Installing Inverter

[Ray_G]

I already have shorepower and an onboard generator with manual switching between the two to provide 220v AC power. I have just purchased a 1000 watt inverter and wish to wire this into the system so that (through the inverter) I have power at each AC outlet. Can anyone help with a wiring diagram to do this, and what sort of switching arrangement will be necessary?

 

[HaraldS]

I could send you my AC wiring diagramme as it has about what you are looking for. You should find out if your selector switch directly switches between generator and shore power, or if it does it indirectly turning on the appropriate realis that bridges the selected power source to your internal AC net. In the later case you would need a third relais and a three-position selector switch.

Most use relais, as three-way two pole switches that can take the full load are hard to get. But be warned of a potential problem with the relais approach: Relais tend to fall off slower than they kick in. That means if you turn the switch, the old source might not be disconnect before the new one connects. In the case of shore power and generator this doesn't matter much, but for most inverters that's deadly.

The only exception I know of, are the Victron inverters, which you can actually leave connected, as they sense the power and can even "assist" a generator if temporarely a higher load than what the generator can support is needed. Also in the Victron case you wouldn't need to extend your seletor switch, as you could wire it directly to the internal AC net, and it would just kick in if the other power sources are inadequate.

For normal inverters it is safer to use a 5-pos switch with zero positions in between, or an electronic delay circuit for the relais. Also possible to wire the three-way switch with Shore-Gen-Inv, then the most likely mistake of swicthing from Inv to Shore, isn't possible and you could make it a habbit if switching to Generator, before starting it.

 

[Ray_G]

Thanks for that: your response is most helpful. If you can send me your wiring diagram I would be grateful. Do you have a Fax? If so send it to 01767 641755 please.
Thanks again.

 

[nicho]

My new boat will have 2x140amp/hour batteries to power the on board 12 volt systems (engine start battery is separate) - I understand the principle of inverters in that they enable a 240 volt implements to operate from the 12volt system, but can anyone advise how long it would be before say a 14" colour television or 800watt microwave flattens the batteries?. Are inverters only for short term use, or do the batteries manitain enough power to keep such items going for some time? - obviously, if we are plugged into shorepower it isn't necessary.

 

[davel]

Basic equations to use are:
Watts = Volts x Amps therefore Amps = Watts/Volts

Batteries should be expected to deliver about 40% of their capacity

Given your examples then,
800 watt microwave will require approx 800/12 Amps = 67 amps
Your battery bank will deliver approx 2 x 140 x .6 Ampere hours = 168
So Microwave will operate for 168/67 hours = 2.5 hours approx (more than enough to warm up your pot noodle). This assumes that no other items are utilising power which isn't the case of course.
Perhaps a better way of expressing this would be to say that 1.5 minutes worth of microwave use will consume approx 1% of your fully charged battery capacity (ie 1.5 x 100 =150 minutes which is 2.5 hours).

Most small TVs consume about 75-100 watts.

Dave L.

 

[HaraldS]

FAX went out. Hope it's readable. If not we can try e-mail. I have it in AutoCad, but could probably paste it into Word. Just let me know. Also if you have any questions about it.

 

[Ray_G]

Fax received but non too clear. Could I trouble you to paste it into Word and e-mail it to me at ray.gorringe@kier.co.uk
Thanks

 

[nicho]

Davel - a perfect reply - tells me all I want to know, many thanks

 

[Robin2]

I have heard that microwave ovens are not at all happy with the quality of electricity produced by many invertors. I have no experience - my microwave is only connected to the mains.

 

[tyger]

Just a few things to add to Dave L's post.

1) The capacity of the battery decreases as the current drawn increases.
e.g. a battery may be rated at 125 amp hours for a 5 amp draw. If you draw 100 amps the apparent capacity of the battery may decrease to (say) 90 amp hours.
(I forget the name for this effect).

2) As Dave pointed out it is recommended that you use only 40% of a battery's nominal capacity to avoid over discharge reducing its useful life.

Combining 1 and 2 gives a useful capacity of 125x0.9x0.4=45 amp hours

In other words you could safely run a device drawing 100 amps for 45/100 hours or about 27 minutes and not 75 minutes as a simple calculation might suggest.

3) To calculate the current drawn it is safer to use 11 volts rather than 12 since inverters are only about 90% efficeient.

Thus your microwave would draw 800/11 = 73 amps.

However unless you are pushing things to limit this should not be a problem.

4)Large inverters are tough on batteries. To run your microwave you would probably need a 1KVA inverter. To support this you need deep cycle batteries.

5) Make sure that the dc cables from the batteries to the inverter are properly sized. Fit a high amperage fuse between the battery and the inverter (the installation instructions should give the correct rating.

Hope this helps.

Terence

 

[tyger]

Re: Running Microwaves on Inverters

To answer Robin's point, there are two types of inverter:
1) Those that produce a true sine wave. These are expensive but will support any device that will run on the mains (subject to capacity).
2) Those that produce a modified sine wave (a "stepped" square wave). These are less expensive. They will support most devices but can give problems with devices that are controlled electronically.

Devices that may not work properly with modified sine wave inverters include: microwaves, VCRs, stereos, electronic light dimmers, variable speed power tools, laser printers etc.

The only device with which I have experienced a probem using aq modified sine wave was a Sony TV with a built in VCR. We a Heart Freedom 25 inverter/charger on our liveaboard. The TV worked well for broadcast programmes however the VCR was unusable due to tracking problems. To watch a video we had to run a generator.

We did not have a microwave aboard. I understand that in general they will operate on a modified sine wave but at reduced power - so cooking times need to be extended by trial and error.

Terence