Electric motor for E35II

[Mark F]

I think its because they sell a la carte. Most other suppliers have complete units.

 

[Mark F]

These people were at the Port Townsend Wooden Boat Fest last year. I was impressed with their product.

Powerflow Marine | Electric Propulsion for Bluewater Sailboats

Bespoke electric propulsion conversions for bluewater sailboats. Four to six builds per season, built by hand in Port Townsend, WA. Jack and Sonya completed a 10,000nm voyage on a system built in this shop.

www.powerflowmarine.com

 

[johnnyL]

My A4 is finished.
As noted in a parallel thread I'm considering swap with a rebuilt.

I am also exploring conversion to electric, which in many ways makes more sense.
I only need to get in and out of the harbor for daysailing.
Seems like 200ah for would do it (for now)
Maybe a portable gen for range extension.

However, I'm seeing a substantial variation in Li battery prices.

When shopping for conversion kits and services, around 48v x 100ah, price ~ $2,000.
Others (for example several brands on Amazon and Battery Warehouse) as little as $150 for 12v x 100ah, so 4 in series ~ $600.
[and there are also 12v x 200ah for ~$300]
That would make Li cost just about equal to AGM.

That's a really big spread..
Anyone know what accounts for the big diff in battery prices ?

thanks

You’re seeing that spread because you’re not actually comparing the same thing, even though the labels look similar.

The big differences come down to cell quality, configuration, and what’s bundled.

Most of the ~$2,000 “48V 100Ah” marine / conversion batteries are:

Grade-A prismatic cells

Properly engineered internal busbars
A high-current BMS (often 200–300A continuous)

Enclosure, certifications, support, warranty
Designed for traction / propulsion loads, not just house loads

The cheap $150–$300 “12V 100Ah” batteries are usually:

Smaller cylindrical cells (often recycled or mixed grade)

Lower current BMS (100A is very common, sometimes less)

Fine for house loads, not motor loads
Marketing focuses on Ah, not discharge capability

When you put four cheap 12V batteries in series, you do get the voltage — but you don’t magically get propulsion-grade current handling. The weakest BMS or internal connection becomes the limiter.

What I’m doing (real numbers)

I’m using EVE-branded LiFePO₄ prismatic cells (similar to this: https://a.co/d/ahj6x1g — not the exact vendor, but same cell family).

Cell: 3.2V, 300Ah prismatic

Discharge rating: 1C continuous, up to 3C burst

Pack: Series configured for ~72–76V

That means:

300A continuous
Up to 900A burst (short duration)

I’m pairing that with a motorcycle hub motor rated:

8 kW 16kw continuous
Up to ~20 kW peak

For harbor in/out and daysailing, that’s plenty of torque and power, and the batteries are operating well within their comfort zone.

Why this matters for electric propulsion
Electric motors don’t care about “Ah marketing” — they care about:

Voltage
Peak current

Sustained current without voltage sag
Cheap drop-in batteries are fine for lights, refrigeration, and inverters.

Propulsion is a completely different load profile.
That’s why two setups that look similar on paper can be $600 vs $2,000.

Bottom line

LiFePO₄ can be cost-competitive with AGM if:

You understand C-rates

You size the cells correctly

You don’t rely on low-current BMS units for propulsion

If you want plug-and-play with warranty and zero DIY, you pay more.

If you’re comfortable building or specifying the pack properly, you can do it for much less — but the cells and current capability still matter.

~Johnny