Divide watts by volts to get amps. So those 1200 watts require 5 amps at 240v or 100 amps at 12v. Then there are some losses in the conversion process by the inverter, and cable losses as well. So 1200 watts powered from your batteries may draw 110-120 amps. That is the total capacity of one of your batteries if run for an hour.
But it gets worse in 2 ways.
Battery specs are ususally based on the 20 hour discharge rate, and discharging them a lot faster means substantially reduced capacity. Secondly if the discharge rate is high, as in your case, the voltage will fall rapidly, which increases the amps. But the inverter low voltage cutout will probably trip well before running the batteries out.
So you will not get anything like 1 hour out of your pair of batteries. Then of course you need to replenish those batteries with solar or other means.
-- Edited by Are We Lost on Tuesday 18th of October 2022 06:22:45 PM
A simple way to factor in inefficiencies is instead of dividing the watts by 12v to get amps. Is to divide by 10.
So 1200 watts / 10 = 120 amps
For normal running down lead acid batteries, you really need to stick to 50% discharge. But if you go a lot more say once a month that's ok, but always charge batteries up asap. You also need capacity to charge up the batteries quickly.
As already pointed out if you draw a high current from the batteries they have a far lower effective capacity. So together with your 50% of the battery capacity you don't want to use regularly, you will chew up capacity very quickly.
Look for the data sheet for your battery.
Double or triple your battery capacity (wire together correctly, another issue) so each battery has a fraction of the load. Much kinder on each battery.
If it's a kettle get a Birko 750 watt kettle. Ok it will take longer to boil water but 750 watts is a lot kinder than 1200 watts.
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50L custom fuel rack 6x20W 100/20mppt 4x26Ah gel 28L super insulated fridge TPMS 3 ARB compressors heatsink fan cooled 4L tank aftercooler Air/water OCD cleaning 4 stage car acoustic insulation.
Thanks all
I was thinking of running a 1200w heater and I only have a 160w solar panel. We travel very day and was thinking it would give us enough time to recharge the batteries
As we only use the heater for an hour or so per day, I thought it would be a cheaper option than getting a diesel heater installed
But it looks like it might be hot water bottles and an extra layer of clothing for those frosty mornings
If you want to use an electrical heater on batteries your only real option is a 2.5kW domestic split system, say Daikin or Mitsubishi for example. The are about 500% efficient. Also use them on an economical setting.
You also need say 500AH minimum. Then over a kW of solar input to charge everything. So all this adds a lot of weight & your payload may already be on a knife edge.
Other options are a diesel heater & or insulation, simply covering windows properly makes a big difference.
Acoustic engine bay foam is great for thermal insulation on walls in hidden areas. But price does start adding up quickly.
A Sigg aluminium water bottle in very thick woollen sock works well as a hot water bottle. They never leak.
__________________
Procrastination, mankind's greatest labour saving device!
50L custom fuel rack 6x20W 100/20mppt 4x26Ah gel 28L super insulated fridge TPMS 3 ARB compressors heatsink fan cooled 4L tank aftercooler Air/water OCD cleaning 4 stage car acoustic insulation.
Thanks all I was thinking of running a 1200w heater and I only have a 160w solar panel. We travel very day and was thinking it would give us enough time to recharge the batteries As we only use the heater for an hour or so per day, I thought it would be a cheaper option than getting a diesel heater installed
But it looks like it might be hot water bottles and an extra layer of clothing for those frosty mornings
If in fact your current solar and charging system is adequate for what your travelling requirements demand then those diesel heaters are not that expensive if you buy one from the internet and maybe find a mechanic type person who would fit it for you. They arent difficult to fit.
This in most cases would be cheaper than upgrading the solar and batteries if only to run a heater.
There is another option is that you can buy a portable diesel heater that might be able to be used with a little bit of judicial modification to have it heat the van and be mounted outside.
I should point out that if you do choose a diesel heater then I strongly suggest the fitting of a C02 detector.
Indeed: *every* caravan should have a CO detector - Bunnings $30.
An Ebay diesel heater is about $180 for the complete kit, as said, they are not hard to fit but if that's not your thing I'm sure you could find a handyman who would fit it for, guessing, $300 to $400.
Diesel heaters are *marvelous!* - I actually carry a complete spare heater in case mine fails and even with the current price of diesel they are still very cheap to run.
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Thanks all I was thinking of running a 1200w heater and I only have a 160w solar panel. We travel very day and was thinking it would give us enough time to recharge the batteries As we only use the heater for an hour or so per day, I thought it would be a cheaper option than getting a diesel heater installed
But it looks like it might be hot water bottles and an extra layer of clothing for those frosty mornings
Ok a diesel heater as suggested by others or as in your own words, you travel everyday, drop down to a 1000w fan heater with a thermostat control and unless you already have one a DC to DC charger. Your heater will not need to run for an hour to heat up the van, but then when you drive the DC to DC charger will recharge your batteries along with the solar panel.
Obviously if you intend to stay longer than one night with frosty mornings then you will need to replace the energy that you use, therefore an additional solar panel on the roof and/or a portable solar panel will help.
Just for reference my 2000w Euromatic ceramic heater uses 1560w on high and 820w on low.
Tim
-- Edited by TimTim on Wednesday 19th of October 2022 10:51:08 PM
Not to forget your normal loads like fridge etc. Let's say 30AH.
So 100AH for the heater plus 30AH, about 130AH to recover.
We tend to drive most days but about 2 hours is our limit. Our car has a 180 amp alternator. Let's say you have 40 amp DC-DC, that's a fair load.
I would add a third battery to, that will share the stress considerably.
You need more solar, at the very least another 160 watts, better another 320 watts. Not to forget that flat on the roof it's not square to the sun often, so fairly unproductive. So you need as many watts as possible.
Wiring from the alternator. Let's say a 12 metre run, so that is 24 metres in total for + & - so let's say your 40 amp DC-DC charger is typi running at 30 amps. Ideally you want wire of 2awg (33mm2) 0.38 voltage drop. 4awg (21mm2) 0.6 voltage drop.
Payload! All the above adds up, let's say very roughly an additional 80kg.
__________________
Procrastination, mankind's greatest labour saving device!
50L custom fuel rack 6x20W 100/20mppt 4x26Ah gel 28L super insulated fridge TPMS 3 ARB compressors heatsink fan cooled 4L tank aftercooler Air/water OCD cleaning 4 stage car acoustic insulation.
Thanks all I was thinking of running a 1200w heater and I only have a 160w solar panel. We travel very day and was thinking it would give us enough time to recharge the batteries As we only use the heater for an hour or so per day, I thought it would be a cheaper option than getting a diesel heater installed
But it looks like it might be hot water bottles and an extra layer of clothing for those frosty mornings
Hi aastek
Here is a heating alternative we use. A 12V plug in throw rug. Cheap and easy and you can use it on the bed too. Sure not as nice as a 1200 W electric heater but easy to use, nil installation cost and low power use, 45W. My advice is to avoid ones with fancy controllers as they are more likely to fail. Actually we use 240V ones at home too and can use them in the MH with the inverter.
In the documents for my vans water heater it mentions that there is an option to include a van heater. It uses an extra hot water tank. The extra tank also increases the amount of hot water available for the van. I don't know if the van heater runs on the battery as well as gas.
I have an Ecotherm heater in my van installed by the previous owner. It does not have it's own tank but a pump circulates water from the water heater. This warms a radiatior like a car heater and a fan blows over that.
It's OK but I would not recommend it. I have never measured the gas usage, but the gas cycles on quite frequently. After hearing all the positive stories about diesel heaters I installed one. Like chalk and cheese and diesel is easier to replace than LPG.
Jaahn proposed a 12v throw rug. I have one of those, but no longer used. But a domestic electic blanket to pre-warm the bed works really well. I can't recall the watts now but probably about 75 watts per side on full heat. Running it for half an hour makes the bed quite toasty and not a huge drain on the battery.
.
