I recently acquired the 45W kit using my pile o' coupons.  The documentation is thin, and operation of the charge controller left me with many questions.  I couldn't find a schematic on the web, so I tore into the box and chased it out.  The PDF schematic is attached, and is also available on Rapidshare. Disclaimer - some of the reference designators weren't visible, and I probably borked more than one component value.  The general topology should be correct, and the drawing provides some decent insight into what the box does.


The circuit board is one of the "new" ones, acquired in December of 2010.  The circuit board has a label: TPS-545-4A-02.


Q: Does this thing charge when the power switch is in the "off" position?

A: No.  The power switch enables the load outputs, the low-voltage regulators, as well as the charger circuit. If you were to disconnect the small switch wires from the K2 connector and short the two K2 terminals together, the charger would be enabled regardless of the power switch state.


Q: Is the charger temperature compensated?

A: No.  The charger measures against a TL431 voltage reference.  When the battery voltage drops below a threshold, the solar panel is connected.  When the battery voltage rises above the threshold, the solar panel is disconnected.  There is hysteresis in the control loop.  I did not measure the threshold voltages.  Other than the TL431's variability with temperature, the voltage threshold is fixed.


Q: Are the low-voltage outputs regulated?

A: Yes, sort of.  The 9V output has a dedicated switching regulator.   The regulator is rated for 1.5A, but I don't know if the inductor and capacitor can support that much load.  The 6V, USB, and 3V outputs are tethered together on a single regulator output.  Diodes are used to drop the voltage from the 6V output.  That's where the "sort of" comes in.  12V is connected to the battery without regulation.


Q: How is power managed, if at all?

A: If the power switch is on, and the battery voltage is above the threshold for the U1B comparator (which I didn't measure either,) a MOSFET switch connects the "load" ground to the "signal" ground, enabling the 12V load outputs and turning on the low-voltage regulators.  The regulators run all the time, regardless of the presence of solar power.  The LED voltmeter display is run from the "signal" side of the circuit, and will be powered even if the battery voltage is too low to run the loads.  If you leave the LED display on, it will drain the battery.  In teh provided schematic, the three-line ground symbol represents the switched "load" ground, while the triangle-shaped ground represents the always-present "signal" ground.


Q: Is the charger optimized for ... anything?

A: It's optimized for cost.  It does not current-regulate, PWM, MPPT, etc.  If the battery voltage is below the "full" threshold, the optocoupler will be disabled, allowing the Q1 MOSFET to connect the solar array's (-) terminal to the signal ground domain.  The solar panels are connected directly to the battery through a blocking diode.

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Nice work. Have to compare my older controllers to this diagram. Thanks.

This is EXCELLENT! Why Chicago Electric doesn't include this info with the 45W kit on a regular basis escapes me....

Those of us with board level understanding can now see the entire picture, quite literally....

Thank you,  migrainman!

Bill K  (K2YI)

Hi migraineman,

Excellent job!  I wish to point out an error for D1 and D2 on the schematic.  The symbols are for Zener Diodes and should be for regular diodes.  They are 3-amp, 60-volt Schottky diodes.  I only point this out for clarity; not criticism.

F2 is an UF400 PTC device, also known as a resettable fuse, made by Tyco/Raychem, and is rated at 4-amps at 30 volts.


These three items are why the HF Controller cannot take more than 4 amps of solar current.  Starting with the Solar Panel (plus) on the left of the schematic, the solar current goes through pin 1 (positive solar terminal) at the back of the controller, continues through the parallel schottky diodes (D1 and D2) and F2 (UF400), then through pin 1 of an internal connector to Pin 1 (positive battery) output to the battery.


That UF400 resettable fuse is guaranteed to hold at 4 amps.  After 4 amps the UF400 heats up and go into a high resistance state and stays there until it cools. It does NOT "blow" as a normal fuse would.   The only way for it to cool is to reduce the current going through it, either by shutting off front rocker panel or by unhooking the solar panels.  Shadows on the solar panels may also reduce enough current to cool the UF400.  Once it cools it allows up to 4 amps to flow again.  A snap-action kind of deal.


Anyone with their controller opened will see those two diodes at the upper left corner of the PC board (LED display pointed at your belly) and the little square mustard-colored PTC Fuse southeast of the diodes.


Thank you for your time, effort, and sharing this information.


Hillbilly Gene






I am wrong about the Schottky Diode symbol for D1 and D2.  You are correct.  Brain bubble went thru.

Hillbilly Gene

Could one not substitute a UF600, RUEF600, in place of the UF400, conceivably bringing the hold threshold state to 6 amps as opposed to 4 amps? Thereby allowing two solar kits on the one HF controller?

Bill K,

I thought of that myself and decided against it.  The UF400 is guaranteed to not trip at 4 amps, but is guaranteed to trip at 8 amps (at 20 degrees Celsius).  Tripping is apparently dependent on its internal temperature.  The UF600 holds at 6 amps, and trip is guaranteed at 12 Amps at 20 degrees Celsius (68 Fahrenheit).  I don't know what happens between the guaranteed hold and trip specifications, but I believe only time to heat is involved.

Running the two parallel Schottky 3-amp diodes at a consistent 6 amps is not advised, nor is running more current over the PC board copper traces.

I think building a small perfboard with heavier diodes and a proper DC breaker or fuse might give the HF controller a higher current rating.  Q1 (IRFB3806), in the negative line, turns off the solar charging current when the battery is fully charged and has a maximum current rating of 43 amps.  My HF Controller has an IRFZ44n for Q1.

One would also have to isolate the heavier charging currents from the PC board, but as a general concept I believe the HF controller could be upgraded to handle more than 3 panels.  If you want your HF controller to possibly take one for the team, go ahead and substitute the UF600.

Have fun.

Hillbilly Gene


Well, Gene, I won't be experimenting, as my fully supplied elctronics bench has turned into a chest of draws since my girlfriend moved in (bench in storage, chest in)....but she can't stop my mind from experimenting...

My comment about the UF600 was only an initial thought, as I am aware (by many "POOFS!" in my time) that beefing up some of the corresponding components would be necessary...and being I have 2 of the HF controllers, I would give one up for the team, I just don't feel comfortable doing so on the coffee table....

Maybe some young experimenter here on the forum will go ahead with our theory(s), and make better this HF controller....

Does anyone know what size F1 PTC Fuse is?  It is the only component that is not identified other than F1.  I fried F1 last weekend some how.  I was using a 65W panel made by another manufacturer but I have used them together for about 9 months.

Thanks for all the info.  New here.  I saw a post that this is a "new board"  purchased in dec 2010.  I have a unit from 2009.  When did they change the board.  My information was that the unit which comes with these did not have a blocking diode to prevent battery drain at night.  Is this part of the newer set up?

Changed SR320's to 6 amp sckotties...Change fuse to 10 amps..

Transistor no need to worry If there Either the IFB3208 or IRFZZ44 they handle over 40 amps switching.

This will give ya some head room for you controllers. Yeah it sounds redundant.

But it works. Did a mod on mine. Hooked it up ...Worked just fine.

Mainly what limits these controllers are the Fuses and Diodes. Everything else is up to Snuff.


You guys clearly have the details worked out.  I don't have enough EE background to dissect the schematics and parts, but I have an application question.


I would like to use the 6-volt output to keep an SLA battery charged.


1) What kind of amperage draw can I get from the 6-volt output?


2) Do I need the 12-volt deep cycle battery to get current out of the 6-volt output when I have sun on the panels?


3) If I do decide to use a 12-volt battery, I presume I would get current out of the 6-volt output all the time.  Is this correct?


6) Does the 6-volt circuit have the same over/under voltage protection as the 12-volt charging circuit?


If not, would I be better off using a 12-volt deep cycle battery and a power inverter followed by a 6-volt smart charger?


Thanks in advance,



Hi Jack,

First, you cannot use the 6-volt output to charge a 6-volt battery, which needs more than 6 volts to charge.

1. )  The total HF controller front panel output current draw is 4 amps.  The 6-volt output is fused for 1.1 amps (Polyswitch XF110 resettable fuse, F5 on schematic.)

2. )  The HF controller outputs will not work without a 12-volt battery attached to it, day or night.  So, yes, you need a 12-volt battery.

3. )  Yes, as long as the 12-volt battery is over 11 volts.

4 & 5. )  ?

6. )  The 12-volt charging circuit will stop amps flowing from the solar panels to the battery when the battery voltage reaches 14.5 volts.  The controller portion of the HF charge controller will shut off all front panel outputs when the battery voltage drops below 11 volts.  (Page 8 of HF kit 90599 manual)

Yes, using a 6-volt smart charger is the better plan.

I don't have an EE background either.  My highest educational diploma was high school.


Hillbilly Gene


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