Mixed Voltage Charging

malabarmcgyver · July 2019

I am strongly considering electric motors for my auxiliary power on my sailboat. I am planning to do some extended cruising, some of which will require motoring only, and not happy with my gas outboard. The motors are 48 volts / 4KW each and I plan to install two motors with a dedicated battery system of approximately 9216 WH each. I also have need of a house power at 12 volts. I plan to budget the house bank at the same 9216WH, primarily for consistency. I currently have a 12 volt / 400 watt wind generator and approximately 100 watts of solar and about 6 KWH of SLA batteries, as well as a 2K gas generator. I plan to significantly increase my wind and solar capacity for this project.

I plan to replace the 12v/400w wind generator with a 48v/500w wind generator and add a second one for a total of 1000w of wind generation at 48 volts. I have room for two 160w solar panels and plan a modification, in order to install 4 total solar panels. If charging the 48v system, is there any advantage of 12v panels vs 24v panels? This would result in 1.6KW of wind and solar generators. This also does not include the motors themselves, which regenerate while under sail or at anchor in currents.

My inclination is to setup all three battery systems the same with 16s 3.5v LiFePO4 180AH batteries and tailor the charging systems at 48 volts. I could switch charging sources to one or all of the three banks and for my 12 volt needs, I would run 48 volt to 12 volt step down converters for house power. There is a temptation to dedicate one wind generator and two panels to one bank - since there is one each for port and starboard. I would still need to switch one or both of them to the house bank for charging. This would give me redundant systems and likely be more expensive. By having one combined charging system consisting of both wind generators and all four panels, I could focus the power generated. This is the direction that I am leaning, but open to ideas.

The motors being evaluated are E-Tech 4POD and can be found here. I plan to use the outboard version in order to also use the engine as a tender motor, which will require another battery pack, engine controller, and throttle control.

I plan on using LiFePO4 prismatic batteries for everything. I am currently looking at these, which are CALB prismatic 180AH batteries. I would need 16 each of these for the three systems. I really won’t know until I get the first 16 in, but I plan to assemble them in groups of 4, or 12 volts, compression packs. This makes them more portable for me. I looked at the LiFePO4 pouches and they just do not appear durable enough for the environment that they will be in. The second, but significant part of this system is the battery management system.

Since I will need a BMS for each system and plan to have four systems including a portable 50AH pack for the dinghy, I cannot rationalize $600 or $800 for each BMS. I found this one, which does not include accessories, such as sensors and Bluetooth. I would like to have individual cell monitoring, balancing, and control.

Finally, I have to control the charging of each of these systems. I have read that the LiFePO4 do not like float charging nor full charging. I plan to only charge to 90% capacity - 3.45 volts, or 55.2 volts, but need programmable chargers/controllers or a BMS that can cut them off. Evidently overcharging and float-charging LiFePO4 batteries reduces cycles significantly. I just ordered a prepackaged LiFePO4 battery this week for another application and evaluation from a reputable lithium distributor and their charger will both overcharge and float charge, with no instructions to do otherwise. I was very disappointed.

I would appreciate any guidance that this forum can provide.

Thanks!

Jeff

Estragon · July 2019

In theory, using higher voltage panels would mean 2 strings of 2 panels in parallel, vs 4 12v panels in series, the former of which may handle shading from stays etc better. In practise, a 24v 160w panel may be hard to find. In either case, 4x160w panels might bring 4-500w, maybe 2kwh-ish/day to the charging party. Don't know about wind, you'd know better about what to realistically expect in your cruising grounds.

I wouldn't recommend two separate propulsion banks with independent charging. That seems likely to get complicated really fast. If using step-down transformers for house loads, I'm not sure of the case for a separate house bank either.

mike95490 · July 2019

After you do all the planning for electric, I think you may go back to 2 cycle outboard. That's an established, reliable tech, and you can get parts in any port. Batteries, panels, electronics, BMS, in a marine environment, I think will be a mistake at this time. Maybe 3 + years from now it will be different, but today, I'd stay at 2 cycle outboard.

malabarmcgyver · July 2019

Two separate propulsion banks is my preference for reliability. One combined and focused switchable charging system is preferred. I am looking to cruise for a day and then layup, possibly without shore power for a week to recharge.

Estragon · July 2019

I'm not seeing how two (or more) separate propulsion banks increases reliability. I could maybe see a case for say a lifepo bank for regular use and L.A. bank for backup to get me off a lee shore in a blow, but not seeing the benefit of separate lifepo banks.

malabarmcgyver · July 2019

I see it as little difference in keeping fuel and starting batteries separate on dual outboards. A BMS could fail, a cell could short or open, a motor could malfunction and drain a bank. It seems absolutely logical to me.

mcgivor · July 2019

The 180 Ah battery would provide ~ 1.7 hours use at full power, using a 75% operating window of the battery's maximum capacity, it would take an array or other charging source of equal capacity, 4KW, to replace what's depleted in slightly more time. Careful calculations would be needed to achieve satisfaction of requirements, remembering the limitations of both wind and PV charging and when being under power is required. To me at least, it would appear to be an extremely difficult challenge, not impossible perhaps, but difficult non the less.

Estragon · July 2019

Yup, all that could happen. But why stop at two? If two is better than one, wouldn't three be better than two, etc? It just seems to me that adding complexity is the last thing I'd want trying to claw myself off a lee shore.

That said, I'm always amazed watching sailboats motor by in wind without even taking the cover off the msinsail. Having had the iron genny let me down in a squall, I always assume the worst. Maybe I'm just lucky.

malabarmcgyver · July 2019

Yes, at full throttle I would have approximately 2 hours of run-time, not much. I have no intention of running at full throttle the majority of the time. I only chose the 4KW motors to overcome wind and tide currents on rare occasions. I was nearly stand-still one evening going under Jensen Bridge with 20Kt wind on my bow and several knots of current against me. At half-throttle, it is less than half the energy consumed - it is not a linear calculation. With consultation from the vendor and some estimates, I estimate 4-5kts at half-throttle, or 1200 watts for each motor. This would provide close to 8 hours of motoring, which I expect is worse case. If I get six hours, I am happy as a clam. I am hoping to do the interior Great Loop and it has many areas where I am not able to sail and in fact I must drop my mast during a few hundred miles of the trip.

I have performed a comparison of a high quality outboard against the electric setup and it is much closer to breaking even in the long run than you would think when you add fuel and maintenance. Initially, when I was comparing prepackaged batteries, I could barely come close on one system. The dual engines are also a much better match for the sailing catamaran as it can be a bear to dock with wind on my beam.

If you count the third house bank, which will be similar to the propulsion banks, then yes, I would have three separate banks. Is that necessary for reliability? - No, but I do not want to weigh anchor after a long day and not have enough juice to run my water pump for a shower.

I appreciate the comments and bid you all Happy Sails.

Estragon · July 2019

I can definitely see dual motors on a cat. Being able to reverse one side would make navigating in crowded spaces much easier. My beach cat has no engine at all, making for some interesting docking at times

Mixed Voltage Charging

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