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Craig Shelley

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  • Gender
    Male
  • Location
    Birmingham

Previous Fields

  • Occupation
    Engineer
  • Boat Name
    Pretty Amazing Grace
  • Boat Location
    here and there

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  1. Before it went offline, the Willington gauge prediction was showing a bit of a bump. See attachment We're moored on the pontoon at trent lock, and there are a couple of narrowboats before the floodgates on the cranfleet cut which have started to break free from their moorings. One is currently on the towpath facing the opposite direction - the owner is aware. The other also appears to have broken free at one end, but we haven't seen the owner yet. Access is currently a little awkward due to the water level.
  2. On Monday morning (4th Nov), my father was approaching bridge 55 on the Trent and Mersey, and was told by walkers on the tow path to be careful as another narrowboat had come adrift near the bridge. CRT staff boarded the boat as he was passing it, and were securing it to the bank. Unusually, the front doors on the boat were open and there was no front mooring line. Today while we were out walking (different location) my father recognised the same boat and ended up chatting to the owner. It turns out it had been broken into, and ransacked. Among other things, domestic & starter batteries, tiller, windlasses, and mooring lines had been stolen. The owner had left boat quite substantially and visibly secured, and would have required a determined effort to break in.
  3. Just catching up on the past few days of messages. I'd advise at least having a panel voltage meter with 3 decimal places of precision. Over time you develop a "feel" for the state of charge based upon the voltage. In our system, we had no bms or cell level monitoring. In the early days, we didn't know what limits to work to, and had very little instrumentation, no ammeters etc... The measured voltage predominantly depends on two things; state of charge and load/charging current. When the batteries are in a rested state I.e. Very little load/charging current for a couple of hours or so, the voltage is a very accurate indicator of state of charge. For us, 13.330V fully charged 13.200V middle ish. 13.100V middle to low, 13.000V we try to avoid going too much lower than this. At either end of the charge curve, you notice the voltage fluctuates much more. For the first few months after installation, we kept the voltage around the 13.2V region. As we later installed the various safety systems, we became a little more adventurous, and carefully explored the upper and lower ends of the characteristic. While charging, the measured voltage will be higher than the resting voltage, and will depend on the charging current and state of charge. Annoyingly, charging current depends to a certain extent on alternator RPM. During the middle three quarters of the capacity curve, the voltage doesn't change a great deal as the batteries are charged. For example if the alternator is kicking out 80A, at about 50% SOC we might see ~13.6xxV for well over an hour. This is where the extra decimal places on the meter really help. The numbers will slowly be counting up as the batteries charge e.g. 13.614 ... 13.615 etc... You get a good feel for the rate of charge. When approaching about 80% (what we call full), the voltage starts to rise quite rapidly. The last decimal place becomes a bit irrelevant at this point because of the speed the voltage is moving. At somewhere between 13.9 and 14.0V, we cut the alternator field and charging stops. The battery voltage rapidly drops to say 13.4xxV. It then takes an hour or so, depending on load current, for the voltage to settle out at the resting voltage value. When choosing a voltage to cut the alternator off at, we were initially very over cautious. The problem with setting it too low e.g.13.7V is that the dependence of charge current on engine RPM means that while traveling, revving the engine might cause the current to ramp up momentarily. This causes the measured voltage to increase, and hence lead to premature tripping. As we got more accustomed, and understood what was happening, the trip threshold was gradually increased. We're now quite happy with a value around 13.95V. Providing the alternator is supplying sufficient current, the voltage does not remain at this high value for any significant length of time. Once the voltage has passed about 13.7V, it really does start to rise quite quickly, accelerating as it goes. The alternator cut off threshold is then tripped cleanly and is far less susceptible to premature triggering. This strategy gives a clean cut off at a consistent state of charge. It would be nice to either control the alternator current to a set value, or compensate for its variation using a software battery model. To summarise; the measured voltage is mainly determined by the battery, which is predominantly dependant on state of charge and load / charging current. With LA batteries, the alternator is required to regulate the voltage while the battery absorbs the energy. In my opinion an alternator voltage regulator is not needed for lithium unless you wish to either fully charge the batteries to 100% using CI/CV mode, or wish to regulate alternator temperature/engine load, or if the alternator current rating is too high for the capacity of the battery pack.
  4. The fuse in the +ve is 250A to the motor controller. The fuses in the +ve and -ve charge cables are 50A. The charge cables are 10mm2, and route through the cabin. The negative terminates at the busbar. The +ve goes via a charge relay contact to the starter alternator. If "somehow" the +ve bow thruster battery terminal were to be shorted to the hull, the fault current would circulate via the hull and engine to the negative busbar, then back along the charging cable -ve to the bow thruster battery. Without a fuse in the -ve there is a possibility that the -ve charge cable might burn up. At 10mm2 I'm doubtful it would go that far, but the cable does run through the cabin. There's no harm in fusing it close to the battery.
  5. Very good point. Engine to hull would certainly be a much better place for a bonding point. Also often overlooked is fusing the negative charging wire to bow thruster batteries, in case of short from +ve to hull at the battery.
  6. Sorry, there's an error in my original post. The prop shaft actually has a flexible coupling, which is electrically isolating it. The prop shaft at the seal is at about +0.5V from the hull. I imagine this is due to the metal the prop is made from. The lost return current can be measured at the engine -ve wire so it must therefore be returning via some other route on the engine e.g. exhaust.
  7. Thanks for the quick reply. Would this work for powered DAB aerial? The aerial has two coax cables, and an amplifier power supply wire. The DAB coax is terminated with SMA/SMB connectors.
  8. Yesterday, while tidying up some cabling, we discovered the current supply to the radio is higher than its current return. Current supply: ~1A Current return: ~400mA The remainder has been traced to be going down the aerial cable screen to the hull, and then back to battery negative via the engine . This may be unrelated, but when we recently serviced the prop shaft seal and discovered one of the brass components was bright green and pitted, indicating galvanic corrosion. Currently, there is no bonding from battery negative bus bar to the hull. I'm going to install a bond wire with sufficient captivity to handle parasitic and fault currents. It makes a lot of sense to have a bond wire from the negative bus bar to the hull. There is another forum thread which discusses the need for a bond wire in detail. The supply to the radio is shared for TV, and several cigarette lighter sockets. A percentage of the current from these devices is also returning via the radio. Does anyone have any suggestions to prevent current escaping to the hull via the radio aerial?
  9. Snap! Same person. He was very helpful, and even made us the cabling and connectors.
  10. I guess he got the wrong end of the stick when his doctor prescribed Lithium.
  11. Sorry, I was being a little metaphorical. The "pressing of a button" implied taking a manual action such as operating a switch on the dash board. This might be done after engine start, but ultimately, the decision of whether or not to run the alternator is with the helmsman.
  12. Agreed 100%. It really isn't too onerous to press a button when you decide to charge up. A simple cut-off when a pre-set voltage is reached is adequate. It's also useful to be able to manually turn off the alternator when for example, you find yourself going against the flow on a river and wish to shed some load from the engine to help keep the temperature down. While travelling, having the domestic loads supplied by the batteries after the alternator has "cut-out" really isn't an issue either, just a different way of thinking compared to LA. The easiest and safest way of shutting down the alternator is to de-energise the field as is a relatively low current and trivial to switch with a standard automotive relay.
  13. The instructions for this module are a little lacking, so some time back I wrote these notes: long press set: output logic invert (can only be done if input voltage is not in hysteresis band) enter - toggle between displays: 1 Live Voltage 2 Minutes output has been on for Set key steps through settings: 1 Voltage measuremet 2 Upper voltage, above this relay will turn on 3 Lower voltage, below this relay will turn off (this cannot be higher than Upper voltage) 4 calibration +/- 0.5V 5 dl display shutdown delay in minutes Input pins (top right): When input is active, relay will come on irrespective of invert setting Jumper configures: Short to activate External 5V to activate Notes: At power on, output will always be off. At power on, if voltage is in hysteresis band, it will default to off. Hysteresis band can be configured so that output behaves like a triggered latch by setting one of the thresholds to an unrealistic value Crossing a threshold occurs when voltage has passed through the threshold and next digit is displayed i.e if lower threshold is set to 12.0, then the switch will operate at the boundary between 11.9 and 12.0 if upper thershold is set to 12.0, then the switch will operate at the boundare between 12.0 and 12.1 Power Consumption: 18.67mA relay off 49.5mA relay on 8mA display removed 39.6mA Relay on and display removed 15-20mA from 5V (output of regulator display dependent) 7mA from output of regulator with no display
  14. I think it still ought to be doable. MOSFETs are now down to below 500uOhms Rdson. Several in parallel would be needed for 3kw, but still cheaper than a motorised, or latching switch.
  15. Are there any solid state solutions to this available yet? Should be a lot cheaper and simpler than latching or motorised switches, in theory. Would still want to have a proper switch for manual isolation though.
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