dmr

I also have failed with the www. In my model of the universe most chemical reactions get more lively with temperature. So I can see that we might need to charge a cold battery harder to get the reaction going, but conversely I would expect a hot battery to make more voltage on discharge. But maybe the reaction has to be endothermic one way and exothermic the other ????? (always preferred physics to chemistry at skool) ...........Dave

I will hopefully get a graph here later, it involves a bit of format conversion and messing about. My measurements today suggest that with a light load (5-7amps) the battery terminal voltage is at most 0.1 volts lower than the Trojan Voltage Curve With an 11 amp load its closer to 0.15 volts. The big unknown here is the temperature effect. Does the battery voltage do the same thing as the recommended charging voltage by unceasing at 30mV/degree? The batteries were only about 5 degreesC So if you really started out at 100% and took out 187Ah that would be 58% state of charge, giving about 12.23 volts "rested". If we take 0.1 to 0.15 volts off this for your load then that's 12.08-12.13 which is a fair bit higher than your figure of 11.67.. Do you measure your voltage at the battery or after an isolator/fuse etc? How cold were your batteries?. .............Dave

I imagine you have to hypothesise a "chemical battery" inside the actual battery and this has some voltage. The charge current is then the difference between the applied charge voltage and the "chemical" voltage, divided by the total internal resistance. A flat battery has a low voltage so will take a big charge current despite an extra bit of internal resistance. A charged battery has a high internal/chemical voltage so takes very little current despite a lower internal resistance.. This makes sense to me because when we first turn the charger off we actually see this higher voltage. ...............Dave

Interesting Link, I had not read that section before. I would hardly call that curve Linear!! Do you know if the off load terminal voltage of a battery will vary with temperature? or just the voltage required for charging???? ..............Dave

Yes, but you are obviously a skilled and competent person so must be worth at least £30/hour !!!!! I think I would be tempted to use a metal box for this cheap stuff just in case it bursts into flames???. I bought several of the Maplin units on a special offer for a silly price. But more significantly, the price of some of the electronics coming from China and Hong Kong and sold on eBay is unbelievable. How does anybody make a living (even in China) selling stuff for £1.50 with FREE postage to the UK???? I do hope that youngsters are taking advantage of the huge hobby potential of all this:, building electronics is now cheaper than taking drugs!!!!!! .............Dave

Its an interesting topic. The old Silver Maplin/Nikkai units run very cool so must be efficient, so I reckon these will be better than a dedicated small inverter. However if you use a lot of 12 volt stuff it MIGHT work out better to replace it with mains stuff and leave an inverter running. The inverter quiescent drain might be less of a loss than the power lost in the 12 volt cable runs?. We have loads of chargers plugged in that just come alive when the engine runs (TravelPower). If I use the inverter I would need to turn all these off and then would forget to turn them back on, so I prefer to mostly use 12 volts. The trouble with this is that we have an increasing number of 12volt to USB chargers that get left on more than they should. Still diesel prices are predicted to be low for a few years and global warming might generate more solar power so maybe its not worth worrying.. ..........Dave

This look interesting (I actually bought the bigger version but have not got round to doing anything with it yet). Is it ok for radio interference and how hot does it run? Realistically by the time you have put it into a metal box with cables and connectors its going to cost more than the Maplin unit,but then DIY electronics is fun! You could build in a lower current version of this :... http://www.ebay.co.uk/itm/Dual-LED-Digital-Voltmeter-Ammeter-Amp-Volt-Meter-Current-Shunt-DC-100V-50A-/251628980037?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item3a96418745 and monitor the consumption of the laptop to optimise screen brightness against battery life!!!! I am thinking about an amp-hour counter based on an Arduino! .........Dave

Yes, but the OP has 4 Trojans and I have 4 Trojans so a measurement from me is probably better than something found on the www,.... as long as the op takes it for what it is, rather than a fundamental truth, Then again its somewhat cold here today and that may well be a bigger influence on battery voltage than the load effect. And there might be a dribble of solar going in and that's an unknown effect. Anyway, so far we are still in the 80% charge region and with a draw of between 0 and 5 amps I am seeing battery (terminal) voltages only about 0.1 volt below the published Trojan voltage curve. I am probably not going to get below about 60% today as I will do an engine run this evening to warm the back cabin and comfort takes priority over scientific experiments .............Dave

Iv'e never had any trouble with low battery volts and the Maplin converters (as in my post #9) I do have a good dedicated cable run from the switch panel to the "computer table", but then its a long boat, and I do sometimes take the batteries down to about 35% charge, so we get some low voltages. The inverter complains like hell! ...........Dave

or this one, which is a slightly higher power version of the one that Pete suggested......... http://www.ebay.co.uk/itm/NIKKAI-120-W-LAPTOP-CAR-POWER-SUPPLY-/281581375357?pt=UK_Computing_LaptopAccessories_PowerSupplies&hash=item418f8ecf7d You won't need the higher power but its nice to have some in reserve. I have found these even more reliable than the smaller ones, though the failures that I have had were probably self inflicted. Some of the little black ones (not all) make a lot of radio interference. Also the silver ones are good to 16v so will be ok if you do equalisation chargers. I think the smaller one is only spec'ed to 15v though mine do ok on 15.5 .............Dave

My figure above was a "guess" based on what I remember from looking at voltages a while ago. I have a smartgage and current measurement, and a set of 3 year old Trojans in good condition. I will try to measure a few numbers for you tomorrow, I am charging right now. ...........Dave a looking

Based on aiming to stay above about 50% charge I would aim for about 12.0 volts, If I was intending to go down to 20 or 30% soc, I would not rely on a loaded voltage measurement so I have not paid much attention in that region. .............Dave

Had an interesting conversation with a professional boater a few years ago on this subject and he said there would be very little demand for an advanced course, essentially because beginners would not do it and most experienced boaters, after just a few weeks of boating, honestly believe that they know everything there is to know. I think sadly there is some truth in his observation. ...........Dave

Just to elaborate on wot Nick has said, and without repeating the previous thread, this really is not the way to go. The only easy way to assess state of charge from voltage is to turn everything off and wait at least several minutes. This is not compatible with living on a boat. (I did it once and forgot to turn the fridge back on, big domestic trouble) Trying to get charge from LOADED voltage involves knowing the current and the internal resistance of the battery.This resistance is made up of the proper resistance of the metal bits, plus a sort of "electro-chemical" resistance which is complicated and variable. For example, if you have just done an equalisation it might be lowish. If you have not equalised for a while it will probably be increased due to the suplhate coating. As nick says it will probably also change with state of charge. Life is just too short to map this out for every condition, but an ex forum member did just this (and more) and built all this knowledge into his Smartgage I was a sceptic for many years, but I promise you it works! ...............Dave

I really don't worry too much about voltage during discharge, I have a Smartgage and although I accept its not perfect I believe what its telling me. Only real issue with deep discharges is that the inverter gets a bit stroppy, but we rarely use the inverter.anyway. Trojans are spec'ed to go down to 20%. The 50% rule is a good guide but gets taken much too seriously, especially on this forum! ...........Dave and some people (including Trojan???) say that continued very light discharge can be a BAD thing, I suspect 75% is ok but maybe 90 to 95 is not?. ............Dave

http://evbatterymonitoring.com/webhelp/section_3.htm see figure 18, not sure I believe it but its interesting. ..................Dave

Well, they have travelled all the way from America and maybe sat in a warehouse here for a while too. I purchased a new set of Numax a few years ago that were in a shocking state! There should be a date stamp on the Trojans somewhere. The www will tell you how to decode it. Its a good idea to give new batteries a good charge/equalise but this rarely gets a mention these days. dunno where you are but I bet you a pint an equalise will sort this out. ...........Dave..

You are most likely not charging the Trojans quite as much as you think and now have some sulphation. You need to have some means of doing an equalisation charge (15.5volts), this will sort them out (I was going to say this'll fix it but that phrase is non PC these days!). Don't worry so much about the 100% charge every other day, Trojans can take some abuse, a full charge once a week, or even less, will be fine as long as you can equalise once every month or two. If you have sulphation the capacity (and SG) just settles at a lower level so the battery shows the outward signs (tail current) of full charge but its not. SG should be similar to your starter battery, and the "green" SG of your starter confirms that your hydrometer is OKish Don't worry, after only a month you can easily sort this out. I suspect Trojans actually enjoy a really good discharge once in a while,.... take them down to 30! .............Dave

I have the cheap Sterling charger (Budget Pro???) for those rare occasions when we have shore power My observations suggest that it goes into float mode much too quickly, so if you get a touch of sulphation it may never recover and so let things go downhill very quickly. Hopefully his more expensive chargers do better???. I would say 14.8v is the minimum charging voltage for an off grid boat. ............Dave

You'll need to get that hole in the bottom welded up otherwise you might sink. ..............Dave

Liverpool is not very dog friendly and most pubs won't let them in. Luckily the Baltic Fleet does and that's probably all that matters. The Albert dock area is "no dogs" but nobody complained, not even the security men. There is an area just up the steps from the pontoons, next to the main road (separated by a wall) that is adequate for doggy needs. Not the best but lots of boat dogs use it so it has interesting smells (for dogs). You will obviously need to pick up and at weekends the rubbish bins can get very full. You can use the slope if the dog does not like steps, its only a little further to walk. Amazingly you can take the dog on the (underground) train over to the big beaches on other side of the Mersey, but it sounds like your dog might be a bit old for seagull chasing. Liverpool is good. .............Dave

When I left work (and bricks and Mortar) to move onto the boat a few years ago I had to get rid of (re-home) quite a few reel to reel tape recorders (including some good and unusual ones). I was pleasantly surprised about how popular old tape recorders are, and how fanatical some collectors are. Made some serious money! Unless you have cash to invest maybe stick with the radios! ............Dave

Kept a spare portapotti under the bed for 6 years without using it so decided the space could be better used for storing other useless possessions. Secret is to keep an eye on the weather forecast and never let the pump out get more than 2/3 full. However Left it a bit late at Hungerford, as we were only 500yds from pump out. But.... Pump out not working and CaRT man who handles these things on holiday!!!! Went to Bedwyn, pump out at Bedwyn also not working. Firm phone call to CaRT, man on holiday no longer acceptable as excuse. Good response from local CaRToffice and pumpout fixed next day! Would have been rather nice to have excuse go to pub every night ... but always need a c**p in the mornings! ...........Dave

You could try using a "powered hub" to get over the power issue, some are very cheap, but there may be other problems too as I am not clear about what sort of file system the iPad uses. Its on my list of things to learn about but boating takes priority! We use the camera lead thing to connect a USB sound card to connect the iPad to the boat stereo (car radio) ............Dave

Yes, but what about the voltage across each cell ????????