Safe battery load

[TheFrenchConnection]

The OH is a Remoska addict and we plan to take it with us on our winter Spain/Portugal trip this year. 

My 'O Level' physics tells me that its 400W is less than 2A, so it should be fine on any EHU. However if we wanted to use it on an inverter would that current draw be unkind to our (almost new) 110AH leisure battery?

We have a solar panel and would probably only be off EHU for a couple of days at a time.

Advice from more electrics-knowledgeable people would be appreciated.

able

[colin]

From AandN, Inverters (aandncaravanservices.co.uk)

That would indicate the max load for your battery should be limited to 264w, say 250 to allow for invertor losses.

[TheFrenchConnection]

Thanks Colin, that' a very useful link.

I'm a bit confused though as the 'five times' rule uses the load in amps multiplied by five to give the battery capacity in AH. So the load of the 2A Remoska x 5 = 100AH, just within a 110AH battery. The inverter would need to supply 2A x 230V = 460W (plus allowance for losses)?

I'm far from an expert here, am I missing something?

[Keithl]

But to get 2 A at 230 V would require a supply into the inverter of 2 * 230/12  or nearly 40 Amps!

Or look at it another way, you require 400 W at 230 V and Watts is Watts irrespective of voltage so add 10% for inverter losses and you need 440 W at 12 V or once again near 40 Amps!

You are going to need considerably bigger batteries to run your Remoska!

Keith.

[TheFrenchConnection]

Thanks, I knew I had to be missing something! Should have paid more attention in Physics!

[Brian Kirby]

8 minutes ago, TheFrenchConnection said:

Thanks Colin, that' a very useful link.

I'm a bit confused though as the 'five times' rule uses the load in amps multiplied by five to give the battery capacity in AH. So the load of the 2A Remoska x 5 = 100AH, just within a 110AH battery. The inverter would need to supply 2A x 230V = 460W (plus allowance for losses)?

I'm far from an expert here, am I missing something?

I think there may be a misunderstanding above.  The connected load is measured in Amps (A), which is not the same as Amp hours (Ampere hours, or Ah), which is the power consumed when a load of 1A is sustained for 1 hour.  The 5 times rule, as I read it, relates only to the connected load. 

However, Watts are Amps x Volts, so your 400W (but are you sure, as ours (quite old) is plated at 500W) Remoska will place roughly a 33A (plus a bit for inverter inefficiency - about which I know nothing!) load on a 12V battery.  Your battery has a capacity of 110Ah but, to avoid damage, should not be discharged below 60% of that capacity, giving you a usable 66Ah, or roughly 2 hours of Remoska use, assuming the battery is relatively new and is fully charged when you start cooking.

Four other things to bear in mind.

1) Unless they have redesigned the Remoska since we got ours (which is quite likely!) it will have no thermostat, so will draw a continuous 400W (66A) for the whole time it is cooking.

2)  Remoskas are slow cookers, and our experience (which may well reflect what we cook in it) tends to take about an hour to cook anything we put in it. 

3) You will probably have other things drawing power from the battery, contributing to the extent to which it will be discharged.

4)  What you take out you have to put back, and if the battery has been discharged to 60% of its capacity, to avoid damage the recharging process should not be delayed and should ideally be provided via an "intelligent" type charger - meaning via the mains charger rather than from the vehicle alternator.

So I think what I'm saying, as a non expert, is that I think your Remoska  risks giving your battery a caning it will not greatly appreciate - especially if you are contemplating using it while being "off grid" for two days at a time.  However, just my non expert opinion - so I'll be interested to see what the real experts have to say. 🙂 

[witzend]

We also have a Remoska and use it at home and when on ehu and away in the Van. But when away we mostly use a Double Skittle.

https://tinyurl.com/mvp8wbmv

[Barryd999]

Without considering all the calculations I would have said a 400w continuous load on a single 110ah battery was battery suicide.   The guys on the wildies forum are often talking about this kind of thing but they are sitting on banks of really powerful Lithium batteries and 2kw invertors.   Most power hungry thing I run off our single 120ah AGM battery (Which is superb by the way) is a laptop which when ticking over is about 12 watts. (max about 45 if charging) or the TV, 14 watts or maybe 17 with usb speakers in.

You need a big lithium set up for this kind of stuff. Keep it 12v if on a single lead acid battery.

[Steve928]

I find that converting battery capacity to Wh (watt-hours) is a simple method, for example:

- a 100Ah lead-acid battery can only be discharged to 50% without serious impact on its already short cycle life so 100/2*12V = 600Wh of usable power (say 1.25 hours of Remoska + inverter overhead).

- a 100Ah LifePo4 battery, which can be fully discharged, contains 100*12.8V = 1280Wh.

It brings home how little capacity even a double 100Ah LifePo4 setup has compared to EHU i.e. approx. equal to 2.5 units (KW/h) of grid electricity.

[laimeduck]

OK  can I ask another questions related.

I have a 100 watt crockpot which I use with an inverter from the habitation 12V supply while we are driving.

I have 2 x 110 Ah leisure batteries.

So on your formula I should have 110/2*12V = 660 Wh so for 2 batteries *2 = 1320Wh (or ~ 12-13 hrs)

But these batteries are presumably being charged by the alternator when we are driving, so I assume I am not using the batteries Wh that much? (.....or it's being replenished by the alternator?)

Am I correct here?

I know it works, but I want to be sure I'm not clobbering the batteries.

The big problem we have is the Pavlov pouch effect  inducing aromas that emanate from the crockpot as we drive!

Jeremy

[colin]

I don't see a 100w load being a problem, but if you where going (a lot) higher you would need to consider if you where putting too much load on your charging system. Take my van, the EBL99 has a 18amp charger, if this was having to charge 'flat' batteries and power a load it might start to struggle.

[Aethelric]

Your alternator can almost certainly cope with an extra 100watts. That is less than your headlights take. If you are worried about your charging system then you can plug your inverter into the cigar lighter socket.  These are usually rated at 120W. 

[weldted]

My reckoning is to get1amp @ 240 volts a.c. You need around 26 amps @ 12 volt d.c. allowing for inverter inefficiencies and voltage cable loss. The trouble with running an inverter from the hab batteries when driving is often the cables to carry the charge to the hab batteries is often undersized fro the job so reducing current. On our 2012 Elddis Aspire I ran our 2000 w inverter from the engine battery, so whilst driving it go the full charge from the alternator. I could also run the microwave for up to 20 mins and still leave enough power for starting the engine.\we now have a Burstner where I have 700 watts of solar panels, 2 x 100 amp ‘Transporter batteries and a Victron 12/2000/80 inverter charger. We can run our Freshjet 2200 from this when parked up for around 4/5 hours when the sun is shining and not trying to turn the van into a fridge. But with any heavy power use you only get out what you put into it.