Charge Controller Amperage...

[06RKguy]

I have a cargo trailer camper conversion, and want to install solar on it. I have bought a 12 volt 100 AH LiFepo4 battery to start, and the manufacturor recommends it be charged at 20 amps. I will be mounting a couple of 100 watt panels on the roof of the camper, but my question is which charge controller would be best for the battery? I have seen kits thta come with 20 amp and 40 amp controllers. Do I have to use a controller that advertises 20 amps?

 

[SamDeleted]

I have a cargo trailer camper conversion, and want to install solar on it. I have bought a 12 volt 100 AH LiFepo4 battery to start, and the manufacturor recommends it be charged at 20 amps. I will be mounting a couple of 100 watt panels on the roof of the camper, but my question is which charge controller would be best for the battery? I have seen kits thta come with 20 amp and 40 amp controllers. Do I have to use a controller that advertises 20 amps?

Its not a big deal, but yea get a 20amp controller


200w ÷ 12v = 16.6amps
300w ÷ 12v = 25amps


Mmm... you could do with 3 x 100w panels if possible to get over that 20 amps mark , but really I don't think charge rate is particularly critical for LiFePo4 anyway, ? 2x100w should be adequate



What we do need to know please is some specs from the solar panels (VOC & VMP) and your MPPTs controllers 'max solar input voltage'

 

[06RKguy]

Its not a big deal, but yea get a 20amp controller


200w ÷ 12v = 16.6amps
300w ÷ 12v = 25amps


Mmm... you could do with 3 x 100w panels if possible to get over that 20 amps mark , but really I don't think charge rate is particularly critical for LiFePo4 anyway, ? 2x100w should be adequate



What we do need to know please is some specs from the solar panels (VOC & VMP) and your MPPTs controllers 'max solar input voltag

 

[06RKguy]

Haven[t bought the panels or controller yet.

 

[mikefitz]

recommends it be charged at 20 amps

Won't matter what charge current you use as long as its below the maximum recomended and delivers enough amp hours for your application. The available charging Ah should be enough to fully charge the battery regularly .
Two 100 watt panels will not deliver maximum power all day, the absolute maxinum at a nominal lithium charge voltage of 13.5 will be 15 amps. You may get the equivalent of 6 ideal sun hours, thus 90 amp hours per day maximum.
The controler for 200 watts of solar needs to be rated at 15 amps or 20 amps and to be a MPPT type. Recomended is Victron Smart,

https://www.amazon.com/Victron-SmartSolar-MPPT-Controller-Bluetooth/dp/B075NPQHQK/ref=sr_1_2?crid=3MA39UQEU45C2&keywords=Victron%2B100%2B20&qid=1701006510&sprefix=victron%2B100%2B20%2Caps%2C225&sr=8-2&th=1

If at some stage you wish to add more panels select a higher power controller.

 

[grizzzman]

I suggest that you plan for the future. As an example ( and this will very likely happen ) you add yet another battery? Just food for thought.

 

[Steve_S]

I just gotta chuck another hing into this... Typically a 100AH battery should be able to take 0.5C Charge or 50A MAX. Why the company suggests 0.2C (20A) is a bit of a flag... that would mean cracking it open to see what they did... Most likely they used 50AH cells set in parallel internally, as they only take 25A charge.

Given the above, I would suggest that you get a solar controller capable of 50A charge rate, because on the rare & odd days it may actually deliver that (this is on a trailer so not optimal by any means). That would also give you some elbow room to use better panels. I would suggest strongly that you look at controllers which can be paired together, such as Victron for example (better now that the prices have dropped significantly) there are others but not generally any of the "Value Grade" models.

Remember that a Solar Controller regardless of output amp capability, it can only deliver what teh solar panels can provide. If the solar panels can only generate 50% of their spec, then that's all the SCC has to work with and will likely only deliver that percentage. IE my Solar can provide 172A to charge (on the perfect day) but on a cloudy day I'm lucky to get 1/2 that or lower even...

 

[06RKguy]

I suggest that you plan for the future. As an example ( and this will very likely happen ) you add yet another battery? Just food for thought.

Yea At some point I want to add another battery and another 200 watts of solar panels, but I got to start somewhere.