Heltec BMS "idiot check"

[Indefatiguable]

Ah shite. Yep was reading on the left.

Dude thank you. 1000a rec bms it is.

I'm gonna have to redo my range projections and likely my bank design to compensate.

This is why this forum is awesome, you just saved me x wasted expense and y crappy headaches.

Thank you.

 

[Indefatiguable]

Dude using that graph what are your thoughts on swapping the belt pullys from 1:1 to 5:1 (5000 motor/1000 shaft), seems like that'd be more efficient. I suppose that'd be reducing effective torque from 105 to ~15×5 though. Hmm.

 

[justgary]

Dude using that graph what are your thoughts on swapping the belt pullys from 1:1 to 5:1 (5000 motor/1000 shaft), seems like that'd be more efficient. I suppose that'd be reducing effective torque from 105 to ~15×5 though. Hmm.

Sorry I burst your bubble, but I'm glad to see that you are able to adapt.

2:1 reduction will double your torque at the shaft and half the speed, so that might be good. You mentioned that your transmission already has a 2:1 gear, so I would probably run the motor at 1:1 into the transmission.

I would try very hard to keep the original running gear in place so that you don't need a new prop or shaft. Looking at the chart again, it looks like the motor produces the best torque below 2000 RPM, which is similar to your diesel. Note that the horsepower drops off above 2000 RPM due to the much lower torque, suggesting that they don't really intend for you to run it that fast.

The big question is the battery capacity and how you charge it. Sourcing 200 to 700 Amps to run the motor is a pretty big deal. You'll need 48VDC and 700Ah per hour, which is 34kWh per hour of use at 1800 RPM. How do you plan to charge that in a reasonable amount of time?

Note that the curve does represent the maximum power the motor can produce (in other words, you can spin the motor to 2000 RPM with no load and it will use a lot less current). Your diesel is rated at 52 ft-lb torque, which is roughly half of the rated output of the DC motor. It might be reasonable to expect your maximum current draw to be more like 450 to 500 Amps. Still, that's 24kW per hour.

 

[Indefatiguable]

Few things,
The gearbox from the old volvo is already gone, just have a keyed end of a prob shaft hanging there. The kit I bought came with a coupler and thrust bearing as part of the new belt drive.

Applicable piece:

Home :: Gear Reduction & Motor Plates :: 12-24KW Gear Reduction

Belt Drive Now Standard High torque drive belts and pulleys are now included in our reduction kits These are strong quiet solutions for sailboat conversions If steel chain is preferred please contact us for pricing and availability What is a gear reduction? Mounting assembly for the sailboat

www.thunderstruck-ev.com

I have spoken with them and can order belt wheels/belts to my hearts content to play around with the gearing.

When I looked at the chart after the last post it looked like around 3.5:1 might be the most efficient. It'd net around the same torque at cruise speed, and a good bit less draw (360ish vs maybe 560 1:1)

A key note to this project is that the motor is an auxiliary propulsion system, the sails are for long hauls. The motor is for going in/out of marinas, powersetting the anchor, and emergency/close quarter manuvers.. I can plan a weather window pretty good for island hops, and the runabout dingy I'll have hung on the stern davits has a 20hp outboard should all else fail.

Charging systems include 3x rec alpha 400 panels (boat will be in tropics, mounting location is great) 2x 400w wind turbines, and a 50w pedal generator from kpow for backup.

Battery bank was going to be 16s calb 100ah but I might spring for 300ah cells now. I've read that the larger the cell capacity the more susceptible it is to vibration/shock/impact damages in a mobile application. A bms that could handle 1000a 16s 2 or 3p would be ideal as then I could run more durable cells, but barring that I'd be willing to run the 300ah ones inside a multi layer vibration/impact isolating box (integral rubber mounting or some such finagelry).

I think another key note here is, as you said, the graph represents maximum draw not constant draw. As the boat gets moving its 18000 lbs sliding through the water will act as a big inertial modifier to the numbers we're crunching. Another note is the general rule of thumb that every knot of speed doubles (or halves when reducing) the fuel or power consumption. I may keep the 1:1, I may change it, I'll probably end up with 3 or 4 sets of wheels/belts lol - but I will almost never be running flank speed inside a marina xD

 

[Indefatiguable]

Also, it's important to remember the existing/old drive system was rated at 52 ft lbs at 2000rpm *at the crank* then put through a 2:1 reduction, resulting in the actual prop spinning 1000rpms with 104 ft lbs pushing it. Those are existing parameters (104 ft lbs / 1000 rpm) I'm trying to match so as to not need a new prop.

 

[Indefatiguable]

Ah yes I forgot hydrodynamic generation (yes controller is capable). Hard to get exact numbers, but from looking at other people's systems I estimate around 200-350w while sailing.

The whole charging issue is really pretty tricky. Boat gets anchored in the Lee (hiding from wind) of some island, and sails furled. So zero wind generation, zero hydro generation, near full (realistic) solar generation.

Then I weigh anchor and am underway with sails up, shading anywhere from none to 100% of solar array. Wind/hydro generation come into play here for a period of a few hours to weeks depending on the specific passage.

So power generation becomes much more complicated to place an accurate projection on even compared to the normally very situational home solar array.

I think the key to a successful system in this application depends on battery bank capacity. I also think 200a draw for an hour is as low a figure I can calculate based somewhat in reality.

This means I need a 48v bank of as high AH as possible, ideally beyond 400ah capacity. Being able to store power for multiple "sessions" of motoring (into slip/mooring or exploring an achorage and powersetting anchor) seems like an important feature. Soaking in tropical sunshine for a week to charge said bank is easy.