Leisure Battery

Perhaps he's looking for 'a Motorhomes guide'...?

We’ll probably never know. I’ve lost count of the number of one-off requests for technical help on here that just fade away without any follow-up from the op. Clarification is sought, signposting given and information provided, but only very occasionally is anything further heard. Perhaps this one will be different? 🤞

Your battery size will dictate how long it can support the microwave use....not whether it will run, this will be down to the inverter.....it's size, output and, perhaps, if it's pure sine wave or not.

remember, a microwave start up current draw might be three times the size of the rated value.

https://gpelectric.com/which-inverter-do-i-need-to-run-a-microwave/

From my experience over the years using microwaves via an inverter on several hired narrowboats, the boatyards advice was usually to run the engine whilst using the microwave for the brief period involved.  Narrowboats usually have 2 or 3 huge leisure batteries and a huge inverter. Out of curiosity I did try with and without the engine running and the difference was very noticeable. 

While I have to agree that Lithium seems to be the way forward they are very expensive to purchase and from some accounts I've read they are not always compatible with the standard battery chargers.

Very true and from what I have read the alternator and solar panel systems must also be compatible not of which usually are in older motorhomes. My charging systems will not do Lithium but will accommodate all others.

peedee

What folk don't realise is that when inverting up from 12v battery to (240v/230v) mains the amps are burning at 20 times the rate!...

this is why the battery bank needs to be substantial AND/OR the solar array is large AND/OR the batteries can be taken far lower than normal....(lithium).

Your battery size will dictate how long it can support the microwave use....not whether it will run, this will be down to the inverter.....it's size, output and, perhaps, if it's pure sine wave or not.

remember, a microwave start up current draw might be three times the size of the rated value.

Not just the size, as inverter does an error tone after only about 30 seconds.  Then cycles on/off with error.  4kW inverter (Chinese watts and sine wave) and an 800 watt microwave but it will run Truma space heat and water heat without complaint.  Going to try a 3kW kettle to load it up and see what happens.

Runs hair dryer, heated rollers and curling tongs so I am still a good guy.

My 700w microwave pulls 68A whilst it's running. Only a lithium or a very big conventional battery bank will cope with that sort of draw. I try to encourage OH not to produce too many chicken "ding" meals.

"My 700w microwave pulls 68A whilst it's running."

agreed...but an 1800w Truma system will pull 150A!

If you haven't set fire to the camp site beforehand, your 55A (the usable half of your battery's capacity) would last just 20 mins....

how have you connected a caravan's built in Truma system to an inverter?

as for a 3kw kettle....yes, folk do try these things (surely a gas kettle is the way?) but that kettle will draw 250A!!
That requires some real thickness of cable (95mm sq according to the look up I've just done..)

don't do it....

when top line MH get fitted with large inverters and auto switch over systems, some elements are deliberately NOT switched over for very good reason.... eg heating system...

these are only run on 'leccy' when an EHU is available...if not, it's gas NOT an inverter. ive never heard of a Truma system running from an inverted 12v source.

CY...I was just quoting your bit of the above....I wasn't suggesting you would set fire to any campsite, lol......😂

..but Nav, that's a huge amount of juice and it doesn't sound like a very common thing to be doing...and, believe me, I've been doing plenty of reading on this topic of late...

Well, an 800 Watt microwave is going to draw maybe 5 amps at 230 volts but also there is a current surge at switch-on. 5 amps at 230 V is around 100 amps at 12 volts but inverters are not that efficient so you need more than that. Not impossible but it needs a beefy battery and large cables. I have had problems in France with the microwave tripping the EHU because of the inrush current.