Battery or inverter?

[BryanM]

After my last query re extra solar power, I have gone ahead and ordered a 215 watt panel with a Victron MPPT controller. Ultimately the plan is to go skiing with the Motorhome so I have always thought a backup heat system to the gas fire would be good idea so I also ordered a 750/1500 watt Swiss Luxx ceramic heater ( turns out 1000/1500 watt when it arrived!). We have one of their low wattage toasters and it is great.

Solar panel not here yet but thought I would try the heater with what we have. 2 fresh 110 amp batteries, 100 watt solar and 1500/3000watt pure sine wave inverter. Batteries are showing as full on van indicator and full at 12.8 volts on the solar regulator but the heater on the lowest 1000watt setting only ran for about 5 minutes before the inverter started cutting out and restarting momentarily. Check the battery gauges and both still showing as full.

I bought the inverter a while ago and I can’t remember where I bought it from but it is mounted close to one of the leisure batteries with a short cable run and appears to be of German manufacture. Can they go on the blink but still partially work or am I missing something more obvious?

Hopefully should be showing a picture of the inverter.

 

[PeterCarole29]

There will be someone who will give you all the tech soon but remember liesure batts lead acid you should only drain down to 50%
on a regular basis

 

[Stealaway]

At a 1000 watts that heater is pulling over 100amps out of the battery.
It wouldn't take long to pull the voltage down to where the inverter voltage is too low.
You need more batteries

 

[funflair]

As above electric heating and batteries are not really compatible, certainly not with just 220ah.

 

[Richard n Ann]

You need hook up to heat the van electrically, or use gas.

Even if you've got a rack of leisure batteries you'd still need a large charging capacity.

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[jopparocks]

Have you considered getting a diesel heater. You can get them for £100 on ebay and are extremely effective.

 

[Itsmcb]

As mentioned above, 1000 watts is about 120amps once you factor in inverter loss. Your battery voltage will be dragged down in minutes causing your inverter to fluctuate. The batter voltage recovers just as quickly which is why they still register as full. As someone else mentioned a diesel heater is the way to go for backup. I've just finished fitting mine, also with skiing in mind. Another consideration is the short daylight hours and possible cloud which will seriously affect the output from your solar and therefore your ability to top up your batteries. 1kw of heating will struggle to keep your van warm in alpine conditions, a diesel heater can output 5kw

 

[DBK]

There is no way you can run an electric heater off solar especially in winter when the sun is low and daylight short even if you had lots of batteries as it would take days to recharge them.

But to work out why the heater only worked for five minutes you could try repeating the experiment but monitor the voltage at the batteries when it starts cutting in and out. I suspect the inverter was switching off because the supply voltage was too low. Once you turned it off the batteries recovered.

An inverter is a useful extra for running hair dryers and coffee machines but forget trying to heat the MH using one.

 

[jumar]

Being off grid during the winter is quite challenging, especially at ski-resorts...the low sun, the fresh snowfall all skiers dream of can be very detrimental to motorhome use. Your Solar could get snow cover as well as the piste....
Hook up would be the way to go in my opinion..

 

[autorouter]

You say you have two 110Ah batteries, what type are they (flooded, sealed, AGM, Gel etc)? Some types like Gel are not very good at high amps, and are better at low amps for long time.

The maximum discharge rate for lead-acids generally is about C/5, where C is the battery capacity. So for 220Ah of battery capacity the maximum discharge should be 220/5 = 44 amps.

People get away with higher amps for short times, for a coffee machine or microwave for example, but a 1kW heater is not really sustainable from those batteries.

Note that you can find the energy capacity of the battery from its charge capacity by multiplying by the voltage. If the charge capacity is 220Ah, then the energy capacity is 220 x 12 = 2640 watt-hours, ie 2.64kWh.

Since it's recommended that the battery is only discharged to about 50%, that means you only have 1320 watt-hours of usable energy. For a 1000W heater that is only going to last about an hour anyway. Electric heating from batteries is really not a great idea.

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[Itsmcb]

Hook up or join the Genny club. Or, invest in an Efoy.
Edit: this a reply to post #9

 

[funflair]

Hook up or join the Genny club. Or, invest in an Efoy.
Edit: this a reply to post #9

EFOY would be good for keeping a basic charge in the batteries and keeping stuff ticking over but even the biggest which I think is rated at 8A would only put about 100 watts in per hour so it's not going to sustain 1kw draw, I don't think you were suggesting it would but just mentioned for clarification

 

[Mixyblob]

A good rule of thumb is
If an electrical appliance's primary function is to provide heat, it shouldn't be using 12vdc.

 

[BryanM]

Thank you for all your replies. I’m obviously expecting too much from my batteries .
Will go down the diesel heater route if I think it’s necessary, I fitted one in my garage, but will hold fire until next year as flying to the slopes this season.
The system in it is ideal as it is a gas fire so can run all day using no battery power unlike the modern blown air systems, but has a couple of fan systems to heat the toilet or front cab if wanted. Whoever specced the van in ‘98 was keen on extras as they had ticked the factory fitted 64litre lpg tank so plenty of capacity.

 

[Hoovie]

Space Heating off Batteries is never viable. The only time you would stand a chance doing that is if you had a big solar array and a nice clear long sunny day - and in those situations, it is maybe unlikely you actually need space heating

Ref battery bank sizing and inverter use, I often read these "you need x amount of Ah to run y Watts off an inverter" and TBH I really don't agree with them. Yes, the bigger the battery bank the better, but it is not a matter of you cannot do it. I ran perfectly successfully a 2kW Hot Water Heater and a 2kW Induction Hob (not at the same time of course) off initially a 400Ah AGM battery bank.
That is over 200A and the perceived wisdom of this forum would have me having a minimum of a 1000Ah battery. I later upgraded to a 645Ah AGM Battery bank, but only as I could get the batteries at a very good price (I sold the 4 100Ah ones at close to the cost of the 645Ah bank). Even this 645Ah bank should have been too small (luckily no one told the Hob or the Water Heater ).

Running a 1000W load and having the inverter cut out after 5 minutes sounds like voltage issues, but I wouldn't automatically assume it is a battery voltage issue. You need to get a meter on the battery and see what the voltage is when it cuts out.
That Inverter is extremely unlikely to be of german manufacture anymore than an inverter with English writing will be of British Manufacture. It is a typical Chinese-made, Chinese-design inverter labeled for the German Market I would say ("Spannungswandler" is not a brand, it is the german word for "inverter"). If you are using cables supplied with it, how thick are they? how flexible are they? if they are typical cables supplied with mid-range to cheap inverters, they will be both undersized and made of aluminium and will suffer high voltage loss.

The last inverter I installed was a fortnight ago. It was a 1000W inverter (Victron 12/1200) and I used 35mm pure copper cables for minimal voltage drop. customer used it today with an Induction Hob he just bought, on his single 100Ah Lithium Battery. At 800W the voltage dropped to 12.3V; at 400W the voltage dropped to 12.8V. Both perfectly acceptable levels for the load - and it also demonstrates you don't need a massive battery bank for an inverter. Cabling is a very important aspect - and is not just about ampacity but about voltage.

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[cyberyacht]

I'd have thought that without lithiums it's a complete non-starter. Even with lithiums it's a big ask. As others have suggested LPG or diesel is the way to go for winter warming as an alternative to EHU.

 

[BryanM]

Space Heating off Batteries is never viable. The only time you would stand a chance doing that is if you had a big solar array and a nice clear long sunny day - and in those situations, it is maybe unlikely you actually need space heating

Ref battery bank sizing and inverter use, I often read these "you need x amount of Ah to run y Watts off an inverter" and TBH I really don't agree with them. Yes, the bigger the battery bank the better, but it is not a matter of you cannot do it. I ran perfectly successfully a 2kW Hot Water Heater and a 2kW Induction Hob (not at the same time of course) off initially a 400Ah AGM battery bank.
That is over 200A and the perceived wisdom of this forum would have me having a minimum of a 1000Ah battery. I later upgraded to a 645Ah AGM Battery bank, but only as I could get the batteries at a very good price (I sold the 4 100Ah ones at close to the cost of the 645Ah bank). Even this 645Ah bank should have been too small (luckily no one told the Hob or the Water Heater ).

Running a 1000W load and having the inverter cut out after 5 minutes sounds like voltage issues, but I wouldn't automatically assume it is a battery voltage issue. You need to get a meter on the battery and see what the voltage is when it cuts out.
That Inverter is extremely unlikely to be of german manufacture anymore than an inverter with English writing will be of British Manufacture. It is a typical Chinese-made, Chinese-design inverter labeled for the German Market I would say ("Spannungswandler" is not a brand, it is the german word for "inverter"). If you are using cables supplied with it, how thick are they? how flexible are they? if they are typical cables supplied with mid-range to cheap inverters, they will be both undersized and made of aluminium and will suffer high voltage loss.

The last inverter I installed was a fortnight ago. It was a 1000W inverter (Victron 12/1200) and I used 35mm pure copper cables for minimal voltage drop. customer used it today with an Induction Hob he just bought, on his single 100Ah Lithium Battery. At 800W the voltage dropped to 12.3V; at 400W the voltage dropped to 12.8V. Both perfectly acceptable levels for the load - and it also demonstrates you don't need a massive battery bank for an inverter. Cabling is a very important aspect - and is not just about ampacity but about voltage.

Had a quick look at the cables and they are 7.5 mm but can’t see if they are copper or not but would suspect not. 35 mm copper cable seems huge but if that is likely to make a difference I can get them made up easily enough. Would certainly like it to make a difference as my wife would love our 1200 watt air fryer to perform!

 

[Raul]

The only way I would use electric for heating is aircon on heat mode ( air to air heat pump). That way I can turn it up gradually if needed, and have a cop 3 at least. Resistance heating with inverter is expensive.
In your case, diesel heater is your friend. One litre can last the hole day even in fairly cold days.

 

[rob0114]

Hi,

Go skiing every season with our diesel heating equipped van - Truma 6DE.

Have had temps of down to -25degs at night & for a week used less than a quarter tank of fuel (60L tank).

Wouldnt use the hook up as most winter campsites are metered for obvious reasons!

Would thoroughly recommend a diesel heater - just make sure you fill up near a ski resort for 'mountain diesel'.

Cant help re your inverter issue but hope the above helps!

 

[Raul]

Had a quick look at the cables and they are 7.5 mm but can’t see if they are copper or not but would suspect not. 35 mm copper cable seems huge but if that is likely to make a difference I can get them made up easily enough. Would certainly like it to make a difference as my wife would love our 1200 watt air fryer to perform!

I would guess you got 16mm2, you need minimum 35mm2 for 1/2m run, or better 50mm2.
Victron 12/2000va requires 70mm2, that’s why I say 50mm2 for 1500w plus inverter loses. If you don’t exceed 1000-1200w you can get away with 35mm2 but short and fused at source anyways.

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[autorouter]

Had a quick look at the cables and they are 7.5 mm but can’t see if they are copper or not but would suspect not. 35 mm copper cable seems huge but if that is likely to make a difference I can get them made up easily enough.

To avoid any misunderstanding, cables are specified usually by their cross-sectional area (CSA) in square millimetres (mm2), not their diameter. So 35mm2 cable has a diameter of about 12mm, and 16mm2 cable has a diameter of about 7.3mm.
There's a table here

Cable size table | 12 Volt Planet

A guide on cable sizes from 12 Volt Planet

www.12voltplanet.co.uk

To add to the excitement, very often they miss the '2' off the 'mm2'

If you have some 16mm2 cable it can be doubled up to make 32mm2, what matters is the total CSA of copper, it doesn't matter if it's in separate wires.

 

[BryanM]

Now have the new solar panel and mppt controller fitted and all seems well.
Next issue was the battery to inverter cable and I went up this afternoon to my local auto electrician to get ones made. Note to self don’t ask favours on a Friday afternoon! Anyway although too busy to make exactly what I wanted, did give me the attached two cables which he said would do the job. The cables are 60mm2 each so 120mm2 per lead. My query is should I cut one of the cables off so it is just a single 60mm cable or just leave them as they are?

 

[Richard n Ann]

You could connect to both batteries directly with those