Charge Controller Operating Envelope?

[NatersXJ6]

I’ve decided to take the solar plunge. Like so many projects, I have grand plans that will probably be limited by a series of cost and construction ion considerations long before I see power to a battery, but I’m still in theory (fantasy) land, so I have a theory question:

Is it generally better to run an moot charge controller in the low to mid-range of its operating envelope (with respect to current) than at the top end? It seems to me that this would result in lower heat and potentially longer life, sort of analogous to lightly loading an engine.

So specifically, if I expect to have a max current of 27 Amps, and my rating choices are 30 or 50, should I pick 50? Cost is negligible between them, although installation size might be an issue.

I think I’m really looking for which one will run cooler and more reliably?

Thank you for sharing your experiences and knowledge.

 

[dreadlocks]

if you expect to have a max current of 27 amps, just get the 30.. cuz IRL your probably rarely gonna see more than 20amps.. both would be fine, they dont generate much heat waste at all so your concern is largely moot.. Ive hooked over 50A of panels to a 30A controller, it did just fine maxing out the controller, nothing I was worried about.

unless you want more capacity for possible future expansion, but if your built out and never gonna fit another panel on the thing.. then no reason to oversize it really.

 

[john61ct]

Depends on the specific SC.

Victron MPPT for example, is very important to stay well below the max **voltage** rating vs panel Voc.

But on power/current, they give a fair bit of headroom.

So with their 75/15 model, the total panel rating should be well below 70Voc

but going past a **peak** power input of say 240W will do no harm, likely even 300W for a short time.

Even though it will never **output** much more than 220W @12V (15A charging at 14.8V), such "overpanelling" will greatly improve the daily **average** output available per SC.

 

[dreadlocks]

75/15 lists 220W as nominal, you could do 300w indefinitely and its not an issue.. its limit is 15A, once output hits 15A its going to throttle back input.. and since input is a higher voltage, it of course has to be less than 15A.. so its never going to exceed its capabilities as far as current is concerned.. just keep voltage within spec, plus a bit of wiggle room.

In my case the 50A of panels was theoretical output, 100/30 hit 29.9A output and held it solid, since it was ~70V panel, input would be less than 10A at full 650W, well below the controllers output.. manual says . nominal for mine is 440W, and it does just fine w/650W.. and still bring overdriven that much, only hit max output for limited time every day... not like it was sitting at 30A from dawn til dusk, only around noon.

YMMV with various controllers, this is whats found in the Victron Spec sheets:

1a) If more PV power is connected, the controller will limit input power.

 

[john61ct]

Note that the relevant current rating is not the input, there use Watts.

The **bank'****** nominal voltage combined with the **output** current limitation (e.g. 15A) is what determines the maximum Watts output.

That's why a 24V setup gets twice the power out of each SC.

 

[jonyjoe101]

on my ecoworthy 20amp mppt (240 watt solar panel) I rarely see more then 12 amps but the controller gets very hot. I've had a small 80mm cooling fan pointed at it during the day for years to keep it cool. 6 years later still runs hot when running but still works excellent. Its no big deal to put a small fan pointing on the controller, it might or might not make it last longer, but definitely won't hurt it.

 

[john61ct]

The Victrons are fine without a fan, designed to keep cool enough passively, long as you mount according to the directions.

They do cut output if things get too hot, from something silly like mounted in an engine compartment