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# New system needed

OP

#### Sooz52

Have you measured the space you have for batteries?thats where you need to start and do you have an inverter to charge your laptop
Hi, yes yes and yes

OP

#### Sooz52

The idea is not to exceed the voltage and current limits. For a 100/50 regulator, 100 is the voltage input from the panels, and 50 is the current (amps) output to the batteries.

If the panels are in parallel - as usual on motorhomes - the voltage will be the same as a single panel voltage of 20 to 40V, so voltage is never a problem.

To work out the current, take the nominal panel watts and divide by the BATTERY voltage, then take about 70 or 80% of this if in Europe with the panel flat on the roof.

Example: three 120W panels: 360/12 = 30 amps, 80% of that is 24 amps. So if the choice is a 100/20 and a 100/30, it would have to be the 100/30.

Don't be misled by the 'max power current = 5.45A'. That's the PANEL output current, at the max power voltage of 22.0V. When the regulator steps down the voltage to feed the battery, it steps up the current to keep the power (volts x amps) the same.

So a 100/30 regulator can manage about 400W of panel if feeding a 12V battery, but can manage 4 x 400 = 1600W of panel if feeding a 48V battery. That's one reason for using higher battery voltage on a house installation, where the only thing connected to the battery output is the inverter.
Thanks, really helpful. It looks like I need 100/50 with the set up Iâ€™m planning

OP

#### Sooz52

Ditch the gel and get half of that capacity in lfp. You donâ€™t need bmv 712, a 702 will suffice.
Itâ€™s just sooooo expensive!

#### Raul

Look at ultramax 480 quid for 100ah, bms inside. Whatâ€™s not to like? You can have as many as you like in paralel. They based in London, UK vat invoice, ebay shop free delivery mainland uk. Still expensive? I donâ€™t think so.

OP

#### Sooz52

Look at ultramax 480 quid for 100ah, bms inside. Whatâ€™s not to like? You can have as many as you like in paralel. They based in London, UK vat invoice, ebay shop free delivery mainland uk. Still expensive? I donâ€™t think so.
I am waiting for a call back from them, thanks (although I am in Spain)

OP

#### Sooz52

Ultramax 200Ah ordered!! Woohoo. I note that they include a charger so an MPPT isnâ€™t strictly necessary... Iâ€™ll leave my exiting MPPT on the old panels which will look after the car battery and also plug into the new battery. Do I really need another MPPT (victron 100/50) to manage my power effectively?

#### Raul

Congratulations, the charger that comes with it, if is a 20a charger it stops at 14.4v if is a 10a charger it stops at 14.6v to high. Note, these chargers are mains plug in. From the solar you still need a configurable MPTT or PWM. I do not use the main charger except for the first charge, there after I donâ€™t charge to full never. I stop charge at 13.70- 13.80v max. On ehu, I use the victron inverter charger to charge from mains, limited to 0,2C rate. On your 200ah you can charge up to 40a rate, to keep it sweet. I got two of those in the picture, paralleled with a 100a blue sea cube fuse on terminal and 35mm cables.

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OP

#### Sooz52

It is with a large touch of embarrassment I post this. I was going through the fuses checking why my wardrobe and above passenger seat lights arenâ€™t working and found that the fuse labelled â€śsolarâ€ť had blown. Can anyone tell me what function this fuse serves in the solar set up? Possibly Iâ€™ve only been getting charge from the alternator... Separate tests in 2 workshops have told me my batteries are pooped anyway so the new lithium is going to be fab.

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#### Rodneyplonker

Any fuse in the system is a safety device against damage to the system. For instance, if working on your batteries or disconnecting them. Iâ€™m sure damage to your regulator and even the panels could occur if the charge from the panels was not disconnected when removing or disconnecting the batteries. your system should be checked to find the cause of a blown fuse...if not immediately obvious. Obviously, if not running the engine your batteries would soon flatten if no current getting to them because of blown fuse.
Members with greater knowledge will expand on this, Iâ€™m sure.

#### autorouter

Can anyone tell me what function this fuse serves in the solar set up?
A fuse is a safety device. Any wire connected to a battery needs to have a fuse. If no fuse is wired in, then if the metal part of the wire touches the metalwork the battery is shorted, and the wire heats up until it is glowing red-hot and can easily start a fire. To avoid that, a fuse is wired in so that if the wire touches the metalwork, the fuse blows instead, and cuts off the battery current.

In your solar circuits, it depends on whether the fuse is between the solar controller and the battery, or between the solar controller and the panels.

On the battery side it is an essential safety device. On the panel side it is not really necessary because shorting the solar panels does not lead to excessive current like when you short a battery. But sometimes they are fitted anyway, and can be handy if for some reason you want to disconnect the panels from the controller.

You could try just replacing the fuse to see if the battery starts charging. If the new fuse blows there might be a wiring fault.

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OP

#### Sooz52

A fuse is a safety device. Any wire connected to a battery needs to have a fuse. If no fuse is wired in, then if the metal part of the wire touches the metalwork the battery is shorted, and the wire heats up until it is glowing red-hot and can easily start a fire. To avoid that, a fuse is wired in so that if the wire touches the metalwork, the fuse blows instead, and cuts off the battery current.

In your solar circuits, it depends on whether the fuse is between the solar controller and the battery, or between the solar controller and the panels.

On the battery side it is an essential safety device. On the panel side it is not really necessary because shorting the solar panels does not lead to excessive current like when you short a battery. But sometimes they are fitted anyway, and can be handy if for some reason you want to disconnect the panels from the controller.

You could try just replacing the fuse to see if the battery starts charging. If the new fuse blows there might be a wiring fault.
Thanks... though I know what a fuse does... the question was intended to be - in which part of the circuit does this fuse sit.

#### autorouter

Thanks... though I know what a fuse does... the question was intended to be - in which part of the circuit does this fuse sit.
If the fuse has blown it's almost certainly in the part between the controller output and the battery.