to wire per the second diagram in this post but can't effectively comment on Smart Gauge Method #3 because I have never seen any boat wired like that .....

Battery…………..Links on +……….. Links on -………..total links.
…1…………......………..0……………………3………….......…..= 3
…2……………......……..1……………………2……….......……..= 3
…3……………......……..2……………………1……….......……..= 3
…4………………......…..3……………………0……….........…..= 3
Each battery as the same amount of links may be Smart Gauge needs to explain the mathematics. Now I wonder about Smart Gauge algorithms.

[Dockhead]

Originally Posted by chala

Battery…………..Links on +……….. Links on -………..total links.
…1…………......………..0……………………3………….......…..= 3
…2……………......……..1……………………2……….......……..= 3
…3……………......……..2……………………1……….......……..= 3
…4………………......…..3……………………0……….........…..= 3
Each battery as the same amount of links may be Smart Gauge needs to explain the mathematics. Now I wonder about Smart Gauge algorithms.

I think they mean THROUGH how many links is each battery connected to the loads. The point being that according to this method every battery has the same number of links between it and the load.

My batteries are wired like that, at least, each group of four is.

I have two groups of four batteries, and those two are quite far apart. But charge imbalance is one problem which I have not observed.

[chala]

Originally Posted by ebaugh

I just faced this problem with designing a 48 cell lithium array 12 cells in parallel, then 4 in series. I'm still not sure I have it right, so I keep reading.

Have you read that one?
Cell Balancing and Battery Equalisation

[chala]

Originally Posted by Dockhead

I think they mean THROUGH how many links is each battery connected to the loads.

An equal 3 in each case.

[chala]

Originally Posted by s/v Jedi

Ah, but now we're discussing on how to correctly connect batteries in parallel. The previous discussion was about parallel connection being inefficient, Nick.

And unsafe.

[noelex 77]

Originally Posted by chala

And unsafe.

Most crusing boats have battery banks consisting of batteries wired in parallel. So you better elaborate on your safety concerns.