Electric boat conversion - the generator

The photos show (1) the generator top view - it's very densely packed with equipment!... and (2) with the sound-proofing cocoon fitted.

In my researches, it became almost immediately apparent that only Fischer-Panda supplied suitable generators for our conversion - because only they have a range including a choice of (nominal) DC outputs, including the (nominal) 72V of our drive motor (and therefore, drive battery pack.) To have had a system that needed to convert voltages would have been very complex with a need for extremely high-current voltage conversion - basically, not practical with a motor drawing up to 200A... and a recharging current of up to 70A.

From my calculations - and other advice - it seemed unlikely our average power consumption could possibly be more than 4kW... so I opted for a 6kW unit to have reserve.... just as well, because in fact the unit produces 4.9kW maximum - and a recharging current of 70A at that maximum.

I found out about F-P generators first by directly by emailing F-P... and, delightfully, one of their directors, Barry Fower, replied, quite rapidly, in person - and appeared to be intrigued by my plans and basically thought they should work OK, which was very encouraging.

When I later contacted Rupert Latham about an SEM motor (and its controls,) it turned out he could supply an F-P unit.... and even better, by the time we actually decided to go ahead with the conversion, by pure chance happened to have a slightly-used unit for sale - terrific saving in cost.

The units are, frankly, far more sophisticated than we really needed... but tried and tested, so worth the cost. They also come with a sound-proofing cacoon and "live" water-cooled exhaust, which makes the latter basically inaudible... although you can (and crucially) hear the water "sploshing" in the exhaust separator - and you can (of course) hear the generator running - and, indeed, it vibrates the boat perhaps slightly more than we'd hoped, although the effect is very minor. With hindsight perhaps we should have mounted the whole unit on its own rubber mounts (as well as the motor itself having internal mounts) ... although vertical spacing was pretty exact... the cacoon only just clears the sound-proofing under the deck boards above!

I hadn't actually initially intended that the generator should run at maximum output all the time, necessarily... but every extra amp re-charging means extra time free to run blissful "pure electric" ... and the unit seems quite happy - not labouring or straining - chuntering away giving a steady 70A.

The unit requires quite a bit of auxilliary equipment - most of which came with the unit - but fitting took quite some thought and "tweaking"....

The handbook that came with the unit didn't altogether help - it was really for a slightly different unit and was often hilariously... but also, misleadingly, at times.... translated from the original German....

I'd checked that the dimensions meant the (cocooned) unit could slot into our engine space through the existing deck supports without modification - and that the weight (in the mix) would mean overall ballasting was about OK. In discussing the conversion details with engineer Alan, he brilliantly came up with a plan meant the unit could be mounted centrally for maximum access with the propellor drive shaft below- see separate posting for plan.

Basic facts are:
The unit is a 6kW 72V with freshwater cooling, including exhaust
Size: (lbh): 520 x 470 x 580 mm or 20.5" x 18.5" x 23.5"
Weight: 130 kg (286 lb)
Engineering contact: Chris Baker of F-P, email chris.baker@fischerpanda.co.uk

The fitting involved various slight problems - or at least things to be considered - where Chris Baker was invaluable with his advice... although I have to confess I adjusted some things according to my own decisions and, indeed, experiment! I've listed various points below, no particular order:

1. The unit requires an external fuel pump (although this was supplied with the unit.) Alan had some problems wiring this to switch on correctly - I'm not sure of the detail... but I think this was because the handbook was for a slightly different unit. (We used the existing boat's fuel tank)

2. The handbook outlines the cooling water intake plans for the two cases of (a) generator above the waterline and (b) below ditto... but not for "half-below" - our case! In fact the advice was to treat it as "below". This meant that the cooling water intake had to have external pipes fitted to a siphon-break device (which we had to buy) to avoid water being siphoned "backwards" out of the unit when it was switched off and the water pump - "impeller" - had stopped. The siphon break had to be fitted well above the unit - above deck - we found a convenient spot beside the "control box" - where the drive motor speed control was fitted - in a standard Morse control position.

Fitting these pipes was not altogether straightforward on our "used"/older model - newer units have a small loop of pipe that comes out through the cocoon that you remove and fit "feeds" to a siphon break if required, but in our case Alan had to break into internal (flexible) piping and make suitable holes in the cocoon.

The siphon break device has an automatic valve - we certainly need it - you can hearing it "popping" to let in air and break siphon effects!

3. The cooling system means the raw water drawn in cools an internal water+anti-freeze cooling circuit via a heat exchanger. But this system requires a "header tank"/reservoir well above the unit. The unit came with a crude (small) plastic reservoir and narrow bore plastic piping which Alan replaced with his own piping - again requiring a hole in the cocoon - leading to a metal tank he created beside our gas-cylinder box - you can see the yellow flexible pipe in the top photo above.

If the motor overheats until the coolant boils ... and, yes, we had that happen just the once! - the effect of Alan's yellow pipe is totally startling... being such a long fine pipe the bubbles coming through create an ear-shattering loud crackling noise... this all came about thanks to an intake blockage and consequent failure of the impeller.

4. The cooling water intake comes in via a filter, external to the unit. This has to be above water level to avoid any risk one floods the boat for opening it to clear debris! Contrariwise, there is a catch to this, the lid must seal air-tight after cleaning... but you have to be very careful this seal is made or if water is NOT sucked in within a short time (even 30 seconds matters) the engine starts to overheat. I think my failure to make sure of this led to the one time we had a drastic overheat. Interestingly, the initial reason I realised the intake had gone seriously wrong was that I suddenly realised I could hear the exhaust "popping" when I went ashore to work a lock. Our exhaust didn't "pop" normally.....

This water intake is a weak point in the system. Especially on the canal, the intake can very easily become blocked... and, with hindsight, our intake should not have been mounted on the starboard side meaning it gets terribly close to the bottom and edge of the canal if passing a boat(!) My solution is very simple - never turn on the generator if the canal looks full of debris, even to simply turn it off right there and then if you can tell you are about to have close to the bank (and possibly aground) ... so, in many ways it's not a major problem, but you do need to operate sensibly to avoid potential blockage.

I'd been warned the impeller might need replacing after a blockage and so bought spares ahead. What I hadn't really taken into account was that to refit a new one would be so tricky. Where the major problem was access to unscrew the cover on the pump - two flexible cooling pipes pass right in front... one, intake water, so safe enough to remove. The other, internal coolant, so disconnection would mean anti-freeze everywhere and a whole procedure to re-charge without airlocks.....

But the worst thing was that the retaining bolts were ordinary "slot head" and without an obstruction tool almost impossible to unscrew without damaging the slots. I've since obtained hexagonal-head bolts can be unscrewed (or refitted) with a side-access, ratcheted, box spanner.

Overall, I managed the replacement and it's worked perfectly ever since, but I would recommend one replaces the retaining bolts with hexagonal head before the unit is even put in place to ease replacement of this rather fragile impeller.

I have been advised, incidentally, that the whole pump can need replacing due to the abrasive nature of canal silt... which would not be an easy task and so I wondered about an electrical substitute.... not simple, it turned out... if the electric pump ran after the motor had stopped, cooling exhaust water would be sucked back into the actual cylinders of the motor causing, of course, almost total damage!!!

Being me, I decided that the real answer was that this fragile impeller should feed water to silence the exhaust (where failure would merely mean a temporarily loud exhaust) whilst the actual engine cooling was done by something less fragile.

I had no reply from F-P when I asked how easy (or not) it might be to separate the exhaust-silencing water system from the engine-cooling system. I may yet find a way to do that... who knows?

5. The engine cooling system has yet another problem. Because the unit is mounted in a sound-proofing cocoon, this is also a thermally insulating cocoon. And because the cooling stops the moment you stop the generator, heat generated quietly spreads after switch off...

But the unit has masses of safety cut-out devices, especially for over-temperature. So I slowly discovered it would fail to re-start immediatly after a burst of recharging because it "thought" it was too hot. To be honest, in normal daylight the indicator on the control panel is so dull I hadn't noticed it... I'd merely discovered that for trying to restart several times it was suddenly OK....

Penny only dropped when I suddenly did notice the indicator.... and fairly rapidly realised the problem... cut-out wouldn't let me restart when what was needed was that the engine ran to cool itself..... trying to restart turned the indicator off because, after about four attempts, enough cooling water had come in.... obviously daft catch-22, it must be possible to "tell" the system to run itself to cool off enough to be OK....

I eventually found in the hand-book this problem had been considered and there was an override button. IN the unit, INSIDE the sound-proofing... lordy, to operate that would be so non-pragmatic, I'd have to lift the deck boards, undo the cocoon, find the...

But, in any case, it turned out our unit didn't have that button! But I did have a circuit diagram so knew which terminals it was supposed to connect across... sure enough, connect those, the start solenoid (visible in the photo above) shot across and the fuel pump came on although something in the control panel made the most awful buzz...

I asked Chris (email) about that, he said it sounded like a relay chattering and it worried him. Fair enough, it worried me. He also said the trick was to run the generator on no load for about five minutes before switching off to let it cool.... didn't say how on earth I was supposed to run it on no load when just everything had dire warnings it must not be disconnected from the batteries it should be charging....

Ah well. I know about relays "chattering" for having too high current... so I added a resistors experimentally until the relay didn't chatter but the start solenoid still clicked over. And a switch on the control panel... tiny thing. If you want to restart the generator when it's hot because it needs to run to cool itself... hold the sprung switch .....

6. The unit comes with an external electronic "VCS" (voltage control system) unit. In the case of our second-hand unit this either arrived faulty or Alan mis-wired it and blew it or Alan mis-wired it (it certainly wasn't doing the right job) and I blew something trying to work out what was going on. But the importance of this unit and what it does is something needs a separate posting. For this posting, about the generator, I'll simply say that that I was advised that a common way to avoid the "ghost" over-heating problem was to run the generator "off load" for about 5 minutes before actually switching it off.

This may sound a simple instruction, but this advice completely contradicted other advice that the generator must never be disconnected from the batteries it was charging (if running) without risk of damaging its coils and output diodes. To go "off load" what one needed to do was SLOW the generator until it was not providing any current, you must not literally disconnect it. I could adapt my VCS to do this by (yet another!) added little switch. So you hit this switch, the generator slows, run like that for about five minutes, the unit is cooled enough not to register overheated condition when you next want to start.

Sounds simple, but there can be reasons you must stop the generator almost immediately - for example suddenly spotting debris in the water would almost certainly block the cooling intake. Or, it's time to enter a river lock, generator can't be on. Or you just don't want the generator on that moment!....

This doesn't actually matter, you can use the over-ride switch described in (5) above. But to cool by slowing the motor is less likely to build up strains so if one has time it's better to use this method - you can survive by over-riding, but you are at risk of running things too hot - and also the risk that the overheating was for a different reason (such as the impeller failing) so using the over-ride switch must be done quite carefully and watching to see that the over-heat indicator goes off after about 20 seconds... much longer and there may be a problem needs different consideration. Therefore, cooling by slowing is safer and better. And the over-ride switch must be sprung so there is absolutely no risk you over-ride the temperature safety device when it may be indicating a catastrophic fault without you realising. By having a sprung switch, you are consciously over-riding for this one specific condition that upon re-start it can take about 20 seconds for the unit to pump enough water to cool the unit to working temperature.

Further details - especially the VCS - in other postings.