Paul J. Thompson
Information Technology Manager
Henry Brooks Co. (t/a Bathroom Direct)
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www.bathroomdirect.co.nz
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Just an FYI. Welding cable is not advised on a boat. Its not tinned and has very fine strands which will corrode quicker. Some of it is not resistant to diesel fuel. Diesel can literally melt the insulation away. I assume you will not have any diesel on your boat, but still.Matt FoleySunlight ConversionsPerpetual Energy, LLC201-914-0466On Wednesday, May 3, 2023 at 01:19:42 PM EDT, Myles Twete <matwete@comcast.net> wrote:First of all, you can certainly split up a pack into multiple boxes---this has been done since the first EVs were produced back in the late 1800's. I have no comment about aluminum except to be sure that's what you really want (vs, say, wood/glass/epoxy molded to the hull). With my 700ah, nom. 42v pack on www.evalbum.com/492 , I have my pack split into 4 subpacks, each of the same nom. 42v (31v to 49v Lithium Ion). Same story with Dan Pence's "Ginger" (one of the first noted E-boat conversions in recent decades and 3rd earliest or so at evalbum.com --- Dan uses the same battery modules as I use and has a row of batteries on the starboard and one on the port side. He has his mounted in a ply/glass/epoxy cavity originally built and sized for lead-acid batteries back in the late 1990's---the cavities fit these ex-THINK EV Enerdel stacks well. He and I both use 4ga wire from each 35ah stack thru fuses to common points on each side. Then larger gauge cable to connect the starboard and port packs.
Details matter. You indicate your pack will be 280ah at 48v and that the cells themselves are 280ah. Given that, your splitting of the pack results in two 280ah 24v packs in series. Size your cables based on how much current you ever expect to draw from the pack. Let's say max. 7.5kw, then we're talking about 150amps max. So sure, a gauge of 1, 1/0 or 0 probably would be fine. Make sure you have a fuse near each of your 2 half-packs.
As for BMS connections, it's not really as simple as presented by Dave. Yes, the cell connection wires are "sense" wires but they typically are also "bypass" wires---that is, they need to pass the current that your BMS card attempts to bypass cells with. And even 100ma of bypass current thru a tiny, long wire can cause millivolts of voltage drop which ruins the ability of the BMS to properly sense the voltage. On an electric lift truck application I worked on, we found that 22 ga wires were inadvertently used instead of what we spec'd which was 20ga. This difference caused cell balancing to be pretty ineffective. Separate these functions (bypass and sense) and this problem goes away, however most of the BMS boards used until recently do not separate these. Maybe yours does?
Here details really matter. Cell balancing for our under 10kw boating applications should not require more than 1-2 amps of cell bypass current. On my boat, I have 20 remote BMS cards. Each has the capability of bypassing up to 12 series cell pairs at about 100ma of current from a 35ah pair of cells. This results in about a 10mv/hour balance rate, which is plenty if your cells are not all out of whack and not daily charging and discharging the pack deeply for weeks at a time. Here use-case is important.
Your 250a Daly BMS makes me scratch my head---and the website for Daly doesn't help me understand it any better. Do you have better information on these? Why on earth do they need to handle 250amps?
Thanks.
-MT (26' The Reach Of Tide --- converted to electric in 2003)
From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of aasmith970@gmail.com
Sent: Wednesday, May 3, 2023 2:54 AM
To: electricboats@groups.io
Subject: [electricboats] Splitting 48V System Into Two Boxes?
I have a question about the feasibility of splitting up my 280 amp hour 48 V system into two aluminum battery boxes, that I will be custom making making. I am constrained on the space in my Newport 28 sailboat and it would be much easier and balance the way much better if I split the bank..
I am concerned, or the question is will the leads being longer from one system to the next, and the BMS leads being different links affect the current/reading of the BMS?? The leads going between the two boxes would be made out of double00 welding cable with properly crimped terminals while the leads going between the individual cells in the boxes will be copper busbars.
Should all the BMS leads be the exact same length or can eight of them be 2 to 3 times as long as the other eight the boxes will be about 30 inches apart?
280ah new cells from Docan
250 amp BMS Daly
Delta Q charger + 150 watts solar
7.5 KW system from Foshan Green Motor
thanks for any and all comments.
Aaron
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