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Powering a 8KW motor from a generator


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This thread may be of help http://www.canalworld.net/forums/index.php?showtopic=89095

 

Unless its a very small boat 800w will be nowhere near.

We've just completed conversion of Sara to electric drive and did a week of 'sea trials' in October, these details may help:

 

Sara is an Ijselaak, with a 'proper' boat shape, not a flat bottom and blunt ends. She is 14.1 metres long and 3.5 metres beam.

Calculated hull speed is about 8mph.

 

Propulsion system is:

Four 10Kw 48v DC Lynch motors, mounted in a frame with reduction kevlar belt drives onto a single shaft.

Four 300amp 48volt 4QD motor controllers paralleled up to one joystick controller.

Traction battery bank giving 825 AH at 48 volts.

13KW 48 volt DC Fischer Panda cocooned generator.

Two paralleled Victron Combi inverter chargers giving 70amps charging at 48 volts and 6KW of 240v AC for domestic use.

 

Much to my relief the sea trials confirmed my design calcs almost spot on:

Cruising at 3mph takes about 60amps, i.e. around 3KW.

Cruising at around 4.5mph (Aire and Calder - so that is allowed!) consumes about 110 amps, ie around 5KW.

Going up to 6mph increased the consumption to about 350 amps, ie 17.5KW.

Bursts of 'full throttle' take consumption up to over 600 amps.

 

So at normal cruising speed our battery bank will support about 6 hours cruising before we have to either start the generator or return to a shore line. At higher speeds, e.g. for river work, we would start the generator straight away.

At 6mph, assuming full batteries, with the generator running, we have about 5 hours before we have to reduce speed.

I wouldn't want much less generator capacity than the 13KW otherwise the ability to do, say, the tidal Trent would be compromised.

 

Cruising without the generator running, particularly as Sara produces very litle wash, is very quiet - we have a stealth barge!

 

HTH

 

John

MV Sara.

Edited by Robbo
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on a much smaller scale, I have a 16ft camping cruiser with 4x100W solar panels and 4x110AH batteries powering a 32lb minn kota outboard which draws about 30A at 12V.

 

there is an auxiliary Evinrude 4HP 2 stroke.

 

when cruising on the Thames I try to moor up overnight at the EA charging points that are provided at some locks principally for the use of electrically propelled boats; a 20A charger tops up the batteries in about 12 hours.

 

on a sunny day I can quietly cruise for about 6 hours at walking speed.

 

the pleasure that comes from silent cruising more than compensates for any lack of speed; the only sound is a gentle throbbing from the propeller.

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Surely, Lynch could advise? I'm sure a soft-start would be possible in which case you would not need an engine of much more than 8kW. You'd probably not want to run an engine at its MCR all day. An 8kW motor is going to limit the top speed a bit.

 

Has anyone rented the all-electric boats on the Mon & Brec?

 

 

8kW is about 11hp, to put it into perspective...

Edited by Mike the Boilerman
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8kW is about 11 bhp which seems a bit meagre. But my last cruise ship, which weighed about 30,000 tonnes and had a propulsion power of 2 x 14,000kW, would only consume about 500kW when moving at about three knots. Propulsion power is proportional to speed cubed. So halving your speed uses one-eighth the power.

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Thanks for the replies, I'm not opposed to the battery idea was just considering my options, lynch have some case studies on their website and have replaced a 47ft trip boat that had a 55hp BMc commodore with their 8KW motor. Which is why I thought it would be enough power.

 

Does anybody have an idea on what sort of battery bank size I would need ?

 

http://www.lynchmotors.co.uk/green-marine/electric-vehicle_motors.html

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This is basically "series hybrid". If it can be made to work, then there's advantages of running the engine when you want; and running the propulsion motor at slightly different times - using batteries to fill in the gap. Of course, doing so would reduce efficiency, but there are advantages and disadvantages. Also the location of the engine/generator can be different - for example it could be installed transversely; or at the front.

 

Basically, its an alternate type of transmission system.

 

I suspect the main issue will be that its so uncommon, you'd need to cobble together from various parts some kind of control system, and if it was a "manual" control thing then you could end up leaving yourself stranded with not enough power at a (possibly critical) time and need to wait for the generator to kick in; or develop some kind of bespoke automated control system that monitored the batteries and charging (topic in itself!).

 

It would be interesting to try out though.


ETA if you do try it, try to find and use a generator that can have a hot water circuit added/adapted to it, for the calorifier etc.

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You will suffer the inefficiencies of both the generator and the electric motor, offset to a degree by being able to run the diesel engine at its most optimum speed.

 

Overall, compared to a standard diesel engine & gearbox installation, I think it will cost more, use more fuel and be much more difficult to find boatyards capable of repairing it when it goes wrong.

  • Greenie 1
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...Has anyone rented the all-electric boats on the Mon & Brec?

Yes. Never again.

A complete overnight charge was required every night.

The proprietor assured us that they were ample recharging points available along the route. They were not - we lost whole days because the ones at our night stop were all in use.

That was some years ago so I expect the provision is now better, but I will never ever rely on electric points for propulsion again.

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Yes. Never again.

A complete overnight charge was required every night.

The proprietor assured us that they were ample recharging points available along the route. They were not - we lost whole days because the ones at our night stop were all in use.

That was some years ago so I expect the provision is now better, but I will never ever rely on electric points for propulsion again.

You'd think they would plan this better with dedicated points for each boat! Thanks for the feedback. When running, what did you think of the boat's performance?

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You'd think they would plan this better with dedicated points for each boat! Thanks for the feedback. When running, what did you think of the boat's performance?

I don't remember - which means it wasn't exceptionally good or exceptionally bad. We weren't in any hurry and with 3 children so I can't offer any useful comment.

ETA

with 3 children? It was a long time ago! The youngest is now 35! It is remarkable how strong the memory of that discomfort still is!

Edited by system 4-50
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The article seems to assume that batteries charge in a linear manner, this is most definitely nothe he case.

 

"At idling speed this would take 12 hours to charge the battery (12 hours x 30 Amps = 360 Units) and at full cruising speed it would take just over 6½ hours (6.67 hours x 54 amps = 360 Units). In practice the engine speed is frequently varied and the real answer will be somewhere between these figures depending on just what we are doing."

 

Edited to unmangle the effects of the autowrong spellchecker.

Edited by cuthound
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If you go back to the OP's original question, he want's to run the motor directly from a generator not via a battery.

 

Exactly but his proposal amounts to a fruitless re-invention of the wheel. What has been suggested is a proven alternative that still utilises a generator powering an electric propulsion motor, but in the most efficient manner.

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The article see s to assume that batteries charge in a little are manner, this is most definitely nothe he case.

 

"At idling speed this would take 12 hours to charge the battery (12 hours x 30 Amps = 360 Units) and at full cruising speed it would take just over 6½ hours (6.67 hours x 54 amps = 360 Units). In practice the engine speed is frequently varied and the real answer will be somewhere between these figures depending on just what we are doing."

As far as I could make out they'd only done three trips when they wrote that article. Shortly thereafter they would no doubt have discovered that they were severely under-charging the batteries.

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Surely it depends on the controller plus how often it would be at max power?

 

I would suggest that it depends on the initial draw of the 8Kw unit on start up. A lot of electrical units draw much more than they're rated at on start up, that's why you tend to need more available power than you think.

 

There are members on here who can give you chapter & verse a helluva lot better than I can!

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I would suggest that it depends on the initial draw of the 8Kw unit on start up.

I've never used one but my understanding is that all that stuff is handled by the controller (which can cost as much as the motor!)

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I've never used one but my understanding is that all that stuff is handled by the controller (which can cost as much as the motor!)

it should be... but that doesn't help at all if the power source cannot supply the power needed by the controller.

 

startup demands can be massive (many times the normal running power), as an example I used to work with a motor that in was rated at 800w (or around 3A @ 240v) however the power needed when you hit the start button would trip out a 32A supply 5% of the time, a clamp meter on it's power lead showed a peak demand approaching 60A.

 

if that load scaled up in a similar way with a lynch motor then an 8kw motor may impose a demand of 160kw for a very brief period (fractions of a second)

Edited by Jess--
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as pointed out earlier, in the case of a motor starting up on no load, this is not necessarily the case.

 

however in the case of an electric drive motor which has no clutch or gearbox, it will always be under some load whenever it starts, including going from forward to reverse.

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Only just noticed this thread. I've been taking an interest in electric propulsion lately. I'm only just in the process of ordering the shell so can't speak from experience but I have been in touch with some suppliers. When I spoke to Lynch I was recommended this set-up. The 16 V Twin was £7500 inc VAT for the kit which rather stopped me in my tracks. It seems the Americans are well ahead in electric drive and there's a lot more choice over there. I've been looking at Thunderstruck kits which are more in my comfort zone. It's true that the controller is the greater part of the cost. The motor itself is relatively cheap, which made me wonder if a single controller and two motors might be the way to go. I need to look into that further. Not sure about the legal requirements but it would seem pretty obvious that if there's gas on board the motors should be brushless.

 

Personally, I'm planning to have sixteen 110Ah AGM batteries (48v) and probably start with a 1200w solar array and up it to 1600w if needed. The guy from Lynch seemed to think this was an absurdly high amount but it's principally for off-grid living. Winter cruising will be limited so I don't anticipate charging problems and there will be a back up generator anyway. I think there should be enough excess in the lighter months to feed a dump load immersion heater in the calorifier and save on gas. My hope is to do the full system (solar / batteries / motors / controllers / cables / fuses / monitors etc.) for around £8000 which I think would be good. Considering the amount of space freed up in the living area through lack of engine room, I'm surprised it's not a more popular option with those less inclined towards the traditional aspects of boating.

Edited by stegra
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Only just noticed this thread. I've been taking an interest in electric propulsion lately. I'm only just in the process of ordering the shell so can't speak from experience but I have been in touch with some suppliers. When I spoke to Lynch I was recommended this set-up. The 16 V Twin was £7500 inc VAT for the kit which rather stopped me in my tracks. It seems the Americans are well ahead in electric drive and there's a lot more choice over there. I've been looking at Swordfish kits which are more in my comfort zone. It's true that the controller is the greater part of the cost. The motor itself is relatively cheap, which made me wonder if a single controller and two motors might be the way to go. I need to look into that further. Not sure about the legal requirements but it would seem pretty obvious that if there's gas on board the motors should be brushless.

 

Personally, I'm planning to have sixteen 110Ah AGM batteries (48v) and probably start with a 1200w solar array and up it to 1600w if needed. The guy from Lynch seemed to think this was an absurdly high amount but it's principally for off-grid living. Winter cruising will be limited so I don't anticipate charging problems and there will be a back up generator anyway. I think there should be enough excess in the lighter months to feed a dump load immersion heater in the calorifier and save on gas. My hope is to do the full system (solar / batteries / motors / controllers / cables / fuses / monitors etc.) for around £8000 which I think would be good. Considering the amount of space freed up in the living area through lack of engine room, I'm surprised it's not a more popular option with those less inclined towards the traditional aspects of boating.

 

Purely on the charging side, I make it that you'll have 10.5kWh usable power from your batteries before they'll be down to 50%. (4 banks of 4 x 110Ah 12V batteries giving 440Ah @ 48V.) If my maths are right then there is absolutely no way you'll replenish that with only 1600W of solar.Not even in high summer.

 

I'm also at a loss as to how 10.5kWh will power a 12.5kW motor for any length of time.

 

I must be missing something.

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I think your costing may be a little 'on the optimistic side'.

 

110Ah 12v AGM batteries £184 each, so 16 of = £2944

http://www.sunshinesolar.co.uk/prodshow/_110AH_12V_AGM_Deep_Cycling_Sealed_Battery/AGM110.html?gclid=CjwKEAiA-rfDBRDeyOybg8jd2U4SJAAoE5Xq0UdBDplcB4i33JDCxD6c61yKOzAe5DsYgULSV4KTaRoCExzw_wcB

 

'Cheap' solar panels are available at around £1 per watt, but suggested for 'liveaboard usage' is this

http://www.sunshinesolar.co.uk/prodshow/Sunshine_Polycrystalline_250W_Solar_PV_Module/REN250W.html

 

at £377 for 250 watts, 6 of these (1500w) will cost £2262

 

Lets add in another £600 + for a 60A MPPT controller.

 

Total so far (for batteries and solar panels) = £5806, leaving £2000 for the motor, controllers, cabling etc etc etc.

 

If you are going to 'do it' then cutting corners using 'cheap' components (batteries etc) is not going to work.

 

I would suggest that for most of the year you will be spending more on fuel to run the generator than you would with a conventional engine, gearbox and shaft.

As noted above, the solar is unlikely run / power the motor and 'liveaboard' usage.

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Purely on the charging side, I make it that you'll have 10.5kWh usable power from your batteries before they'll be down to 50%. (4 banks of 4 x 110Ah 12V batteries giving 440Ah @ 48V.) If my maths are right then there is absolutely no way you'll replenish that with only 1600W of solar.Not even in high summer.

 

I'm also at a loss as to how 10.5kWh will power a 12.5kW motor for any length of time.

 

I must be missing something.

Admittedly, using those figures is looks unlikely. When I spoke to Lynch who have installed working systems about their 16kW system, I was assured the battery capacity was more than ample. I didn't really do the calculations; the boat is primarily a live-aboard. I would have to assume that the motor runs at less than its constant power rating. Watching YouTube clips of working examples, mostly in America, there's generally several hours cruise time with smaller battery capacity. Obviously, speed is important because of the cubed rule. I don't know how much hp a diesel engine would provide at the prop to keep to a steady 3-4mph. Perhaps that would give an indication. There are electric narrowboats that are intended to cruise long hours and be grid-charged overnight. Does anyone know the battery capacity of these? I'm not averse to increasing the battery and solar.

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