Never thought of fiddling with field voltage. But there are many buck supplies available with adjustable outputs - need one that delivers field current needed.
All car electronics are suposed to be protected to impulses of 42v so assume that is a bit more than worst case alternator can generate. Thus 24 v seems reasonable. 36 is probably pushing it. Get dc by adding new diode block. Full wave bridge with current rating roughly double what is to be drawn. 100a 100volt diodes seem close. Could chase up a synchronous rectifier using big MOSFETs but that is complicated but you get huge reduction in heating rectifier block. Suggest adding smoothing capacitor. Voltage rating at least double the output voltage. 1000uf is my pure guess. Only needed when running electronics without battery present. Can also run a voltage doubler circuit but the primary peak currents get real high so both alternator and diodes will need higher ratings. There are now many boost dcdc that might be better to take 12 or 24 to minimum charger voltage
Best regards
Lee Eldridge
0427874796
On 6 Jun 2025, at 23:40, Kevin Pemberton via groups.io <pembertonkevin=gmail.com@groups.io> wrote:
Making an automotive alternator produce higher voltages is quite easy. No rewiring is needed, the secret is in the regulator. This is how I have done it.what I have used it on is 24 volts, but anything the diodes will handle will be possible. in the, day this was proven high enough voltage to run power tools using a box that disconnected the cars electrical system while powering ac/dc tools for remote use.setting the small engine RPM to an RPM that the alternator will produce the voltage required is first step. second step is to adjust a small DC to DC power supply to a voltage that will drive the field for an output from the alternator that you desire, at 29 volts that voltage is roughly 5 volts.I suggest belt drive..you will choose an alternator that is old school(No regulator). Chrysler was first in the alternator builds, so that has been my choice, but any alternator will do. you can bypass the original regulator on any of them.things to remember.a 60 amp auto alternator will produce 3600 watts at 60 volts, and 864 watts at 14.4. The wire size should be maintained and only 80% of the alternator capacity used(duty cycle). so use a current limiting circuit( I use 12 awg wire with silicone insulation). I suggest using an alternator and engine that will just keep up with cruise speed wattage requirements, or less depending on battery pack, and cruise distances expected. I don't believe the engine will be running in optimum RPM range so will likely be in the 8hp range.hybrid has been my design choice. So spent plenty of time on researching answers.Agree that it is a sane idea to have such a backup. Particularly if the boat is your home and nest. You will need then an AC to DC charger that will add $$$.Alternately you could construct one from say a small Honda motor and a a rugged off road car alternator plus a DCDC charger. A 3kw motor should drive a 200A (14v) alternator. Say use a 250Amp alternator to drive gross charge into batteries. I am sure one of the subcontinent youtube videos will show you how to rewire an alternator to give higher voltage. ~48 I can see happening without too much strife.It will be interesting to see a 72v alternator built on the body of say a 300W car alternator.. Easy to make rectifier using BIG diodes. Indeed someone could cobble up a synchronous rectifier using 300v 200A MOSFETs. Add some current sense and code running in an Arduino and you have a monster charger system. Water cooled of course. Possibly there is an app note on building a 13.8v dc to 72vdc inverter with 40A output.I have been watching how it is done in "Sailing without a motor": https://www.youtube.com/playlist?list=PLARfxaCYDjDygPQrWVZEqc334JXh0UiTK I see what he does and has done but I feel nervous when he goes near hard things like bridges, rocks and other vessels.
On 3 Jun 2025, at 10:11 am, Scott E Erdman via groups.io <seerdman=syr.edu@groups.io> wrote:Not what the original intention is but a useful backup and maybe needed for some circumstances is a small gas generator- I have a Westinghouse igen 2500 - will help compensate for situations where motor is the sole option (rivers, currents, straight upwind with no option to tack). I keep mine in the starboard locker.
On Jun 2, 2025, at 3:52 PM, David E Marsland via groups.io <david.marsland=gmail.com@groups.io> wrote:
I installed an Electric Yacht Quiet Torque 10 KW motor for my Catalina 27. This would probably not be nearly big enough for your boat. 20 kW sounds like a better bet. It's also a 48 volt system. It's worked out great for local sailing with two 5 kilowatt hour LFP batteries in parallel.
For cruising I'm going to add another 10 kWh of LFP batteries.
The one thing I would caution about going higher than 48 volts DC is that it's very difficult to find electrical components such as switches rated above 48 VDC at high current. Even finding 48 VDC switches is challenging. Many top out at 32 volts.
I charge at the dock and have solar for backup. Theoretically it will regen when going over five knots under sail. Unfortunately I'm going to have to change the propeller to make that work.
All the best,
David
I have researched electric motors for boats a number of years. MY choice for my 32' Buccaneer, which is still being restored, is the Electric Yacht QuierTorque 20.0. It's 48 volts, 400amps current. Maximum power input is up to 20.0 KW, it will accommodate 3/4 to 1.5" shaft size, it weighs 135 lbs. It has two motors in tandem that you can cruise with one motor or both, depending on your speed and current and sea condition. 7.1 knots is my boats hull speed. 6.0 knots can be supported by a 11KW 48 volt gen set. At that speed, it takes 190 amps and 9120 watts. The motor will fit in where the engine would sites on the runners. The cost is about $9K. I think it is the most reliable on the market but that's just the opinion I've developed over the years. Good luck!Dale
On Mon, Jun 2, 2025, 4:25 PM Kevin Pemberton via groups.io <pembertonkevin=gmail.com@groups.io> wrote:
You might want to visit sailing Uma. It is a YouTube channel. They started with a golf cart motor.
On Monday, June 2, 2025, cammcnally10@outlook.com via groups.io <cammcnally10=outlook.com@groups.io> wrote:
Hi everyone,I am restoring a C&C 40' sailboat on a budget, and I am planning on replacing the engine with an electric motor. I know some of the general specifications I would like, including Brushless DC, 48V, and 12 kW. Does anyone have experience or advice on repurposing motors from golf carts, forklifts, or other similar vehicles? I have briefly searched eBay and online motor catalogs.Any insight would be much appreciated.
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