inverter question

[mark2310]

Hi

I need help with a problem.
At the moment the system im building has 2X 235watt panels at 37v each.
A 40 amp MPPT.
One 110 ah 12v battery.
A 12v 1000w inverter.

I know I will need more batteries.
Is it possible to run a 12v inverter from a 24v system. (I think it will be 24volt because of the panel input)
or is it possible to charge a 12v battery from the panels that I have.

Thanks
Mark

[foo1bar]

I think you have this in the wrong section.
I'd suggest asking a mod to move this thread to the "off-grid" section.
(and the mods can feel free to delete my post if they do move it)

[inetdog]

Hi

I need help with a problem.
At the moment the system im building has 2X 235watt panels at 37v each.
A 40 amp MPPT.
One 110 ah 12v battery.
A 12v 1000w inverter.

I know I will need more batteries.
Is it possible to run a 12v inverter from a 24v system. (I think it will be 24volt because of the panel input)
or is it possible to charge a 12v battery from the panels that I have.

Thanks
Mark

It is not possible to run a 12V inverter from a 12V battery bank.
It is possible to charge a 12V battery from a 37V panel, or two 37V panels in series. That is the job that the MPPT inverter is made for.
As a practical matter, which you should have looked at before buying the 1000W inverter, 1000W is too large to drive comfortably from a 12V battery. The DC wiring is large and sensitive to bad connections at that amperage (around 100A.)
You can keep the panels and the CC and go to four six volt batteries in series to make a 24V 200AH system. But you will have to change the inverter.

[mark2310]

It is not possible to run a 12V inverter from a 12V battery bank.
It is possible to charge a 12V battery from a 37V panel, or two 37V panels in series. That is the job that the MPPT inverter is made for.
As a practical matter, which you should have looked at before buying the 1000W inverter, 1000W is too large to drive comfortably from a 12V battery. The DC wiring is large and sensitive to bad connections at that amperage (around 100A.)
You can keep the panels and the CC and go to four six volt batteries in series to make a 24V 200AH system. But you will have to change the inverter.

Thanks for the info.
So it is possible to charge a 12volt battery from the 2 37volt panels I have through the MPPT.
So can I increase the number batteries to power the inverter then at a later date change it to a 24v set up?

Thanks again
Mark

[Mike90250]

Moved to the off-grid area

At the moment the system im building has 2X 235watt panels at 37v each.
A 40 amp MPPT.
One 110 ah 12v battery.
A 12v 1000w inverter.
I know I will need more batteries.
Is it possible to run a 12v inverter from a 24v system. (I think it will be 24volt because of the panel input)
or is it possible to charge a 12v battery from the panels that I have.

First, you need a 24V inverter to run off of a 24V battery bank. A 12V inverter will die very quickly

Your MPPT controller should be able to convert your panel voltage to 12V with little loss, if it IS a true MPPT.

A 1,000 watt inverter will only run at full power off a single 12V battery. It's idle power will be about 100w just sitting there. That's a lot of inverter, and I suspect you will do much better to use a smaller inverter sized to your loads

Loads - what are you consuming ? That will set the size of the battery bank, and that sets the voltage and amperage of the whole system. The panels you have will only support 500w of daytime loads, so a larger inverter would be wasted.

[mark2310]

Moved to the off-grid area


First, you need a 24V inverter to run off of a 24V battery bank. A 12V inverter will die very quickly

Your MPPT controller should be able to convert your panel voltage to 12V with little loss, if it IS a true MPPT.

A 1,000 watt inverter will only run at full power off a single 12V battery. It's idle power will be about 100w just sitting there. That's a lot of inverter, and I suspect you will do much better to use a smaller inverter sized to your loads

Loads - what are you consuming ? That will set the size of the battery bank, and that sets the voltage and amperage of the whole system. The panels you have will only support 500w of daytime loads, so a larger inverter would be wasted.

Hi

Thanks again for the info.
Is it not possible to use the inverter with more batteries wired in parallel?

My use for the set up will be to run my caravan and I intend to build the system to be mobile on a small trailer so all items will have a sort cable run except for the connection to the van. This will be from the inverter to the van 240v AC.

I hope what im trying to say makes sense.

Thanks
Mark

[Mike90250]

Read this article about batteries in parallel. More than 2, and complications start to build up.

http://www.smartgauge.co.uk/batt_con.html

(hmmm. their site is quite slow tonight)

[SunEagle]

Hi

Thanks again for the info.
Is it not possible to use the inverter with more batteries wired in parallel?

My use for the set up will be to run my caravan and I intend to build the system to be mobile on a small trailer so all items will have a sort cable run except for the connection to the van. This will be from the inverter to the van 240v AC.

I hope what im trying to say makes sense.

Thanks
Mark

Running a 240volt AC unit from batteries through an inverter is very costly based on the size of your battery system needed and inefficiencies of the inverter.

[mark2310]

Running a 240volt AC unit from batteries through an inverter is very costly based on the size of your battery system needed and inefficiencies of the inverter.

Thanks again to all that have replied.

I guess I need information on how to proceed with the items I have. I still need to purchase batteries. (any ideas) I've read the link supplied above thanks.
The items I will be running of the set up will be.

A fridge rated at 150 watts.
Small amount of Led lighting. 20 watt max.
Microwave 800 watts.
Fan 35 watts.

Mark

[Bucho]

At the moment the system im building has 2X 235watt panels at 37v each.
A 40 amp MPPT.
One 110 ah 12v battery.

What battery are you using because you're charging it at something like c/3

[mark2310]

What battery are you using because you're charging it at something like c/3

Hi

The system is not yet built im looking for info and checking what I have will work.
I need to buy batteries but I have a 12v 110ah battery kicking around at the moment, sorry if this has lead to any confusion.

So to recap.

2x 235 watt panels at 37v
MPPT 40 amp
12 Volt 1000 watt inverter (Brought over a year ago before I thought of doing this)
12v 110 ah battery ( well forget about the battery)

I would like to run a fridge in my van at weekends or for a week if I stay longer. (may run this on 12v)
Led lights 20 watts max.
Fan 35 watts
Microwave 800 watts

Info on the type of batteries and numbers would be helpful as I think most of my questions have been answered.

Thanks again to all for the info so far.
Mark

[SunEagle]

Hi

The system is not yet built im looking for info and checking what I have will work.
I need to buy batteries but I have a 12v 110ah battery kicking around at the moment, sorry if this has lead to any confusion.

So to recap.

2x 235 watt panels at 37v
MPPT 40 amp
12 Volt 1000 watt inverter (Brought over a year ago before I thought of doing this)
12v 110 ah battery ( well forget about the battery)

I would like to run a fridge in my van at weekends or for a week if I stay longer. (may run this on 12v)
Led lights 20 watts max.
Fan 35 watts
Microwave 800 watts

Info on the type of batteries and numbers would be helpful as I think most of my questions have been answered.

Thanks again to all for the info so far.
Mark

Knowing how many watts each load is only half the answer. How long are you going to run each item on a daily basis. From that you can calculate the watt hours and then add them up to size your battery system.

Fridge @ XX watts * y hours = z watt hours
Lights @ 20 watts * a hours = b watt hours
Fan @ 35 watts * c hours = d watt hours
Micro @ 800 watt * f hours = g watt hours

z + b + d + g = daily watt hours.

[mark2310]

Knowing how many watts each load is only half the answer. How long are you going to run each item on a daily basis. From that you can calculate the watt hours and then add them up to size your battery system.

Fridge @ XX watts * y hours = z watt hours
Lights @ 20 watts * a hours = b watt hours
Fan @ 35 watts * c hours = d watt hours
Micro @ 800 watt * f hours = g watt hours

z + b + d + g = daily watt hours.

Ok

I know have a total of 4020 watt hours.
Do I need to multiply by something to get the battery size?

Thanks

[SunEagle]

Ok

I know have a total of 4020 watt hours.
Do I need to multiply by something to get the battery size?

Thanks

That is a lot of energy to run from batteries and will be costly.

If you are going to use 4kWh daily then you will need a battery 5 times that so that you will not discharge it more than 20% a day and have a couple of days of power if the sun isn't shining.

So 4000 x 5 = 20000watt hours.

That is big so you should be looking at a 48 volt battery system. 20000 wh / 48 v = 417Ah. So you need to build a system of batteries that consists of 24 x 2volt 400Ah or 12 x 4volt 400Ah batteries.

Your panel wattage will be around 2000 watts and you will need a 40A MPPT charge controller.

Are you starting to understand the costs to run your electrical loads? You might want to rethink what to run and what not to.

[mark2310]

That is a lot of energy to run from batteries and will be costly.

If you are going to use 4kWh daily then you will need a battery 5 times that so that you will not discharge it more than 20% a day and have a couple of days of power if the sun isn't shining.

So 4000 x 5 = 20000watt hours.

That is big so you should be looking at a 48 volt battery system. 20000 wh / 48 v = 417Ah. So you need to build a system of batteries that consists of 24 x 2volt 400Ah or 12 x 4volt 400Ah batteries.

Your panel wattage will be around 2000 watts and you will need a 40A MPPT charge controller.

Are you starting to understand the costs to run your electrical loads? You might want to rethink what to run and what not to.

So the problem is the fridge running 24hrs at 150 watt burning 3600wh.
It wont be running all the time so I need to figure out how much power it takes over 24 hrs.

Mark