--- In [email protected], Trevor <listsandst...@...> wrote: > > Can I ask a couple of quick questions whilst we are on this subject ... > > 1] Is it feasible/safe or totally inadvisable to run the engine > alternator (whilst the boat is underway, for example) and run a portable > generator at the same time? > > 2] I normally switch my inverter 'off' when running the genny as it has > an 'either/or' switch incorporated, i.e. if I'm getting 230/50 from > another source the switch automatically isolates the potential output > from the inverter. I'm not sure how much current the inverter uses when > left 'on' but figure that I would prefer as much charge as possible to > go into the battery banks. The problem is that I have been known to > forget to switch the inverter back on again after closing the genny down > - so is it worth bothering to switch it off in the first place? > > Trevor >
As you specify "portable generator" I assume that you are talking about something like the Honda EU range. What I say probably applies to most other generators as well. First of all if you are using the 12V output to attempt to charge batteries the current is so low you may as well forget about it. If you using a generator of any type or even a shoreline to drive a battery charger then although you are unlikely to do any damage the question of its effectiveness is hard to answer without lots of whys and wherefores. I assume you have just started up in the morning after a night of "typical" current usage. Any decent charging device will be measuring the voltage so it knows when it has to take action to prevent battery damage caused by excessive voltage. Typically this will take place (for wet, open cell batteries) at something between 14.00 and 14.5 volts at which time the charger will regulate its output to that figure. This is usually known as the bulk phase of charging. Now, at first the charging volatge will be well below that figure so none of the charging devices will want to regulate their volatge so they will all be putting as much into the batteries as they can. However the moment one of them reaches the charging volatge set by their own regulator they will start to try to regulate the volatge. If one of the devices has a higher regulated volatge setting the device with the lower setting might in effect shut down because its assumes the batteries are fully charged. Thats fine if its a 10 amp charge that shuts down but leaves a 70 amp alternator running, but what if its the other way round? At that stage with the voltage regulator(s) working we are said to be in the acceptance phase of charging and this will go on for a long time until any device equipped to decide the batteries are now fully charged will reduce the charging volatge to about 13.7 and hold it there. This is known as the float charge phase. Good charges should do this but alternators will not. So in answer to question 1. There may be an advantage during the bulk charge phase but once the regulators start working you could well make things worse by leaving both running. Again answer 2 is far from straight forward unless we know exactly what your inverter is. If its a combi-unit which is inverter and charger combined then turning it off may prevent its charger working and if you are using the generator's 12v output to do the charging you will be wasting a lot of potential charge. If it is just an inverter and you are charging via the 12 volt output then for goodness sake turn the inverter off, you probably have less than about 5 to 7 amps charging current anyway. If you are using the generator to drive a charger of reasonable output then I suspect it will not make overmuch difference. The 5 amps I quoted is probably at the top of the inverters' working current range and a good quality modified sine wave one may draw far less. Some inverters switch into a standby mode when no load is applied. If yours is one of these I doubt you will gain much by switching it off when charging. Tony Brooks
