Nice article, Julian. I agree. Reading through it, we can see at a glance - once you tumble to the initial idea - (and isn't that always the truth of things....it's easy once you see it). Anyway, near as I can tell, it looks like SmartGauge's way of hooking up the batteries to balance lead resistance is also the theoretically correct way to balance the battery drain.
And even though his theory checks with my own understanding, I was surprised to see how large the difference was... in spite of his using huge, short copper wire for leads between batteries.
I mean....who really uses huge 1 3/8" diameter stranded copper wire for their battery interconnecting cables? And who consistently keeps the length to be exactly 8" each?
It's nice that he gives the constants that he uses. I also agree that even if the theory checks, the magnitude of the difference is surprisingly large. Someone should check on his figures just for a "reality check. Be easy enough to do it in a spreadsheet.
Hmmm....it occurs to me that there's a quick arithmetic check possible and the advantage is that it uses the numbers that SmartGauge is reporting. Since the unbalanced batteries in Fig 1 and the balanced drain configuration in Fig 2 requires the use of slightly more cable in Fig 2 as he drew it., then the sum of currents in Fig2 should be higher as well.
That only works because he is using a constant .02 ohms in the calculations (for each internal battery resistance).
So....by using his own numbers to check - and assuming that his wiring calcs match his sketch - the sum of the drain in Fig 2 should be MORE than the sum of Fig 1 by some small amount simply because the wires are longer.
Fig1 Sum = 35.9+26.2+20.4+17.8 = 100.3 amps
Fig2 Sum = 26.7+23.2+23.2+26.7 = 99.8 amps
Oops....Hmmm....it doesn't check!! Did I copy something wrong? No....apparently not. What's going on here?
Still, if I was putting batteries in parallel I'd wire in keeping with Fig2. Betting that's pretty much the standard for batteries in parallel.
Roger L. F-28cc
----- Original Message ----- From: Julian WebbSent: Sunday, December 29, 2013 2:49 AMSubject: Re: [Electric Boats] RE: system questionsHi
While 48 volts makes built drop less of an issue than 12 or 24 volts, it's still incredibly important especially as the current goes up.
I have a 48 built system with 24 x 220ah blocks and we serised/paralleled them up two different ways just to check and were stunned at the difference, and I'm almost ashamed to admit I've worked in the electrical industry for years BUT as the attached article says when you're used to working with 110/220 it's seldom an issue.
Armchair experts will tell you "what difference can it make", please read the attached article and remember that theory is where you should start but practice I'd where you must finish so listen to both. CheersOn 29 Dec 2013 08:24, "Sheya" <sheyagiggles@yahoo.com> wrote:
Hey Mike,Thanks for the response. I believe that since we have 8 (12V 200AH blocks) that would mean we have a total of 400AH at 48V. Would you agree thats right? We would have 2 blocks of 4 in series and those 2 blocks connected in parallel, does that make sense?Sheya and Jason
From: "mike@electricyachtssocal.com" <mike@electricyachtssocal.com>
To: electricboats@yahoogroups.com
Sent: Friday, December 27, 2013 6:45:01 AM
Subject: [Electric Boats] RE: system questions
I am surprised no one has responded to your inquiry and hope this will stimulate others. I know of at least two conversions of heavy displacement Morgan 41s by members of this group and they should have good advice for you. I believe this is the proposed system and your usage:
The motor is a continuous rated 15hp that is to say 11,200 continuous rated and likely about 12hp to the shaft. The boat is a Morgan 41 which often was supplied with a 45hp motor that likely drove at peak 30hp to the shaft.
The battery size is 200AH at 48v
You are looking to sail the boat as far as Alaska from your BC location.
This is what our computer projection says and I would encourage all vendors to share your projections for this boat.
Speed & Power
Kts-Watts
2.3-480
2.9-960
3.6-1920
4.6-3840
5.3-5760
5.8-7680
6.4-12480
6.8-17760
Hull speed 7.93
Your motor should push the boat at about 6.2kts in calm and likely about 4.5 in a mixed sea state and about 3kts against a poor sea state. The 200AH battery bank will push the boat at an 80% dod for about 22NM at 3kts and 14NM at 4kts.
Mike
Electric Yacht of Southern California
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