Bob18

Different animals. The Varta is a targeted at the automotive engine start market, and from the description of its duty cycle I'd guess the local delivery van in particular (lots of start/stop cycles) which is a bit different to that of a narrowboat, where it tends to be start, run for a few hours, stop. The Odyssey is very much more a deep discharge battery, with good engine start capabilities. Odyssey are good batteries, but very expensive, and are quite light for their rating - 60kg for 200Ahr beast is at the low end of weight for 200Ahr batteries - one battery manufacturer I've worked with over the years quotes a 150Ahr, similar duty battery as weighing about 55kg. In general more weight = more lead = longer life in a given duty. As for practicality, the "edge-on" connectors are not very easy when you are paralleling up batteries, much easier with the more traditional top connector, of course being a sealed AGM you can tip the battery on its side

I go for blind rivnuts for smaller stuff. The only down side is the mandrills tend to hide in the most remote corner of the tool box as soon as they know you are looking for them....

And it comes in a variety of flavours. Anyone fancy a curry tonight?

I'm not sure who does them, but magnetic catches are used in hospitals to hold their massive fire doors open while trolleys are wheeled through.

I quite agree with almost everything Ditchdbaler says, the only (minor) error is that its not any residual alkali that wrecks the seals its any residual methanol, and the esterified veg oil itself. Residual alkali will go for any aluminium bits in the system first, then the copper/brass, then the steel... And of course, with changes in the law, we are now getting a few percent of "properly brewed" bio-diesel when we buy new diesel - the initial proposed level was far higher, but all the engine manufacturers shouted at once to say "No, if you do that, we'll be sending you the bills for all the engines you wreck"

Got to be worth a go, even at the inflated £4.99 a litre. (adds "paint bilges a light colour" to list of things for my boat spec...)

Interesting, I looked at a couple of sites flogging these inverters, and the OEM site, and got three different overload ratings, 3600, 4500 and 5400. Being a pessimist when it comes to how people state their ratings I'd go with the lowest, and that is "marginal" for the fridge - sometime it will, sometimes it won't, but never will when you want it to be nice and peaceful. If everything else is OK, then its one of the options listed in the original post - I'd start with a decent soft-start device, if it works its only a few tens of quid compared to the hundred/thousands for the others. (Ignore comments about cutting out the alarm, there may be a time when its a "real" alarm and not a transient one...)

There is a tax free allowance for home brew bio-diesel, provided it is only for you own use. I think its something like 2500 litres per year, but only if you "brew it and use it" yourself. A big problem, that others have identified, is getting hold of a reliable source as most "chippies" are tied into one of the major oil recyclers, which is to their advantage, these guys sort out all the paperwork for the chippy, who just carries on frying as usual...

The way I read the original post is that its when the fridge kicks in, so I think we can rule out any inrush capacitors on the inverter whining. A couple of questions - Does the same thing happen when a heavy resistive load, like a kettle get plugged in? And, what make and model is the inverter?

In my experience as a former user of Numax batteries they are over priced for their quality.

There are two ways of using old cooking oil. First (cheapest) - Filter out all the muck and water and tip in the tank. You need to use the right sort of filters and keep them clean. You obviously have to get rid of the rather gooey, smelly waste, please don't dump it either the drains or the cut. Second (expensive) - This is the chemical process. Its called esterification, and is not for the faint hearted. First filter it as above, then add caustic soda and methanol, then clean it up again. You end up with a lot of very unpleasant chemical waste to get rid of which really must NEVER go near either the drains or the cut. I'd go for the first, but to run it all year you either have to "cut" it with normal diesel in the winter, and how much ordinary diesel you needs depends on how cold it is. The real downside is the smell, but this can be managed by choosing your source to suit your taste buds

Two possible "charging efficiency". First - how many of my charge cycles will it take before this battery is dead (unable to accept a sensible level of charge). Second - how much energy is used by each of my charge cycles, compared to the energy supplied by the charging system. (On a boat this sort of equates to how many hours do I have to run the engine to get the battery recharged) Simple answer to both - It depends on your battery, your discharge cycle, your charge cycle, and how well you look after your battery between cycles. If you discharge a battery at an excessive rate to a moderate/deep discharge it will not last as long as the same battery discharged at a more gentle rate to the same depth of discharge. If you repeated "crash charge" a battery from a given discharge you will reduce its life. If you charge a battery too slowly for its state of charge you will reduce its life. If you let the battery get too hot, or too cold, you will shorten its life. Very rapid charging is less efficient than a more gentle charge. Too low a rate of charge is less efficient than a sensible rate. If you don't periodically inspect a battery, and top it up as necessary you will reduce its life. People often forget that how you discharge a battery is just as important as how you charge a battery, and each battery has an optimal discharge rate - Take a look at the discharge rate tables for the battery you are considering. These tables should give data for discharge rate, discharge depth, charge voltage, charge current, and probably not just at one temperature, but a range. Most discharge curves are quoted at "C5", "C10", "C20" and so on, quite simply this is the capacity in Amp hours divided by the number, so a 100Ahr battery being discharged at the C5 rate is delivering 20A, and the same battery at the C20 rate is delivering 5A.

Ahh, the joys of battery life. Most batteries are sold on a so many YEARS of life, but in reality they are designed with so many CYCLES of life in mind. Thus you might have a battery that is sold as having a four year life (read that as a four year warranty) in reality it is designed with a 400 cycle life, where a cycle is defined in terms of say a 50% discharge, followed by a correct recharge. The manufacturer will have taken a guess at how frequently the battery will be discharged to 50%, then recharged to something near its optimum, lets say he guesses at every three to four days (averaged over a year), he now rounds that a bit and gets a four year life expectancy. I Hear you cry "But I never discharge my battery to that extent". Fair comment, but do you discharge it very gently, or do you hit it with a dead short? The manufacturer will have designed the battery with a particular discharge rate in mind, move away from this and you are onto a new pitch, you may be lucky and have a battery that performs far better on a gentle, shallower discharge than his design intent, but equally you may be unlucky and have one that is woefully short lived under those conditions. The "good" battery manufacturers have tables of data showing how discharge rates, discharge depths, discharge frequency, charge regimes, storage temperature, operating temperature, inside leg measurements, etc, all affect the life expectancy of one of their batteries. Then we move onto the question of battery charging. A real thorny one this. To charge a battery you need to apply a voltage that is above the current cell voltage, quite obvious really. So you have a cell that is at 1.9 volts, now do you apply 1.91V, or do you apply 2.2 volts? It depends on a number of things, not least of which is the designed charge voltage for that cell at that level of discharge. For most cells you need at least 0.25 volts of over voltage to even start charging at a sensible rate, so the minimum charging voltage for a 12v (6 cell) battery is 13.5V, most cells work best at about 0.5V over voltage, so you need a charge voltage of about 15V. You have to apply this voltage until the battery has reached a sort of equilibrium state, normally when its about 80-90% charged, you now reduce the over voltage somewhat, and continue to charge until the next equilibrium point is reached, you reduce the voltage again and "float charge", again at reduced over voltage - well that's the ideal. Every decent battery manufacturer will tell you exactly what voltages to use, what temperatures to control the battery to and so on. Now for reality - The average cheap charger just stuffs a few volts on, and the current goes through the roof for a few minutes, dropping away as the charge glows in the corner, the battery is sort of charged, maybe to 80%, maybe to 90%, who knows? The charger certainly doesn't, the battery life will be adversely affected, there is the danger of a lot of gas being produced because the battery has been overheated (Do I need to spell out the dangers of a gassing battery??). Sadly most alternators come into the same category as cheap battery chargers, bt they do shove out more current so do things wrong more quickly... So what? you ask Well buying a cheap battery that is going to last a year or so may be OK, but it will only last a year or so (anything more is a bonus). Buying a cheap battery charger won't help the life of any battery if used regularly. I'm in the process of specing-out a boat. The batteries will not be the cheap throw away ones, but a decent set of not so cheap ones, supplied by a major battery manufacturer who will sit down with me and go through my load calculations, my charging requirements, and the expected battery life (currently I'm looking at a seven year warranty, full replacement to five years, then tail off) and they aren't anything like seven times the price of a throw-away set, not are they a "fancy" technology like Li-ion, they will run off a "standard" Mastervolt or Victron charger (or C-Tec), I will only have two battery types on board - a bank of big ones (150Ahr each) for domestic, main engine start, bow thruster and a single little one (55Ahr) for the generator start (but that will be man enough to start the main engine. My only concern just now is getting an answer about managing the output from the alternators, but that will come in time for the purchase.

A few things. First, and by no means least, fridges (and air-con units) are notorious for their massive start up currents. You can expect to see a small compressor attempting to draw 10 to 20 times the run current. So if your fridge runs with 1A, you could be seeing a start-up current of about 20A, and 20A at 230V is 4600W "instantaneous" demand, possibly for as long as a second in the worst case. I doubt that your 1800W (continuous rating)inverter is capable of doing that without some sort of protest. If the voltage at the input to the inverter is low then it will run into overload much sooner than if the voltage is at, or above, the nominal. So for you 24V system if the input voltage is below 24V then you are going to hit a limit sooner than if its above. 25.7 is a pretty good voltage, but what happens when you put a smallish load on (say the tunnel light)? If there is more than 0.1V drop you could be heading into battery problems... During start the input voltage to the inverter will drop, how far depends on the battery capacity, the state of the batteries, the type of batteries, the wiring, the state of the wiring. If you have a multi-metre which has max/min capture capability it will be possible to see what the inverter input voltage is doing during that first couple of seconds of a fridge cycle, you may be in for a shock! The situation will be worse if you have a low cost "quasi-square" (sorry, "quasi-sine"), or "modified sine" inverter. Several reasons for this, but generally they just aren't as well engineered as the more expensive "pure sine" inverters. Compressors are hard to start for a number of reasons, including: Trapped refrigerant, if the fridge is "short cycling" then the refrigerant will not have time to get back to the right place before the next start. For most domestic fridges the time between stops and starts should be a few minutes. Small ones tend not to have by-pass valves, which are opened to allow the compressor to speed up under virtually no load, then progressively close. Obvious really, if you start under no load then its easier to spin... Then there are things like start windings, which are designed to give high torque, start capacitors, split windings (you only use "half" the motor for a few seconds) Variable frequency drives (getting a bit fancy, you ramp up the frequency from almost DC to 50Hz, which reduces the peak current demanded (and a few more...). Such things are rarely fitted to small domestic fridges because of COST. From what I've seen of these they tend not to have even a start winding or start capacitor , but are "full load" synchronous motors. So, what can you do? First, check the STATE of the batteries, not just the voltage, but their ability to deliver a decent amount of current at the terminals (borrow one of those old fashioned high current discharge tester that garages used to use). Second, check the STATE of the inter battery wiring, 35mmsq minimum between the cells, to the isolation switch and to the distribution panel. Third check the STATE of the battery isolation switch, fuse holder, and wiring to the inverter - which should be AT LEAST 25mmsq (If the battery is really very close close to the inverter, you may get away with 16mm sq, but only if its really close say 1m on each of the pos. and neg cables from the battery). Make sure all connections are secure, and no visible damage to visible cables. Forth, check the STATE of the mains wiring (with it turned off and isolated....). Make sure all connections are secure, and no visible damage to visible cables. Good luck, and if all else fails, ear plugs.... Bob

While YOU may have no plans to sell in the next five years a "higher authority" may have plans that force a sale in that time period, so the RCD route is a "safe" one to follow. And don't forget that RSS cuts in sooner, and some marinas all but insist on an RSS, even on a new boat.