Replace 5kwGenny with high output alternator

[km1125]

Source of the post ...
Battery recharge in about 3-5 yrs will be down to 5-10 min on the engine (See BYD EV Recharge) using the high output alternator. ...

Yea, I'm not buying that part. Eventually we'll see solid-state batteries that can have very quick recharge times. They're out there experimentally now, but we haven't seen all the limitations yet in real-world operations. And I'm not sure something like that might even be affordable within the 5 year timeframe. We might see them in EVs, but only because of the industry-scaling advantages.

But lets just say there is a battery that can be recharged in 5 or 10 minutes and it's a 10kWh battery pack (not very big)

To recharge 80% in 10 minutes you'd need a 48kW generator (or alternator) running at 100% or for 5 minutes 96kW generator (alternator) Neither of those would be belt driven off a gas or diesel engine, they would have to be direct-drive or a gear-driven unit.

[Alanna Mo Cree]

Source of the post To recharge 80% in 10 minutes you'd need a 48kW generator (or alternator) running at 100% or for 5 minutes 96kW generator (alternator) Neither of those would be belt driven off a gas or diesel engine, they would have to be direct-drive or a gear-driven unit.

That's a lot of amps (or a lot of volts). The BYD architecture uses 1,000 volts and some serious cooling. Definitely doable as part of a complete system, but not something that is likely to be dropped in to an existing platform.

5-10 minutes recharge doesn't really matter for boats anyway though unless you also consider electric propulsion. As long as the battery is being charged while the main engines are running or shore power is plugged in, there is plenty of time for charging. Storage is the main issue IMHO. Despite Victron supporting up to 256KWh with their batteries, it currently takes too much space for practical power storage on 30-50 foot boats if you want to be able to go days or more running all of the modern amenities without charging.

Now combine fast recharge with significant power storage and it will really change how we think about energy. That's why I'm looking at 10 years as the timeframe for the next big electrical upgrade. It wouldn't surprise me if I switch out the gas engines and high output alternators for electric inboards and a diesel generator at that time.

[GFB]

One thought in addition to Alanna's comments is the factor of maintaining a third engine inside a large box that eats gas and maintenance, not to mention weight. High output marine alternators (up to 200amps best in class), on small solar/battery systems like mine (400amp/hrs) recharge time is 2hrs max.

Unless I'm missing something my generator only kicks out approx 40amps at best. Basically incredibly inefficient.

On my Mariner 350 I've dumped my 200ft of anchor chain for 50ft of chain with a rope rode (saving approx 230lbs). Add in the weight of generator (300lbs) and I'm no longer pushing around about a 500lbs of dead weight. Boat handles better, eats less gas and specifically is not in for repairs as much (again for the generator).

Side note on the Mariner: Tends to ride nose heavy so the lack of chain helps greatly.

Currently a single 200amhr battery weighs 44 lbs. I have two of these. From my original post this lasts me a week on the hook. So weight is not a consideration on the battery side.

BTW if my math on the Genny is wrong please let me know. I'm trying to cover all angles and not so good at math...

Note: all weights courtesy of Chrome Gemini AI.

[bud37]

Source of the post Unless I'm missing something my generator only kicks out approx 40amps at best. Basically incredibly inefficient.

That is 40 amps as you say at 120 vac......a charger that puts out 60 amps at 12vdc works off a 15amp at 120vac fuse and is capable of maintaining around a 500-600 AH bank according to the promariner manual.

If you have a 7.3 then you are talking about output around 60 amps at 120vac I believe if I remember right, that is what we had in our 350.
Not sure if this is what you are asking about but there is some shaky info from my old brain.....

[Alanna Mo Cree]

I think discussing amps and amp hours gets confusing. At least with 12v and 120v systems, the amps are easily translated. A 30A shore power (120v) is theoretically capable of providing 300A at 12v. Either way it is 3.6KW which leads to why generators are sized the way they are. The KW is what really determines the power and generators are typically sized around the corresponding shore power specifications.

I was recently discussing our electrical upgrade and was asked how many amp-hours I'm putting in. When I said 400, the person I was talking to didn't think it would be nearly enough for what we wanted to do. The important piece of missing information is that my system will be 48v and not 12v, which is 4x more capable. And in actuality, a "48v" system is really 51.2v so we have a theoretical max KW storage capacity of a little over 20KWh. No matter how we use that storage across 120v or 12v loads, the storage is what it is.

Boat life was so much easier when everything was 12v!

[bud37]

Source of the post Boat life was so much easier when everything was 12v!

You said it....one thing I know for sure, if you take the power out then ya gotta put it back at some point, somehow, no free energy according to the physics laws I am aware of anyhow....

Keep us updated on the workings as you go, interesting.

[Alanna Mo Cree]

I just looked up my pic of the Kohler 7.3e that has been removed from my boat.
60Hz
3600 RPM
Gasoline

Continuous rating based on a maximum temperature rise at rated load of 120 degrees C. Altitude 500 feet.
Single Phase 25C = 7.3KW and 7.3KVA
Voltage 120/NA and 60.80A

So this is "a third engine inside a large box that eats gas and maintenance, not to mention weight," but it is more efficient than producing equivalent alternating current from a DC alternator attached to a much larger engine that then needs to go through an inverter with the associated losses and what-not involved. The Kohler has a relatively small 2 cylinder engine. My mains are 375HP 8 cylinder engines.

Whether to replace the generator with H.O. alternator(s) really comes down to how the boat is used. If my family spent any significant time anchoring or otherwise away from shore power, I would definitely lean towards fixing or replacing the generator. My preference would be to replace with a low RPM diesel of about 3KW, but there are a lot of additional considerations when putting a diesel generator in a gas engine compartment. The most economical decision would be to fix the existing generator, followed by replacement with a gas generator even if they are $20k-ish new these days (actually on sale for about $15k at the moment).

If you are able to store enough energy to power everything you want to run in between regular use of the mains, then I don't think you can go wrong with H.O. alternators instead of a generator. You are going to be running the mains anyway, and the worst thing to do to a generator is not use it. The strongest consideration is how often you end up running a main engine just to generate electricity, and if that additional wear and tear on a big engine is worth not having a third engine. The cost for both of our H.O. alternators with external regulation and professional install by an ABYC marine electrician is less than the purchase price of the new generator by itself.

My strong disclaimer at the moment is that I don't yet have the first hand experience from our upgrade. We've been waiting on some rudder and through hull work to finish before the power station is installed. Once the upgrade is done, I'm sure I will know pretty quickly whether I made the right decision to ditch the generator. Hopefully I don't start referring to it as a downgrade.