Quality Solar Charge Controller for 123W Panel and LiFePo4 Battery..?

[James130]

Hello All

I hope someone is able to advise me on my 1st post, and please correct any incorrect assumptions I have made.

I have an old Land Rover Defender 130 camper van which has been happily running a 123W (12v) solar panel going through a simple MorningStar PWM charge controller to 2 lead acid batteries with a total of 130Ah capacity.

Due to age and excessive discharge the batteries now need replacing.

Despite the relatively high initial cost, I rather fancy the Polinovel LiFePo4 deep cycle batteries to give me significantly more usable Ah capacity in the limited space available. They have some BMS built in, but does not include the all important charge cut-off at under 0 to +5 degrees C temperature to avoid damage.

So, I thought what might suit would be a Victron SmartSolar MPPT 75/10. Add a Victron Smart Battery Sense to show temperature and use the VictronConnect app to set the charge to cut-off at under 5 degrees C - will this set up work OK ?

But I am worried that the User Manual says the charger won't start until the battery has 5v less than the solar panel. As the LiFePo4 battery should keep a useable 12v down to say 20% of capacity, does that mean it won't start to be solar charged until almost flat at 0% ?

Maybe I should stick with a simple PWM charge controller - but how to detect and cut-off the charge at under 5 degrees C ?

I've done loads of internet research with no solid answer to my situation, and would be very grateful for your good advice.
=======
PS> My web research has now lead me to Votronic MPP solar charge controllers, which are looking more promising...

(Also posted on the Victron Community Forum)

Many thanks - James.

 

[funflair]

Stick a voltmeter on the panel connections at the regulator and that will give you a clue, my guess is 18+volts so you would be OK.

A Votronic MPP needs a temperature probe when set to LiFePO4 profile so that should do you as well.

I have found Votronic very good at answering question if you want it straight from the experts.

Martin

 

[Off da Grid]

The guys at Photonic universe are really helpful for advice I bought my Votronic 350 duo mppt from them after asking advice for the best controller for my 255watt panel.

 

[olsgreen]

So, I thought what might suit would be a Victron SmartSolar MPPT 75/10. Add a Victron Smart Battery Sense to show temperature and use the VictronConnect app to set the charge to cut-off at under 5 degrees C - will this set up work OK ?

I've got the 75/15 charge controller, superb bit of kit, it will do what you're asking regarding cut off and tons more. The controller has an inbuilt temp sensor, so I use that instead of the additional bluetooth one, although I'm going to buy the external one you're talking about and fit that for better accuracy. It also has a preset for LiFePo4, however check this against your battery manufacturers profile.

But I am worried that the User Manual says the charger won't start until the battery has 5v less than the solar panel. As the LiFePo4 battery should keep a useable 12v down to say 20% of capacity, does that mean it won't start to be solar charged until almost flat at 0% ?

No, it will charge just fine providing your panel is putting out 5v above the battery. So if your battery is at 12v, your panel will need to put out at lest 17v for the charger to kick in. Large panels will usually put out above well above this, for instance mine puts out 30v+. I think the Votronic require a similar margin to start charging.

 

[autorouter]

I have an old Land Rover Defender 130 camper van which has been happily running a 123W (12v) solar panel

They are referred to as '12V' panels because their voltage range is up to maybe 22V. Since the controllers need to see a panel voltage 5V more than the battery, they are fine for 12V batteries. But no good for 24V batteries, which need 30V or more.

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[James130]

As feedback, in the end I went with Votronic...

1/ MPP 250 Duo solar charger/regulator
Yes, too 'big' for my current 123W solar panel, but will be able to handle another panel I suspect I will be installing in the spring. Also trickle charges the engine starter battery.

2/ LCD Solar Computer S meter display
Gives plenty of useful info, or just a simple % or Ah left.
Needed a full mains charge of battery for the meter to learn what 100% charge level was before it worked OK. Interesting to see the power draw of fridge, lights etc. My fridge (Engel compressor) is 12vdc only and is power hungry, but can still make ice when 40 degrees C ambient.

3/ Temperature Sensor
Needed for LiFePo4 battery to significantly reduce charging when below freezing.

4/ Bluetooth Connector S-BC
Gives loads of info from both the solar charger and battery on your mobile phone or tablet etc.
The free app is only in German, but I've got the hang of it.
Useful for checking the state of things without having to get in the van and look at the meter.
Checking up from the kitchen window became a bit obsessive, but I am recovering, slowly.

It all connected up well and I am pleased with the set up and quality.

Cheers - James.
Land Rover Defender 130 camper, converted by Foley.
Originally an MoD pick-up called a Rapier due to the Surface to Air missile trailer it pulled.
First built 1988, with a full rebuild and the camper conversion done in 2004.
It no longer has the missile launcher.

 

[fat haggis]

Lovely defender did you make it yourself. More pics please.

 

[poppycamper]

It no longer has the missile launcher.

Shame.... could have come in handy
James130... apart from blue tooth gizmo that is exact set up I have which I must say I am delighted with.