| Power inverters | | | | performance and possibly tripping the inverter. You |
| Computers, hi-fi and microwave ovens use | | | | need proper cable from a battery dealer or |
| considerable power, so if you're considering using | | | | automotive electrical supplier. Measure the exact |
| them on board you'll probably need power inverters. | | | | length you want before you buy. They will probably |
| An inverter is probably one of the first extras most | | | | crimp the terminals on for you, but check the |
| owners consider buying for their boat, whatever size | | | | diameter of the studs. Most batteries will be 8mm, |
| it is. The ability to use 240V equipment when you are | | | | but the inverter may be l0mm. |
| on passage or moored away from a shore supply is | | | | If you have to mount the inverter further away, use |
| prized by most people. At the same time, an inverter | | | | 70mm cable, or two 35mm cables in parallel for both |
| is one of the easiest items to install, providing you | | | | positive and negative. |
| understand the basic steps involved. Inverters range | | | | Unless a main input fuse is already fitted, you'll have |
| in size from 50W to 4kW, and can power most | | | | to fit a 250A fuse in the supply line. It's also a good |
| items that you now plug into the mains, but you | | | | idea to have a separate battery master switch in line, |
| need to understand their limitations, and for that you | | | | so you can disconnect the unit completely. This must |
| need to understand what makes them tick. | | | | be capable of taking 250A continuous load. Check the |
| How they work An inverter takes low-voltage direct | | | | size of its terminal studs - they will usually be l0mm. |
| current (DC) from batteries, usually 12V or 24V, and | | | | The DC input terminals on some units were very |
| converts it to high-voltage alternating current (AC), | | | | close together, risking short circuit. If there are no |
| either 110V, 230V or 240V. The process is the same | | | | plastic terminal covers, fit your own. |
| as your battery charger, except in reverse, and | | | | Your battery bank is a major consideration when |
| some combi models double as chargers, using the | | | | fitting any but the smallest inverter ...If you take |
| same basic electronics inside. Early inverters used | | | | 200A out of a fully-charged 200Ah bank, the voltage |
| transformers to step the volts up, and were heavy, | | | | at the battery terminals will drop from 12.6V to 11.0V |
| but most modern models use solid-state electronics, | | | | at the inverter. If the bank is only half-charged, the |
| both to step up the voltage and to convert the | | | | voltage could be down to 10.5V, close to the low |
| current from DC to AC, and are correspondingly | | | | voltage tripping point of 10.0-10.5V. |
| lighter. | | | | If you're fitting a 21kW inverter, you should have a |
| Domestic mains supply voltage follows a sine-wave | | | | minimum of 400Ah batteries, preferably 600Ah. For a |
| form with a rounded top as the current alternates. | | | | 1 kw unit, you will need 200Ah, preferably 300Ah. |
| But, while this wave form is easily produced by a | | | | All these figures assume the engine is not running, |
| rotating generator in a power station, it's more | | | | which is the usual situation when moored. If you start |
| complex and costly to produce electronically and | | | | it up, you will get an input from the alternator, and |
| wastes more power. Instead many inverters use a | | | | the battery volts will rise, which will improve the |
| modified sine-wave, or quasi sine-wave, which has a | | | | situation, but you should not rely on this. |
| flat topped or square curve. The modified sine-wave | | | | The condition of your batteries is also important. High |
| powers most AC equipment, but can struggle with | | | | continuous current drains will hammer the bank, and |
| some items, particularly electronics with internal | | | | quickly find out any weak cells. Gel or AGM batteries |
| power supplies and digital timers like computers, TVs | | | | will be better able to handle continuous heavy loads. |
| and microwave ovens. Recently the internal power | | | | The 230V output from the inverter will be either one |
| supplies for most electronic equipment have changed | | | | or more sockets on the front, or you may have to |
| to switch-mode systems, which better handle poorer | | | | hard-wire a cable internally Again, only do this if you |
| quality incoming AC. At the same time, the standard | | | | are sure of your proficiency. UK three-pin outlets are |
| of the best modified sine-waves has improved | | | | best fitted sideways or upside down so that large |
| markedly, close to that of a pure sine-wave. | | | | plugs or power-supplies dont foul the base. |
| Yacht batteries and marine batteries | | | | Because the inverters have to be close to the |
| An inverter can provide high outputs but all this | | | | batteries, they will usually be mounted in the engine |
| power has to come from your batteries. Short burst | | | | space, or at least away from the galley area. But |
| high power appliances like a microwave oven, kettle, | | | | because most of them have a continuous residual |
| toaster or hair-dryer are fine, but to run heaters or | | | | current drain in standby-mode, you don't want to |
| machines for long, you need a very large battery | | | | leave them permanently switched on. A remote |
| bank or engine power. | | | | control panel allows you to turn off the inverter |
| As we have said, virtually anything that you now plug | | | | when it's not needed. |
| into the mains can be run from an inverter, but the | | | | Ideally you should fit a change-over switch in the |
| size of your unit governs what it will power. Up to | | | | output circuit to switch the incoming AC power |
| 500W you can run computers, TV, hi-fi, battery | | | | between shore supply, generator, and inverter. It's |
| chargers for your mobile phone and cameras, and | | | | important that you don't have two different power |
| even a 240V domestic fridge, though not always all | | | | sources feeding into your ring main at the same time. |
| at the same time. | | | | Make sure you get the polarity right when connecting |
| Up to 1,000W, and you can add a small travel | | | | the DC or you could damage the unit |
| hair-dryer. For most people however the big plus is | | | | Any piece of electronic equipment will give a high |
| being able to run a microwave oven and for this you | | | | short-term output, but will quickly cut out as it heats |
| will need at least 1,500W, preferably 1,800W. Don't | | | | up. Best practice is to use the continuous rating to |
| be confused by the 60OW or 80OW rating on most | | | | describe the unit. Having said that, the intermittent |
| microwaves. This is the useful cooking power they | | | | rating is important, as some pieces of AC equipment, |
| generate, not the amount of power going in, which | | | | particularly those with motors in them, have a |
| will be double this figure. | | | | start-up surge that needs a short burst of higher |
| And at this size, your inverter should also power a | | | | power. |
| standard hair-dryer, plus possibly a kettle, toaster and | | | | Most power inverters drain a continuous current |
| coffee-maker, though these may require 2kW. | | | | when switched on, even when you're not using them. |
| Installing an inverter is within the capabilities of a | | | | This standby current will be at least 2A, sometimes |
| competent DIY electrician, but if you've any doubts, | | | | more, which, over 24 hours, it could drain 50Ah or |
| leave it to a professional. A 2kW, 12V inverter will be | | | | more from the batteries. |
| drawing up to 200A from your batteries, more than | | | | This is why a remote control is important. Some |
| many engine starter motors, so you need large | | | | models have a powersave mode. This sends the unit |
| diameter cables, short runs, and good connections. | | | | to sleep while nothing is connected and wakes it up |
| For the higher output models, use 50mm cables | | | | when it's needed. The drawback to this is that tiny |
| (35mm for lower outputs), a maximum of 1.5m long | | | | currents, like the timer light on a microwave, will not |
| with properly crimped lugs, not screw connectors as | | | | trigger the unit, so the microwave won't start. Your |
| they work loose. Anything less and you could lose | | | | mobile phone charger will also probably not activate |
| too much power down the line, which means reduced | | | | the inverter, so you still need to turn it on manually. |