Tropdoug wrote:

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Hi guys, I know there are a heap of posts regarding solar, but there is so much information in different ways my old head is spinning. So, can someone confirm or correct me please.

[1]If I have a 240V appliance running for 5 hrs at 7.5Amps max - I would be consuming 37.5 A/hrs of power -- is that correct?

If I add a second 240V appliance consuming 3 Amps but run only for 10 minutes a day then that appliance would consume 0.5 A/Hrs

The two appliances would then need 38 A/Hrs of power to run.

[2]If that is correct, then I need a solar panel (or other method) capable of recharging my battery bank on a cloudy day, that 38 A/hrs of power.

[3]On top of this I would need to add on all the 12V power draw and the inverter as well?

I am using only two hypothetical appliances here just to make it simple for my brain. I can add up the totals once I know if I am doing this right.

 

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 Hi

[1]Yes, that is the correct way of calculating the Ahrs used

[2]Now you have to do the reverse

[a] if solar you have to work out how many hours per day the solar will be producing" x "amps, so that hrs of solar X by solar" A" output gives you your 35Ahrs

Plus a margin of about 20<30% for losses in the charging of the battery.

Then you need to consider cloudy rainy days & how you will replace the charge in those situations

 

That could be a combination of more battery capacity & more solar

OR a generator & charger

The inverter will have efficiency losses, so any time that is used those losses also have to be taken into account.

See how you go & come back if needing  more hep

 

PeterQ

Hi guys, good to see you again Peter and Dave,

Inverters are going to always be an issue for us. I tend to think that they are ok for low to medium wattage appliances, reason I say that is, the higher the wattage the appliance is the more current drawn from the battery thus the need for a bigger heavier battery bank.

IMHO, the inverter should never drain a battery quicker than overnight, let's face it, in the cold you want to be warm so we have 150W electric blankets hooked up to our inverter, most mornings the inverter tells me the batts are at low voltage and should be charged, this is after using lighting, TV etc during the night.

I also use my inverter for small appliances and charging my laptop and phone when needed. I believe the idea of running aircon and other heavy drain appliances is crazy, we start to get into realms of the total payload of the van being the multiple large batteries to keep the equally large and heavy inverter going. May as well get a good generator for the heavy work and inverter for what I have said above. 

Cheers guys

-- Edited by Phil C on Sunday 14th of June 2015 10:49:36 AM

Phil, why do you need a electric blanket mate ? I had heard you are hot in bed.

Mmmm, I'll take myself back to the naughty room. Sorry all.

I have Gene chained up in the back of the tug for when I need her help but that is very rare as I don't have big electric appliances. I set myself up for mainly 12v use or gas. Works for me anyway but I understand everyone has different needs and ideas.

Hmm, me thinks Doug might need more than cut lunch in the naughty room, especially if he takes Gene and her chain with him !

Phil, we will need to agree to disagree on this one, as you probably know I use my solar, battery, and inverter to run life's little luxuries in our van. Including such things as an all electric fridge, aircon (for many hour after the sun goes down), washing machine, microwave, induction cooker, hair dryer, etc. Now I am not for a moment suggesting that everyone should go down this route, or try to copy what we have with a standard van, it is only possible for us because the van was built to cater for what we want to do.

BTW, we do not have electric blankets, but we do have good winter quilts.

 

Troupdog, our setup is somewhat over the top, but we love it.

Solar

We have 1,200 watts of solar fixed on the roof in the form of 12 100w light weight panels, they are arranged in 3 strings of 4 panels delivering 68 volts to a 50 amp MPPT charger which feeds 200ah of Lithium batteries at a nominal 24 volts. This in turn cross charges the standard 12V AGM house battery through a 24v to 12V charger (on all the time). That looks after the 12 volt side of things, including the fridge.

Inverter

The 240 volt side is fed by a 3 Kw low frequency (translates to blood heavy) inverter which is permanently wired in. It feeds the van through a specialised safety switch called an RVD-EM (replaced the RCD). 

All sounds nice and simple, but the solar side took a fair bit of development (read trial and error) to optimize it. Similarly the inverter is sitting in a corner, and tends to get hot so it now has a new vent in the side of the van, and some temperature controlled fans just for it.

The whole setup has been certified, and that process lead to it being wired in a configuration that I believe is sub optimal, but it works.

Perhaps the best example of how well it works was last Christmas at Greens lake, after a big Lunch we retired to the van to rest, and we turned on our Fujitsu split system (mounted on the back bumper), we ran it till 5:30 when we returned to the group to have desert, at that point our battery was about 98% full, it had still been charging with the air running. We then returned early evening, and being stuffed like a Christmas turkey, and still hot outside we retired inside, and powered up the air con again. Five hours later we turned the air con off, and in the morning our main battery was still on 62% charge (lithium is OK down to between 20 and 30%).

The inverter happily runs all the items mentioned, however we do need to be careful with some as they are power hogs, any form of cooking (microwave, and induction), and the hair dryer are the ones that leap to mind.