Scope creep on replacing solar charge controller

dlichterman

Explorer
So I think my sunsaver pwm charge controller is acting up - I noticed my 12V deep cycle battery wasn't getting charged under full sun. I am going to start probing wires this afternoon when I get home from work, but I've been thinking about switching to a MPPT controller to get that efficiency bump. I have 2x100W Renogy panels currently wired in parallel. From the specs:
Optimum Operating Voltage (Vmp): 18.9VOpen-Circuit Voltage (Voc): 22.5V
Optimum Operating Current (Imp): 5.29AShort-Circuit Current (Isc): 5.75A

So, if I'm reading this correctly - the maximum voltage these would produce if wired in series would be ~45V, at around 12 amps. Currently they are wired in parallel. With switching to putting them in series I would be able to run a charge controller such as the victron 75/15, right?

It seems that if I go to series, I would be getting more power in the mornings and evenings because I'll be getting up to charging voltage sooner. Seems like a no brainer to switch to MPPT, but at the same time switch to series because they can usually handle the higher voltage.

Any thoughts? Have I read things correctly on the specs of various devices?
 

dlichterman

Explorer
Oh lord, yeah duh its same amps at higher voltage. That's what I get for trying to post during my lunch haha.

But seems like that means the lower rated controllers will be fine if I go series, and heck it'd even work in parallel, though it would be close to the max amps.
 

jonyjoe101

Adventurer
on the victron, they got several versions the cheap one doesnt come with the doongle to adjust bulk voltages, you have to buy extra. But a newer version has a built-in bluetooth. You need to able to adjust the bulk voltage in case you have voltage drop from controller to battery.

Another good mppt is the ecoworthy 20a (its what I been using for 5 years on my 240 watt panel). Its got a built-in lcd screen showing voltage/amps and is programmable from the buttons on the unit. But like victron the newer models are bluetooth with no screen but you can still find the older ones. After 5 years running 24/7, it still going on strong, now I'm using it to charge my 220ah lifepo4, thats why being able to program the bulk voltage is a big plus. I can also charge another lead acid battery from the load out . I paid 105 for mine.

Connected in series 200 watts will get you about 10 amps. With the ecoworthy I only get 12 amps out of my 240 watt panel when doing lead acid on lithium sometimes I see up to 15 amps.
514578
 

dlichterman

Explorer
Well I unplugged the solar panels to check the voltages, and when I plugged them back in, it started working again :/

Some of the newer units that have BT or a remote display are what interest me as the charge controller is buried in the front(back?) of the bed of the truck behind the battery box, up against the wall of the bed, so I can't really check it without crawling back in there.

Also thinking about going in series for less amps since that would in theory mean less loss through the wiring?
 

hour

Observer
I have the victron 75/15 running 2x100w renogy panels but in series. I know I ran them in parallel over a two year period with a few PWM cheapo controllers before I went MPPT. Sadly I don't remember anything about power stats, or observations when I initially switched. If your wiring is adequate as-is I wouldn't make it a deciding factor for switching to series, but I'm super happy to not have any typical hard plastic dog-in-bathtub solar cables anymore. I just use 12 gauge low voltage landscape lighting wire now and didn't stress over making my run as short as possible, which allows me to move my battery box around in the bed of my truck and coil up the excess if needed.

The bluetooth monitoring is a huge selling point. I can lay in bed (at my house and in my camper) and see what's going on with the system. Much satisfaction to be had for a nerd like me.
 

dwh

Tail-End Charlie
In series 45 volts @ 5.29 Amps and in parallel 22.5 volts @ 10.58 Amps
Yes...and no. :)

You're right that he flubbed the math doubling both the voltage and the amperage.

But...it wont be putting out full amperage at Voc. With MPPT at rated Vmp it would be 37.8v, not 45v.
 

dlichterman

Explorer
Yes...and no. :)

You're right that he flubbed the math doubling both the voltage and the amperage.

But...it wont be putting out full amperage at Voc. With MPPT at rated Vmp it would be 37.8v, not 45v.
Right - I was just using open circuit as the max that it could possibly see as a comparison to the max rating. I'm still not sure what to do - it seems like maybe I need to be in parallel sometimes and series sometimes - which is easy enough to change the wiring up there. But the 100/20 Victron has better heat sinks than the 75/15 and I'm in socal....it gets warm sometimes.
 

dreadlocks

Well-known member
Controllers should be sized for total VOC and then some.. not VMP, those ratings are at lab temps of like 78F IIRC.. as temps drop, those voltages will go up.. If you get a 75V controller and hook it up to 70V of panels, you could go for a good while til that one bad day in the winter when conditions are right to feed it 80V and toast your controller out of nowhere.

Series can let you oversize your solar which means a smaller, cheaper controller with excess panels.. a 15A controller can take 15A in and 15A out, putting em up in a series as long as your within the voltage rating lets you put more solar on than you need which increases output in shady conditions.
 

luthj

Adventurer
Many MPPT controllers are output limited (in amps). Input power is always limited by output (charging) power. Assuming you are within the limits of the controllers input voltage, going with a larger array than the max output watts/amps is fine (generally speaking). The controller simply won't be able to use the peak power the panels may produce in ideal conditions. Those are pretty rare for flat mounted panels anyways.
 

IdaSHO

IDACAMPER
going with a larger array than the max output watts/amps is fine (generally speaking).
Actually, thats ideal! As mentioned, ideal conditions are rare.
So running a larger array is never a bad thing. Just a bit more weight.

And Ive yet to find a controller that has trouble with excess current.
They are designed to run up to a their max current rating, then shed the rest.

No harm done.

Just do the controller a favor and not run past the rated voltage.
THEN you might let the smoke out

Connected in series 200 watts will get you about 10 amps. With the ecoworthy I only get 12 amps out of my 240 watt panel when doing lead acid on lithium sometimes I see up to 15 amps.
View attachment 514578

You've got problems if you are only seeing 12A from a 240W panel.
I routinely see 17+ out of my 200 watt array using the same controller.

And yes, the ecoworthy is a decent controller. Mine has been in service for 4+ years now.
 
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