I recently acquired several pieces of road construction type equipment. Each unit was equipted with either five 90 watt solar pannels, or six 75 watt panels (450 watts either way). The charge controller on all of the units is the same model, but seemingly very basic. See attached pictures. I don't believe the controllers are working properly. In full sun, with my multimeter on the terminals coming from the pannels I am showing about 18 volts, as expected. However, I am showing the exact same voltage on the terminals going to the battery compartment. I would have expected to see output aroun 13 or 14 volts. I plan on buying a more modern controler at some point, but was hoping to get it working first with the existing parts, but now I'm uncertain. If anyone has any thoughts on this particular 15 year old controller, or recommendations for a modern controller, I'd appreciate it. Keep in mind I plan on starting with 3 of these panels installed, but I think I want a controller with the ability to handle 5 or six of these panels.

I can't say about the existing CC but with a 400+ watt capacity go with a MPPT.If you do series strings match the current ratings, if parallel match the voltage +/- 10% on the voltage.

We have a Morningstar MPPT controller and from first hand experience one of the better companies.

That charge controller would more than likely be a PWM and the output voltage would be the same as the voltage going into it.

Looks like controller is fried.Those panels are called "nominal 12V". 5*12V panels wired in series with total 450W requires 45A MPPT controller, cost around $400. There is usually VERY little reason to use multiple 12V panels for total 450W array. 2*250W will be easier to install and easier to wire, not to mention possible loss of performance in old panels.

All I could afford wrote:In full sun, with my multimeter on the terminals coming from the pannels I am showing about 18 volts, as expected. However, I am showing the exact same voltage on the terminals going to the battery compartment.Is this attached to a battery?attach to a battery and remeasure and re-post results.New, those panels should measure 21v not connected to a battery, relatively cool, 25C.connected to a battery while charging, you should measure batt V.

Solar controller selection for existing pannels

24 Replies

red31
Explorer
Mar 02, 2016
Salvo wrote:
That's a great graph. I don't understand why panel voltage is lower when in float. Is that really float?

Actually the battery voltage plot doesn't look right. When charging, it should be ramping up. Outside of a couple of bumps, it's flat. Why is there a bump up around 10:00?

very shaded/low light. low charge current, it was ramping up just slowly, I never figured out how to capture the data and make my own graph with expanded scale. I hooked the controller to a PC and used view star's software and screen capture to get the graph.
MrWizard
Moderator
Mar 01, 2016
That increase is when the sun gets high enough to increase output from the panels, the time of morning that happens will depend on your location/ latitude
Salvo
Explorer
Mar 01, 2016
That's a great graph. I don't understand why panel voltage is lower when in float. Is that really float?

Actually the battery voltage plot doesn't look right. When charging, it should be ramping up. Outside of a couple of bumps, it's flat. Why is there a bump up around 10:00?
red31
Explorer
Mar 01, 2016
Here is a graph of my panel/battery voltage
The batt and panel have the same voltage until the 14.6v batt set pt is reached.
At that time, panel V seems to rise, this is PWM, connecting and disconnecting the panel to limit power to the battery to maintain the set pt V. Connected, the panel voltage = batt V, disconnected, the panel voltage is Voc, the controller's V meter reads this as an average and as more time is spent disconnected, the panel V rises. The lower panel V after it peeks ~20V is due to low light conditions, the controller goes to float (13.4v) ~noon.

Data captured from a View Star 1024BN

Here's my concept of 50% PWM duty cycle, the controller displays 'PV 17.9v, 2A', 'Batt 14.8v, 2A'
All_I_could_aff
Explorer
Mar 01, 2016
Thanks everyone, I have panels set up In my yard and 2 hungry batteries standing by for this weekends testing.
Boon_Docker
Explorer III
Mar 01, 2016
OP - If you are getting 18v from the panels and 18v output from the controller then your controller is more than likely a PWM controller and it may be functional. Hook up the panels to the controller and controller to a battery and see if it will charge the battery and then shut down when the battery is fully charged.
Almot
Explorer III
Mar 01, 2016
Mr Wiz - right now I have a fainter yet idea of what the OP wanted to know :)... Though it looked a little clearer at the beginning.

OP - if you only have room for one or two panels, then 20A controller is plenty. If your existing 30A works, - keep it. Or get some better 20A PWM model.
Yes, 2*90W panels with small PWM controller and 12V battery should be wired in parallel.
Ed_Gee
Explorer II
Feb 29, 2016
red31 wrote:
Ed_Gee wrote:
red31 wrote:
All I could afford wrote:

In full sun, with my multimeter on the terminals coming from the pannels I am showing about 18 volts, as expected. However, I am showing the exact same voltage on the terminals going to the battery compartment.

Is this attached to a battery?

attach to a battery and remeasure and re-post results.

New, those panels should measure 21v not connected to a battery, relatively cool, 25C.
connected to a battery while charging, you should measure batt V.

Red31 raises a good point. In all probability that controller needs to be attached to a battery before you can assess whether or not it is working. However, his comment that open circuit panels should show 21VDC is questionable ... that depends quite a bit on the design of the panel ... my new monocrystaline panels show 18VDC open circuit, as yours do so in all probability your panels are OK.

the sticker on the back of the panel shows 21.6 Voc, rated 17v (Vmp).
here's the new panel specs in a different format
http://www.solardirect.com/PDF/SolarElectric/sr90p1n.pdf

Red31 -- I apologize for my misinformation. I was thinking of maximum power point rather than open circuit voltage. My panels also measure about 22 volts when nothing is connected to them - Grape Solar model GS-S-160 monocrystaline.
red31
Explorer
Feb 29, 2016
All I could afford wrote:

but was hoping to get it working first with the existing parts,
MrWizard
Moderator
Feb 29, 2016
In OP, I don't remember anything about using these on the RV
The panels are on the construction equipment
And the question was what do I need to get it working

I answered that question
Almot answered what you really wanted to know
Maybe he's becoming a mind reader