Use of inverters on boats?

[C08]

I was wondering about using a small microwave on the boat but the concept of 60/70amps for a few minutes is a concern for my batteries, apart from the start up surge that I understand can be double that sort of already high current. This seems a recipe for destroying batteries or am I worrying uneccessarily?

 

[PaulRainbow]

Depends on the microwave, inverter and batteries, you didn't give any info on either.

 

[Kelpie]

It's in the same ballpark as a windlass, so not that daft an idea. But you will want to keep the wiring runs short.

 

[William_H]

While quite expensive compared to domestic M/W you can get a 12v or 24v microwave which will use somewhat less current and hopefully without large on surge current, and not need an inverter but yes will still punish even a large battery bank. OP has not said how big his batteries are. ol'will

 

[Richard10002]

I was wondering about using a small microwave on the boat but the concept of 60/70amps for a few minutes is a concern for my batteries, apart from the start up surge that I understand can be double that sort of already high current. This seems a recipe for destroying batteries or am I worrying uneccessarily?

I had a microwave on my Moody 44 between 2006 and 2010. It came with the boat, and it was a Sterling inverter, (probably from 2004).

I use a Nespresso Coffee Maker on the narrowboat, and it draws 90A for a few minutes at a time. No problem from a Sterling 2500W Pro Combi S.

I'd say that, as long as you set things up properly, you will be worrying unnecessarily

In terms of "punishing" a battery bank, 70A for 5 minutes is only 6Ah. Your starter draws hundreds of Amps for a few seconds when you start your engine, but very few Amp Hours.

 

[Neeves]

For the current they draw and the scarcity of current on a ' common' or 'normal' yacht we do not think they are worth it. Almost anything if not everything that a microwave can do you can also do with a conventional gas hob (and, to us, if you want to bake use a gas oven, or BBQ). We have a 400amp/hr house battery bank and an inverter and have not used the microwave for years (not true - we keep the keys in it).

Save your money buy a steamer to fit your saucepans, relax and wait for the food to cook slowly - like Grandma used to do it .

We do need the inverter - the iPads, computer, camera etc need to be recharged and they are deemed so much more important, essential, than a microwave.

Jonathan

 

[pcatterall]

For the current they draw and the scarcity of current on a ' common' or 'normal' yacht we do not think they are worth it. Almost anything if not everything that a microwave can do you can also do with a conventional gas hob (and, to us, if you want to bake use a gas oven, or BBQ). We have a 400amp/hr house battery bank and an inverter and have not used the microwave for years (not true - we keep the keys in it).

Save your money buy a steamer to fit your saucepans, relax and wait for the food to cook slowly - like Grandma used to do it .

We do need the inverter - the iPads, computer, camera etc need to be recharged and they are deemed so much more important, essential, than a microwave.

Jonathan

Our microwave is indispensable ( for us). We are in Spain and the microwave limits the amount of heat down below. Most use is when on mains but our inverter does the job when out and about!
Why use an inverter to provide dc power for your electronics? isn't it more effective to use your batteries with an adapter?

 

[Boater Sam]

An inverter supplying a microwave has to be a proper pure sine wave jobbie else the micro will get annoyed and noisy, won't work.

 

[jwfrary]

If you stick at or near a 2c discharge rate then the impact on the batteries will be low

However like any consumables batteries do not last forever

 

[PaulRainbow]

I was wondering about using a small microwave on the boat but the concept of 60/70amps for a few minutes is a concern for my batteries, apart from the start up surge that I understand can be double that sort of already high current. This seems a recipe for destroying batteries or am I worrying uneccessarily?

Firstly, you will not get a microwave that only draws 60/70 amps. For instance, the Daewoo QT is a 600w oven, that's 600w of cooking power, not 600w of supply current. It's max supply current is actually 1000w and that will equate to a 100a draw from your batteries, 5ah for every 3 minutes it's on. When you have access to shore power, using the microwave is a no-brainer, IMO, it's much cheaper than using expensive bottled gas and obviously faster too. As long as you have the ability to replace what it uses from your battery bank running it from an inverter is little different to anything else that consumes battery power. If you use it to deplete your batteries to a dangerous SOC, then it will kill them, same as anything else will.

You'll need at least a 1200w inverter and it should be pure sine wave (although some microwaves will run on quasi sine wave, i wouldn't recommend it).

 

[PaulRainbow]

For the current they draw and the scarcity of current on a ' common' or 'normal' yacht we do not think they are worth it. Almost anything if not everything that a microwave can do you can also do with a conventional gas hob (and, to us, if you want to bake use a gas oven, or BBQ). We have a 400amp/hr house battery bank and an inverter and have not used the microwave for years (not true - we keep the keys in it).

Save your money buy a steamer to fit your saucepans, relax and wait for the food to cook slowly - like Grandma used to do it .

We do need the inverter - the iPads, computer, camera etc need to be recharged and they are deemed so much more important, essential, than a microwave.

Jonathan

But using an inverter for charging DC devices is just throwing energy away. Why not use some DC-DC converters ? I have dedicated DC-DC converters for phones, laptops, TV, soundbar and several USB sockets, all running from the batteries which are charged by solar power.

Of course you can heat a can of soup up or reheat something, but that uses several minutes of expensive gas, whereas a microwave would only take a couple of mins and use about 3ah from your batteries, how long would that take to replace with your solar panels ?

 

[pvb]

It's also worth remembering that battery capacity reduces with higher discharge currents (as discovered by Herr Peukert). So, for example, a 300Ah domestic bank discharged by 100A would realistically only have a practical capacity of about 120Ah, and would be 50% discharged in a little over half an hour.

 

[RupertW]

But using an inverter for charging DC devices is just throwing energy away. Why not use some DC-DC converters ? I have dedicated DC-DC converters for phones, laptops, TV, soundbar and several USB sockets, all running from the batteries which are charged by solar power.

Of course you can heat a can of soup up or reheat something, but that uses several minutes of expensive gas, whereas a microwave would only take a couple of mins and use about 3ah from your batteries, how long would that take to replace with your solar panels ?

So you are saying that DC to AC to DC (battery to invertor to DC adapter) is wasteful but DC to AC to DC (a DC-DC converter) is good? It’s the same electrical transformations in the same order. The differences will be in the efficiency of each component and either solution could be more efficient.

 

[CLB]

Firstly, you will not get a microwave that only draws 60/70 amps. For instance, the Daewoo QT is a 600w oven, that's 600w of cooking power, not 600w of supply current. It's max supply current is actually 1000w and that will equate to a 100a draw from your batteries,

You'll need at least a 1200w inverter and it should be pure sine wave (although some microwaves will run on quasi sine wave, i wouldn't recommend it).

I was going to say the same thing. It's worth pointing out that many domestic microwaves are now 700W minimum and draw 1200-1400w on full power. They could easily be drawing 120A and will really need a 1500W pure sine wave inverter

 

[pvb]

I was going to say the same thing. It's worth pointing out that many domestic microwaves are now 700W minimum and draw 1200-1400w on full power. They could easily be drawing 120A and will really need a 1500W pure sine wave inverter

I bought a cheap 2000W pure sine wave inverter for my boat. It will run the microwave easily and is also used for a 1200W hairdryer. I reckon cheap inverters are borderline at anything approaching their rated output, so it's best to buy a bigger one than theoretically needed. If buying a Victron, that idea doesn't apply.

 

[CLB]

I bought a cheap 2000W pure sine wave inverter for my boat. It will run the microwave easily and is also used for a 1200W hairdryer. I reckon cheap inverters are borderline at anything approaching their rated output, so it's best to buy a bigger one than theoretically needed. If buying a Victron, that idea doesn't apply.

I am sure that does apply to some cheap inverters, so worth noting. I have a cheap 1000w inverter and it will happily run a 1kw continuous load, although it does have, supposedly, a 2kw surge capacity.

 

[PaulRainbow]

So you are saying that DC to AC to DC (battery to invertor to DC adapter) is wasteful but DC to AC to DC (a DC-DC converter) is good? It’s the same electrical transformations in the same order. The differences will be in the efficiency of each component and either solution could be more efficient.

Pretty sure that's not what i said.

 

[Graham376]

So you are saying that DC to AC to DC (battery to invertor to DC adapter) is wasteful but DC to AC to DC (a DC-DC converter) is good? It’s the same electrical transformations in the same order. The differences will be in the efficiency of each component and either solution could be more efficient.

I can charge computers from either inverter using normal mains adaptors or, from 12v using power bricks to 19v. The latter use about 50% less power than charging through inverter.

 

[RupertW]

Pretty sure that's not what i said.

Um, you said “But using an inverter for charging DC devices is just throwing energy away. Why not use some DC-DC converters ?”
That sounds to me like saying “DC to AC to DC is good. DC to AC to DC is bad” - how else am I supposed to read your sentence?

Genuinely though, surely if you are doing the same transformations electrically in your first sentence and your second sentence then it’s all about the efficiency of each particularly component.

 

[PaulRainbow]

Um, you said “But using an inverter for charging DC devices is just throwing energy away. Why not use some DC-DC converters ?”
That sounds to me like saying “DC to AC to DC is good. DC to AC to DC is bad” - how else am I supposed to read your sentence?

Genuinely though, surely if you are doing the same transformations electrically in your first sentence and your second sentence then it’s all about the efficiency of each particularly component.

Modern DC-DC converters are vastly more efficient than they used to be, generally not using rectifiers any more, up to 98% efficiency.

Sterling quote up to 85% efficiency with their small inverters and a 0.95a current draw at standby.
Victron do better at 87% - 92% (smaller = less efficient). Standby current for a modest model is about 0.7a

I just looked at the 2 DC-DC converters that power my TV and Soundbar (one for each) and the current with no load is unmeasurable with my monitors. If i turn the soundbar on i see a .95 current draw, coincidently the same as the Sterling inverter uses when it's doing nothing.