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Author Topic: Seeking voltage limiter recommendations  (Read 3303 times)
KD2JIP
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Posts: 28




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« on: July 18, 2018, 10:43:44 AM »

A quirk of my portable power setup with solar charging is that under certain conditions, the charge controller sends solar panel Voc of up to 22V to the load.  This would fry my KX2.  I work around this problem by never connecting the panel and the load to the controller simultaneously. 

I would prefer to float the battery while powering the load from the panel as much as possible. I might be able to achieve this with a different charge controller or battery pack, but I'd prefer to first see if I can find a regulator that will limit the max output voltage.

I tested this adjustable output step up/down switching voltage regulator from Pololu.  It's very small, RF quiet and efficient, but its max output current is only 2A, which doesn't allow my KX2 to transmit at full power.

I also tried this one, which satisfies my power requirements.  But it's extremely noisy--it obliterates strong, clear signals on 20m and 40m.

The advantages of a buck boost converter are that it protects my load from panel Voc and it maintains a voltage that allows my KX2 to operate at full power as the battery discharges (although draining the battery faster).  But I'm not 100% sure that a buck boost converter is necessary--maybe some other simpler component would work.  My essential requirements are:  1) max output voltage limited to around 13.5V;  2) max output current of around 5A; 3) as efficient as possible;  4) as RF-silent as possible;  5) as small and light as possible.

Any recommendations?
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K5LXP
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« Reply #1 on: July 18, 2018, 03:42:42 PM »


A 15V zener rated to dissipate the maximum panel capacity across the panel output is RF quiet and very simple.

Mark K5LXP
Albuquerque, NM
 
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WB6BYU
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Posts: 18396




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« Reply #2 on: July 20, 2018, 08:50:20 PM »

And if you don't want to buy a large zener, use a smaller one and a big transistor together.
Such a combination can draw 20A or more (assuming you have enough heat sinking) to
load the panel down and keep the voltage within range.
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W8JX
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Posts: 13268




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« Reply #3 on: July 21, 2018, 04:04:07 AM »

How about a load bank on solar panel output too to keep it loaded so voltage does not spike high. It can be a few high wattage power resistors of proper value. It could be switched out when not needed and reduce energy needed to be dissipated by a zener.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KD0REQ
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Posts: 2366




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« Reply #4 on: July 21, 2018, 01:51:42 PM »

Get the schematic of an Astron PS off the repeater builder site. Build the part after the filter caps. Done. The voltage max out of the panel is the voltage passed into the control board. Or just put two big-arsed diodes in an Astron cathode common, one anode back to the cap, one anode to the solar bank. Now you have a diode-switched Astron that will take the higher voltage from either source without impressing backflow into either one. Just like a big telco.
« Last Edit: July 21, 2018, 01:56:00 PM by KD0REQ » Logged
WB4SPT
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Posts: 773




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« Reply #5 on: July 22, 2018, 06:33:51 PM »

A quirk of my portable power setup with solar charging is that under certain conditions, the charge controller sends solar panel Voc of up to 22V to the load.  This would fry my KX2.  .

Certain conditions related to RF?  I come across numerous regulator designs, even very popular reference V IC's that are quite sensitive to RF.   But, taming is possible. 
Solve the primary issue, don't chase a bandaid. 
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AA4PB
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Posts: 15022




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« Reply #6 on: July 22, 2018, 07:30:56 PM »

No solar charge controller should ever send 22V to a 12V battery and load. It sounds like either your battery is bad or it is disconnected from the system. A solar panel can put out 22V with no load but the charge controller should limit the voltage to about 14V with the battery connected.
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Bob  AA4PB
Garrisonville, VA
N3QE
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Posts: 5576




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« Reply #7 on: July 23, 2018, 06:30:22 AM »

Normally a solar panel would feed a charge controller which feeds the battery which feeds the radio.

The battery acts as a pretty good 14V regulator.

You might want to rearrange your wiring such that the battery can never be disconnected while the radio is still hooked to the charge controller. I might recommend one set of wires from the battery to the radio, and a different set of wires (with a different plug) from the battery to the charger.

Others swear up and down that a charge controller will never put out 22V. And I agree, it would never do that to a battery. But in my experience if the battery isn't there then all bets are off. That charge controller was designed to charge a battery and not protect a radio.
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W8JX
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« Reply #8 on: July 23, 2018, 07:18:35 PM »

The battery acts as a pretty good 14V regulator.

Only if it is a big battery and panel only makes a few amps or so max.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
AA4PB
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Posts: 15022




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« Reply #9 on: July 23, 2018, 08:11:04 PM »

The battery acts as a pretty good 14V regulator.

Only if it is a big battery and panel only makes a few amps or so max.

If the charge controller is allowing the voltage on a 12V battery to be pulled to 22V then the battery is not going to last very long. It's time for a new charge controller if yours is doing that.
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Bob  AA4PB
Garrisonville, VA
W9IQ
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Posts: 3240




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« Reply #10 on: July 24, 2018, 04:05:50 AM »

If the charge controller is attempting a current regulation phase for battery charging, it would not be unusual to see 22 volts when the battery is not present. The charge controller is attempting to raise the charge current to a predetermined level but with no load, it will reach the maximum of its supply voltage.

- Glenn W9IQ
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- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KJ4HVL
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Posts: 143




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« Reply #11 on: July 31, 2018, 11:24:17 AM »

As others have stated even a small 7AH sla battery will drag down the output voltage, my panel will do 24V OC, but with even a tiny load falls to 15v. That said, I have purchased some of the DROK buck converters on amazon for my power kit (I have mine inline between the panel and the controller with a peak limit of 14.8V). They are a little noisy, so a coil of wire on the output through a ferrite, and shielding the switching module itself is important... However without those protections I've worked wspr from the US to Antarctica and Tasmania, with the only noticeable issue being the pop-pop-pop of the pwm charging circuit from my controller.

The benefit of locating it at the input to the controller, is if your controller fails, you can actually use that module as a CC / CV charge controller in and of itself, and in bright sunlight, you could probably even run a rig directly off the panel (so long as you dial back the power a bit)

https://www.amazon.com/dp/B0744BT79M/?coliid=I2WNLLPKXTEIER&colid=107GIW97E1MA2&psc=0&ref_=lv_ov_lig_dp_it
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KD2JIP
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Posts: 28




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« Reply #12 on: August 18, 2018, 06:56:40 AM »

Certain conditions related to RF? 

No.  By design, the internal BMS board disconnects the battery when charging rate falls to 0.02C.
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W8JX
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Posts: 13268




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« Reply #13 on: August 18, 2018, 07:35:19 AM »

As others have stated even a small 7AH sla battery will drag down the output voltage,

Not that well as regulation will depend on battery charge state and it will shorten its life. If you go battery route, you want a bigger battery.
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Ham since 1969....  Old School 20wpm REAL Extra Class..
KD2JIP
Member

Posts: 28




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« Reply #14 on: August 18, 2018, 07:40:11 AM »

After further consideration, I decided to replace my battery.  I built a higher capacity pack (6.6 Ah as opposed to 4.5 Ah) using a PCM board that doesn't disconnect the battery near end of charge.  The PCM top balances the cells at 14.4V, so, unfortunately, I had to replace my 14.2V charge controller, too.  I went with the same model controller, custom programmed with a CV voltage of 14.4V.

My setup now functions as I had hoped.  The load is now exposed to a maximum of 14.4V, so I can keep the panel and load connected at all times.  This allows the controller to power the load from the panel when possible and from the battery when necessary.

I would still like to put a voltage regulator between the controller and the load, no longer to protect the load, but to keep it powered at >= 13V as long as possible when running on battery.  This would maximize the amount of time I could transmit at full power (the KX2 will transmit at its max of 12W as long as input voltage is >= 13V).  I don't know if a regulator like this is available to buy or feasible to build.  Current draw while transmitting and powering a Raspberry Pi (for digital modes) is between 2.5A and 3A;  I'm not sure if this would require a regulator with constant current...
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