Ron
I think you will find there will be a new dimension to your sailing with electric propulsion. I certainly have. In light winds I crank the motor control just a tiny bit to eliminate any prop drag which gives a nice bump up in speed without the noise/vibration of a diesel engine. It makes for a pleasant day of light wind sailing. Then if the wind picks up it’s fun to watch the amps go from negative to positive as the the prop turns the motor into a generator and begins to charge the battery. You will have to get use to the smell of clean as you won’t have any diesel, oil and antifreeze onboard to deal with.
Thank you for the concise answer to this question. When you used the word “bus” it clarified that there was actually no problem. I had read what must have been an opinion and was really overthinking the question. I much appreciate you sharing your insight.
Very encouraging words and I hadn’t even thought of the clever use to eliminate prop drag in light air.
I’m not so sure that regen will work for my boat as I understand it is paltry under 6knts and I don’t routinely see that speed.
I think it will be pretty easy getting used to the lack of smells. This electric propulsion bolsters my commitment to clean smell along with my composting head. Now I just need a built in shower. :-}
I believe, if the batteries were lead acid, that connected to the buss as described, if the battery leads are different lengths or different gauges, then the batteries will experience different charging and discharging rates. Perhaps the lithium battery BMS can over come that issue.
Another tip when using EP. If you are heading toward a buoy, harbor entrance or a point of land and you are not sure you are going to pass it without having to make a tack. You can power up the EP just enough to allow the boat to point up to make it without tacking.
I think it sounds like cascading confusion may have created a myth which is being passed around online or something and becoming a truism.
If you are using 4/0 copper cable the resistance of the cable is 0.05 ohms per 1000 feet. So for a ten foot run you’re talking about 0.0005 ohms. Even at 208 amps of maximum draw (by a 10Kw motor) you are only dropping a tenth of a volt across that much resistance. With that and good tight, corrosion-free connections on your cables the variation in internal battery resistance (not the full internal battery resistance, but just the variation between batteries) will be greater than the resistance of the cabling. Since the battery’s internal resistance is part of the charging circuit and it varies from battery to battery, that is going to make the attachment point of the motor cables almost totally irrelevant to lead acid batteries. Yeah, one lead battery might complete it’s charge a few milliseconds before the other. But that isn’t going to matter because no two batteries are alike, so they will discharge at slightly different rates, too.
And it would be completely irrelevant to anything with a BMS. Though the internals of the BMS, like most power systems I’ve dealt with, are probably calibrated to +/- 5%; so you will even see slight actual variation from one Lithium battery to the next if you go inside and measure them.
Imagine if it were possible to bolt the battery terminals directly to each other and also use the same bolts to attach the cables to the motor, generator, or whatever supply/load you are talking about. So there would be no interconnecting cables at all, just the load cables to the motor. With proper interconnection cables, that’s essentially what you are looking at. I think neat cable layout which allows you to monitor the condition of your connections would be the thing to focus on.
And I really do urge you to at least think about getting some Kopr Shield and stuffing some into the connections before you crimp them. And beneath lugs when bolting them, etc. It is both conductive (so don’t slop it all over everything) and corrosion resistant and so it should keep your connections in good shape for a long time. It is expensive and they don’t sell small quantities, but for wiring up a new electric drive motor setup and battery bank I think it would be well worth it.
I carry jumper cables in my truck and use them more often than you might imagine. (Mine are high quality, heavy cables with strong spring clamps.) More than half of the batteries I jump have loose or corroded terminals. People who have not spent a lifetime attempting to put electrons to use do not seem to understand the importance of those connections. They are always your weak link.
***Good jumper cable story, though irrelevant to this message: We were looking for a parking spot in a full parking lot a few weeks ago and saw a guy standing next to his car. We asked if he was about to leave and he said his car wouldn’t start and he was waiting for a tow. I offered to jump him and we ended up with a good parking spot right up front and he got to cancel his tow. It’s so rare that things work out like that. ***
I’m not sure those of us who don’t live in Southern California understand how existentially important a good parking space is to those of us who do live here.
But, I definitely second both the anecdote and Brian’s main point on the benefits of corrosion-protection applications.
– Bob
Me Gusta
Nonsuch e26U #233
Sailing in Southern California waters (which requires first finding a $#@!! place to park near your dock)
Brian, your last post is interesting. It makes perfect sense to me (maybe a bad sign. The following was taken from the Q&A portion of the Support tab on Ocean Volt’s website.
"CAN THE PROPULSION BATTERY PACK BE SPLIT AND PLACE IN DIFFERENT LOCATIONS?
We recommend keeping the battery bank together and in once place. This way, they can be better balanced (electronically) which makes the batteries perform better and last longer."
Are they talking about a different issue or propagating the myth?
I don’t know the answer to your question. As a generality I don’t see how it could be true. But I don’t know what kind of “electronic” balancing they are talking about. They seem to try and ship an out-of-the-box solution, so it might simply be an issue of the wiring harness that they include. The lithium batteries I’ve looked at seem to have a intercommunication system and I presume they supply the cables for that in their kit. Reliable cables are not always easy to fabricate on-site, so I can see why they might want to encourage you to keep the batteries close together.
I also don’t know if a webmaster wrote that after surfing the net or after asking an EE. You have to suspect everything you read online - including my posts!
I’m suspicious that they may just be using the mystery to get people to make neat and well thought out installations. And I do think that is very good advice.
I have to say, though, that with lead/acid batteries you could probably mount one at the top of the mast and one in the bilges and as long as you wired them up right you would probably notice no electrical degradation. (I obviously don’t actually suggest it.) And anything with a BMS should work even better.
I have worked with voltages and power supplies from 0.3VDC to 15,000VAC but have not worked with lithium batteries, so if an EE from OceanVolt can explain why it matters, I will defer to them.
I’m at the boat now, so it’s time to check on that lightning cable we were talking about last week. And try to suck the gunk out of my deck drains…
I believe the problem with treating the different locations as separate battery banks is that you want to be able to combine them into what’s effectively one higher amperage unit in order to conveniently get maximal running time.
You could, I suppose, keep them separate and simply switch from one to the other when the first was exhausted. But that’s not terribly convenient, and you’d have to do the switching every time (for both running and charging). Wiring them to charge properly only has to be done once.
The above pictures illustrate how I planned mine and then did it. There are two rows, each wired in series to compose a 48V 100Amp bank from four 12V 100Amp batteries. Those are then both connected in parallel to a bus, ganging the two 48V 100 Amp sets into what the engine and charging system sees as a single 48V 200Amp battery**.**
It may be a little confusing because I drew it envisioning positive on starboard and negative on port, but then ended up installing it mirrored because it turned out to be more convenient. So, as the photo shows, the positive wiring was actually installed on port. It leads forward to both the motor and the charging system from the 250A power fuse in the lower left of the picture.
Tim, with a Classic, wanted to run both positive and negative along the starboard side of his engine compartment, I suspect because that’s where the Classic layout makes it convenient to put the charger. That’s where a Classic has its house batteries and their charger, so you might as well put all the electrics together. On the other hand, on a 26 Ultra, the layout puts the electrical system on port, but there’s nothing about that system which constrains the negative battery cables and so it’s easier to save on expensive heavy wiring by keeping it symmetrical. My guess is that my wiring plan uses a couple of feet less battery cable than Tim’s. But, I don’t think either of us will have charging problems.
Bob - my install took exactly 25 feet of yellow 2/0 cable and 25 feet of red 2/0 cable. Going back and forth across the transom running cable forward from my transom-mounted busbars busbars used up both spools I bought on Amazon. I wish I had about another two feet of red wire, but a mistake in measuring early on left me with a pointless “service loop” at the aft end of the starboard lazarette. If I had not goofed up there, I think I would have been very happy with 25 feet.
Tim Cordes
Nonsuch e26C #32 “ENCORE”
Ford Yacht Club, Grosse Ile, Michigan
I don’t have my records, but I think mine was closer to 15-20 ft.
The Classic layout may have cost you more in wiring, Tim, but the benefits you got in placing the battery weight further back are probably well worth it.
Well, finally wrapped up my Electric Yachts QT10 install and completed sea trials. Went for an overnighter of about 15 NM distance. Very pleased with the outcome, it’s better than expected. Very light winds on the first day, and thanks to you Mike I tried your technic of providing miniscule power to sync the prop with the boat speed. I found it only required about .1 KW or less which was negligible to my power reserve. I noted the prop speed without power and moved the power enough to slightly increase the prop speed. Later in the trip the wind died all together so not being certain of the system capabilities and having time to reach my destination I set the power at about 1KW. This gave me a boat speed of 2-2.5 knots, and many hours of motoring. I connected the generator the next morning to charge through my 20 amp charger for about an hour. The second day there was plenty of wind (double reef at one point) but I still used the technic of syncing the prop speed to boat speed and was getting stellar performance. From open water to my slip is about 2.5 - 3 miles which I motored at 4 knots using about 2 KW of power. The tide was with me so I think my 4 knot speed may require 2.5 KW on still water. All said and done I still had 60% of my 200AH supply remaining when I tied up in the slip. The motor worked perfectly, possibly even better than the old diesel, and the motoring was much more relaxing without the feeling of needing to rush. My original design didn’t call for solar and this trip confirmed that decision. Solar would be the way to go for a long distance cruiser but that person would likely be doing so on a much larger vessel with plenty of room for solar panels. Charging at the slip and carrying a generator is the right solution for my sailing. I do have a single solar panel above my bimini for maintaining my 12volt system AGM batteries which keeps them topped up nicely. So three cheers for Ben Franklin for being brave (or naive) enough to fly a kite during a thunderstorm so that we can enjoy the benefits of electricity.
I will provide pics of the install as soon as I take them.
Do you mean that when you tied up at your slip, you had batteries at 60% of full charge? The max that I understand you should discharge an AGM battery is 40% of full charge.
If the above is true, you depleted at least 2/3 of battery capacity. That assumes you started at 100% full charge.
When you recharge batteries, they charge much quicker up to 80% of full charge than they do from 80% to 100%.
If you start with your battery at 80% charged, if my math is correct, you used 75% of available battery capacity for your recent trip (25% capacity remaining).
You might want to also consider increasing your battery charging capacity from 20A to 40A to get faster charging up to 80% of battery capacity. Your generator will likely support the larger charger. Maybe your existing charger is big enough if your system is 48 volts.
You misread my information. The 12 volt system is supplied by 2 Master Volt AGM batteries which are charged by a solar panel. My 48volt LiFePo4 batteries are the power source for my electric propulsion and as stated they were at 60% at the conclusion of my two day sea trial. They are charged by 110 volt at the slip or by portable generator when at sea.
