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MoominPapa last won the day on January 23 2017

MoominPapa had the most liked content!

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About MoominPapa

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  1. MoominPapa

    Lithium battery project.

    I forgot in my previous reply to add that 4000 series CMOS (at least the ones I'm using) are specced to power voltage from low all the way to 20v, so there's no need to have a voltage regulator for this part of the circuit, just an 18v zener to do last ditch spike chopping. The Arduino comes with a series regulator that always costs some juice. I'm replacing that with a 12v - 5v switching module, but it's still a parasitic load. The Atmel processors in the Arduino need 3.3 - 5v, I think. I guess smaller microconrollers will have a larger range. MP.
  2. MoominPapa

    Lithium battery project.

    That's about the one source I've not looked at. I hate getting technical information from videos: a written document is much better. Best source I've found is this: http://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/ MP.
  3. MoominPapa

    Lithium battery project.

    The main microcontroller in the Arduino is going to have quite a lot of "stuff" around it like displays and i2c bus drivers, so I couldn't be certain that I would get the power consumption down far enough to be safe when the lithium system is isolated for some time. For instance when the boat is unoccupied or over the winter, when the lithium pack will be discharged to the idea storage state of 30%-50% and then isolated, leaving the boat running off the engine start battery floated by the AC charger. Parasitic loads in that state when the pack is unmonitored could drop one or more cells below the lower voltage limit which would be a disaster. A dedicated 8-pin PIC would be a good alternative. I went the way I did because I could be sure a priori of making a design that would work. I don't have much experience of very-low-power microcontroller use. I'm not engineering here: the prototype is also the product, so something that works as designed first time is good. I slightly regret using sockets, it would have been fine without, in retrospect. The rest of the electronics will not be socketed. No problems with transients in testing. The power consumption of everything other than the relay coils is so tiny that the rail can be decoupled with large-R large-C filter. There's a 0.1uF ceramic across the electrolytic too, to handle fast transients. MP. ETA. The 8-pin chip visible on the board is an optocoupler on the incoming control signals, to make absolutely certain that the power domains are isolated, and power can't leak from this circuit to the Arduino when the Arduino is off.
  4. MoominPapa

    Lithium battery project.

    My winter project is to install a LiFePO4 domestic battery bank, and design and build the control system for same. The architecture will be that all the charge sources (alternator, charger and solar) and all the loads are permanently connected to the engine start battery, which will remain as conventional lead-acid. The lithium bank will connected to this via a contactor controlled by the BMS, allowing charge and discharge termination and emergency disconnect if enough unbalance builds up to take a cell out of the safe voltage range. I decided that I'd rather risk a flat start battery on lithium low-charge disconnect then have all the lights go out without warning. The BMS will sound an alarm when it disconnects the lithium bank. Having the start battery always in circuit means I don't have to worry about alternator load-dump. The BMS will be Arduino based, with a dedicated TI analog front-end chip for reading the cell voltages and pack current from a shunt. Today I completed the first module, see photo below. The black box is a Tycho 250A magnetic latched relay. It uses no power when in connected or disconnected state, there are two coils which are pulsed to open or close the contacts. The control board is 4000 series CMOS logic and draws about 50 micro-amps when idle. This is important, as it will be connected direct (fused) to the lithium bank at all times. The logic generates 15mS open and close pulses for the relay coils, switched by MOSFETs. There are two input signals from the computer. One opens the relay, and is conventional. The other closes the relay and is fail safe. The pulse has to repeated every second or so, or the logic will time out and open the relay. That's so if the Arduino fails, or crashes, or isn't running a valid program, or is powered down, this module automatically ensures that the lithium bank is isolated. Next stage is the Ardunio hardware, which consists of a 128Kbyte EEPROM for logging, the TI analog front end, and an interface to a small OLED display. Logs of all parameters at second resolution for several weeks will be stored and transferred to my laptop over USB for diagnostics. I have some 3.3Ah Lithium cells on order for doing the development, they are cheap enough to be able to do damaging tests, and small enough to use a 21W brake-light bulb as a load-bank and bench PSU as a charge source. Final bank will probably be eight 180AH CALB prismatic cells connected 2P-4S to give 360AH at 12V. MP.
  5. MoominPapa

    Cheap Electrical Monitoring

    Have they never heard of negative numbers? MP.
  6. MoominPapa

    Found in the dry dock.

    That' not a skeg, it's a bridge-beam! A long skeg does provide a location for the occasional tree branch to jam between the rudder and the skeg. It's a bit disconcerting when the rudder refuses to swing in one direction, until you learn to momentarily push it the other way to release the interloper. MP
  7. MoominPapa

    Found in the dry dock.

    Prove it!!!
  8. MoominPapa

    Found in the dry dock.

    Just dried out in the Excellent Langley Mill Boatyard drydock, and look what I found attached to the top of the skeg. If it's not obvious, it's a "fishing" magnet, with a stub of rope left attached. It's not mine, and I have no idea where it came from. There's been the odd clonk from the rudder, which I attributed to wear in the bottom bearing, but it seems more likely that it's from this. Don't go magnet fishing around steel boats, people, they will steal your magnet. MP
  9. Does it have a mural of Lemmy on the outside, per chance? MP.
  10. MoominPapa

    A warning to others...

    Very troo, that. MP.
  11. MoominPapa

    A warning to others...

    The hole in a skin fitting is often quite small. The result of trying to share the waste plumbing for a sink with a pumped source like a washing machine is normally that the washing machine water backflows into the sink. Adding a dedicated skin fitting was the right think to do. MP.
  12. MoominPapa

    Cointra water heater - should I get one?

    The new one appears to be made in Italy. MP.
  13. MoominPapa

    Cointra water heater - should I get one?

    Looks fine, as long as the importers can legally sell a CE approved appliance after Match next year, of course. MP.
  14. MoominPapa

    Cointra water heater - should I get one?

    No. I think I read it on here, but I can't remember for sure, sorry. MP.
  15. MoominPapa

    Cointra water heater - should I get one?

    I thought the Morco factory had a reprieve, and was producing again? MP.

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