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Marine Electric Propulsion Solution

ArranP

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Nov 5, 2020
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I installed my off-grid residential solar system. Battery, inverter & charger are all on 48VDC so pretty straight forward.

I'm currently working on installing an electric propulsion system on a boat, basically the residential loads are similar + there is the additional load the electric motors.

The difference I am up against at the moment is that the VDC is alot higher, the electric motors are 96VDC upto 144VDC @ 60kW, so I'm into new territory as regards to selecting inverter, charger and solar panel setup and I'm am as yet unsure as to wether these components are available at these higher voltages.

At the moment I have more questions than answers and I welcome comments from others.

Regards
Arran.
 
12V to 48V are more common, and there are 400V systems. Probably some in between, pretty sure 120VDC has been done, just don't know what to recommend.

How about assembling two, 48V systems (of a type that tolerate floating battery voltage) and connecting them as +/-48V? That should run your motors and power inverters.

Maybe, just maybe, a pair of inverters each running on 48V (one positive ground, the other negative ground) could be stacked for 120/240V of more power. This would require their communication bus to be galvanically isolated. Or for you to make an isolator card to go between them.
 
Depending on the size of motor you want there are some that run on 48V.
I did not want to go above 48V to be able to use of the shelf components and found electric motors up to around 20kw continuous power.
 
Electric motors come are rated and max rated.

When working with liquid cooled electric motors can the max rating be used as the rating for continuous use ?

I am being told that due to the motor being liquid cooled it can be run continuously at the max rated.
 
I installed my off-grid residential solar system. Battery, inverter & charger are all on 48VDC so pretty straight forward.

I'm currently working on installing an electric propulsion system on a boat, basically the residential loads are similar + there is the additional load the electric motors.

The difference I am up against at the moment is that the VDC is alot higher, the electric motors are 96VDC upto 144VDC @ 60kW, so I'm into new territory as regards to selecting inverter, charger and solar panel setup and I'm am as yet unsure as to wether these components are available at these higher voltages.

At the moment I have more questions than answers and I welcome comments from others.

Regards
Arran.
Did you figure this out? I am in the process of doing the exact same. Looking for a full 96v system

- 96v Solar Charger
- 96v Inverter

Would love to hear where you end up.
 
IP21 and IP30, not much protection for water environment.

There's lots of 48V equipment available, some sealed, which is why I suggested +/-48V (middle grounded to chassis). That makes 96V available to boat motor, while chargers and inverters can be 48V.
 
No Ides if they are good / Dependable. but found these

Found this so far. No idea if they are good or not.
96v Solar charger - https://www.inverter.com/40-amp-96v-mppt-solar-charge-controller
96v Inverter - https://www.inverter.com/6000-watt-off-grid-solar-inverter
I got as far as finding that inverters operating at this voltage are most likely give a 3 phase output, e.g Growatt are a manufacturer that make high voltage 3 phase inverters... https://bluesunpv.en.alibaba.com/pr...w_20kw_three_phase_power_inverter_system.html
 
IP21 and IP30, not much protection for water environment.

There's lots of 48V equipment available, some sealed, which is why I suggested +/-48V (middle grounded to chassis). That makes 96V available to boat motor, while chargers and inverters can be 48V.

Please elaborate, I have no knowledge on how to combine two nominal voltages 96VDC / 48VDC i.e. 96VDC motor 48VDC inverter/charger...
 
Please elaborate, I have no knowledge on how to combine two nominal voltages 96VDC / 48VDC i.e. 96VDC motor 48VDC inverter/charger...

Let's say you built a 48V system, with negative terminal grounded to chassis. Positive terminal is at +48V or so. It can be charged by a battery charger.
Then you build another identical 48V system but ground the positive terminal. It's negative terminal is at -48V or so.

There is now 96V between positive terminal of first and negative terminal of second. Much like getting 3V from two 1.5V flashlight batteries, but we grounded the midpoint.

One problem with this would be the two 48V batteries won't always be same state of charge; one could be completely drained while other still has charge, and continuing to use the 96V propulsion system would do bad things to the drained battery.
So long as each has a BMS that disconnects at low voltage (and the BMS tolerate being series connected), that shouldn't be a problem.
 
Let's say you built a 48V system, with negative terminal grounded to chassis. Positive terminal is at +48V or so. It can be charged by a battery charger.
Then you build another identical 48V system but ground the positive terminal. It's negative terminal is at -48V or so.

There is now 96V between positive terminal of first and negative terminal of second. Much like getting 3V from two 1.5V flashlight batteries, but we grounded the midpoint.

One problem with this would be the two 48V batteries won't always be same state of charge; one could be completely drained while other still has charge, and continuing to use the 96V propulsion system would do bad things to the drained battery.
So long as each has a BMS that disconnects at low voltage (and the BMS tolerate being series connected), that shouldn't be a problem.
Not sure I understand this, Would need a diagram. Also out of balance 48v packs is a no go from my understanding. Would love to hear more. You have my full interest
 
Let's say you built a 48V system, with negative terminal grounded to chassis. Positive terminal is at +48V or so. It can be charged by a battery charger.
Then you build another identical 48V system but ground the positive terminal. It's negative terminal is at -48V or so.

There is now 96V between positive terminal of first and negative terminal of second. Much like getting 3V from two 1.5V flashlight batteries, but we grounded the midpoint.

One problem with this would be the two 48V batteries won't always be same state of charge; one could be completely drained while other still has charge, and continuing to use the 96V propulsion system would do bad things to the drained battery.
So long as each has a BMS that disconnects at low voltage (and the BMS tolerate being series connected), that shouldn't be a problem.
Rather like connecting in series, is there any reason to stop at only 2 in series, i.e would it be possible to connect 3 in series or 4...
 
I installed my off-grid residential solar system. Battery, inverter & charger are all on 48VDC so pretty straight forward.

I'm currently working on installing an electric propulsion system on a boat, basically the residential loads are similar + there is the additional load the electric motors.

The difference I am up against at the moment is that the VDC is alot higher, the electric motors are 96VDC upto 144VDC @ 60kW, so I'm into new territory as regards to selecting inverter, charger and solar panel setup and I'm am as yet unsure as to wether these components are available at these higher voltages.

At the moment I have more questions than answers and I welcome comments from others.

Regards
Arran.
I had the same thoughts and ended up using a 48V motor; or better said a PMAC motor witha SEVCON Gen4 controller that can be programmed between 48V - 120V.
Main reason was to use off the shelf 48V equipment and liability / insurance issues. Rumours have it that 48V systems are classed as "ok to be build by layman" where as above 48V a professional is required.
 
Rather like connecting in series, is there any reason to stop at only 2 in series, i.e would it be possible to connect 3 in series or 4...

I haven't built this or any other lithium battery, so just thinking it through.

Some people build a 48V system with four, independent 12V batteries each having its own BMS.
Only some BMS allow that; I think the problem is that it's disconnect switch sees the full 48V.
Within each 4-cell 12V pack, the BMS provides some balancing. But there is no way to balance between 12V batteries. If SoC drifts too far apart, BMS would disconnect to prevent overcharge even though pack voltage seemed OK. The 12V batteries would require occasional independent (or parallel) recharging to top balance.

Unlike that 12/48V configuration, your 48/96V would always have separate recharging of 48V batteries. Each day they would be independently recharged to the same SoC. Also, they can be drawn down at different rates with separate loads (48V inverters), or maybe one would serve as your house battery and the other would never see discharge except by the 96V motor.
Each 48V BMS would need to be able to disconnect loads (96V motor, 48V inverter) for over-discharge of a cell, and charger for over-charge.
That disconnect would have to handle the 96V+ of a full pack (with its internal transistors, or external relay)
With 48V BMS, it could communicate with its associated charger (and inverter if there is a reason to.)

A 96V BMS could also be used, but probably couldn't communicate with separate 48V chargers because the two 48V sets of cells would be of different SoC. Also, only isolated communication could work; if electrically referenced to negative terminal of battery, one 48V charger would be offset.

Like for 12/48V, there would be limit on how many in series because each disconnect switch sees full voltage of the whole battery.
With multiple 48V chargers/loads, each needs its own disconnect. If using a 96V (or higher) BMS, its disconnect signal would be used for relays on each 48V circuit.

This would work with lead-acid as well, but the problem is that entire battery voltage is the only way low SoC is detected, so with one 48V pack lower than the other, it would be over-discharged. A BMS (or monitor) of each 48V pack is required to stop discharge of the 96V battery when either 48V battery is fully discharged.

Main reason was to use off the shelf 48V equipment and liability / insurance issues. Rumours have it that 48V systems are classed as "ok to be build by layman" where as above 48V a professional is required.

I consider this a 48V system. Twice. :)
By grounding the middle, and using relays/fuses to disconnect at either end, the highest voltage is 48V nominal. or -48V nominal.
The only way you get 96V is by grabbing both wires.
Similar to house wiring - nothing is 240V; all wires are 120V, just of different phases.

If 10kW propulsion motor is the largest load, using 96V cuts the current in half compared to 48V, and the power loss (heating of wire) to 1/4.
 
More research - Here is what I found. Would love your input. Writing this down so I have it in one spot for you to scrutinize and tell me I am wrong. Have at it :)

1) RE: the Center Tapping or 48v and 96v on a switch system. Did about 10 hours of research on this one. Nobody seems to believe this is a good idea due to complexity and out of balance issues. PUTTING THIS IDEA TO SLEEP - cannot find any data to suggest viable / dependable

2) RE: 48v full system - 90% of the time best idea. Here is why

(YOU ARE NOT PLANING ON BATTERIES FOR MORE THAN 10 mins even with 100kWH battery and Dual 144v motors. GIVE UP ON THIS IDEA)
  • Many quality turn key systems. This has been done 100's of times. Proven. So many options. Safer
  • 48v system will max out at 12kw Motor, 16hp (48v at 250amps continuous with say a ME1616 motor) - which will be enough for max displacement for almost all hulls - NOTE: You must ignore the motor peak amp numbers such as running it at 500amps.... 12kw is your sustained max on 48v.....
  • Calculate your Displacement HP / Speed here - https://vicprop.com/displacement_size_new.php
  • Note, 1kw = ~1.34Hp
  • These Examples put this into perspective how little gains you get after Max Hull Speed. This is with a 85kWh battery
    • Very small gains for increasing Motor Output over Hull speed. For a 20 foot boat.
    • 6.8kw motor -10hp (Hull Speed 20foot displacement)= 7mph, 86 miles, 12 hours run time
    • 12kw motor - 16hp = 8.4mph, 60 miles, 7 hours run time
    • 24kw motor - 32hp = 10.4mph, 37 miles, 3.5 hours run time.

3) RE: 96v system, the other 10%:
IF you have a massive battery, AND your distances are short, AND it is worthwhile to get there at 3 miles an hour faster. THEN this may make sense for you to jump thru the hoops for a 96v system.

I will be commuting 9 miles daily with my Electric boat so still want to explore this option. I have 2.2kw Solar array on my boat.

96v Solar chargers No idea if they are good. Any input? Other suggestions?
  1. - Super expensive. Water proof
  2. - Residential, but has a 96v version - MASTER-96BH-50A
  3. - Very High Voltage.
  4. - Has a 96v version (96BH-50A). Industrial and Waterproof. -
  5. - No much info
96v Inverters.- Could not find many at all. Any Suggestions.
  1. - Looks cheap, but does 96v 6000w and has 96v 30a Charger as well.
  2. -Looks Suspect from amazon....
  3. - Looks really nice
  4. -CHEAPO China.

32s BMS - ????
300 amp DC 96v Breakers ????

OK. lets here feed back.
 
32s BMS - ????
300 amp DC 96v Breakers ????

REC has BMS master/slave modules for up to 240 cells in series.


Class T fuses cover your voltage and amperage.
Are your batteries one string, or more in parallel? Class T fuses are 20,000 AIC. I think one lithium cell can deliver 20,000A into a short (but haven't seen spec or test results.) Separate fuse per string might be better, but then you couldn't do 2p32s, just 32s2p.

Switches of such rating are also hard to come by, but there are heavy-duty 600V AC/DC 200A 3-pole switches.

Midnight has a 125V, 250A breaker. How much do you really need? That would let you draw 19kW and have 25% headroom.



Different approach, what if you had a 400V battery, 3-phase motor, and variable frequency drive?
(Yes, there are inverter/chargers for that.)
 
More research - Here is what I found. Would love your input. Writing this down so I have it in one spot for you to scrutinize and tell me I am wrong. Have at it :)

1) RE: the Center Tapping or 48v and 96v on a switch system. Did about 10 hours of research on this one. Nobody seems to believe this is a good idea due to complexity and out of balance issues. PUTTING THIS IDEA TO SLEEP - cannot find any data to suggest viable / dependable
When both inverters are connected to the same 96V battery then batteries becoming out of balance is non issue as there is only one battery.... Not that I am promoting this idea, just that I had thought about this and concluded that balancing is a non issue when using one battery.

Scrub this comment... the 96V battery will receive its charge via two 48V chargers one connected to the first half of the battery and the other connected to the latter half of the battery, and then rely on its 96V BMS to cell balance. So the time it takes the BMS to cell balance would need to be compared with the batteries usage cycle to determine if the cells will be balanced in time for use.
 
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Took the first step. Contacted this company. They were extremely helpful. My Mars 96v 50amp Waterproof ip67 Solar Charger with WIFI / App + PS monitoring will be shipping from China Next week. Product looks good. We will see..... SKU - (96BH-50A). Industrial and Waterproof. looks like they just released a new version as well with updated software. Verified app and pc program are in English as well. Company even answer emails. They seem good.

Now just need 96v Inverter and BMS system.

www.solarcontroller-inverter.com

I-Panda 80A 12V / 24V / 36V / 48V Outdoor Waterproof MPPT Solar Charge Controller

This is the Maximum Power Point Tracking (MPPT) feature with a highly efficient MPPT charge controller. It has the advantages of self-cooling, automatic identification of system voltage, wide range of PV input, various battery charging, intelligent discharge control, RS232/LAN communication...
www.solarcontroller-inverter.com
 
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