CTEK 250S Poor solar performance

vtsoundman

OverAnalyzer
After spending 8 days on a remote mountain top relying on the CTEK 250s to charge batteries from solar, I can wholeheartedly say DO NOT buy their 250S product if you need decent solar performance. Charging from the alternator, it does fine/as expected.

The charge times are insanely long as it goes into MPPT search mode constantly. With 150W of matched panels, the constant sweeping resulted in 40% loss of harvest energy (was using a tracking meter). This is the second CTEK 250s I have seen constantly sweep the solar input.

It never charged my main (starter) battery as claimed it is as it never reached float on my 100ah aux battery.

Per the Victron BMV 712, I never exceeded 95% SOC with the CTEK ... And the aH counter supported that. The 712 had been in use for a while and the SOC meter and aH counter appeared accurate when verified with external metering. I also never reached float.

To make sure I wasn't Looney tunes, I swapped in a Victron 75/15 for two days and it charged my aux battery in ~5 hours while supplying the same loads and same panel wiring (all parallel) was used. On the second day, the day loads were heavier as I charged 3 handheld ham radios, but the time to float was about the same.

After my aux battery dropped to float, I jumpered my 100ah main start battery to bring it back up to snuff as it powers a few of the outside scene lights and charges my handheld GPS and phone. Topped it off in about 3-4hrs.

Night loads consisted of two ham radios, small battery recharging, small inverter, circulation fan, and dometic fridge. Day loads were ham radios and fridge.

I routinely pulled ~25-30ah overnight. Conditions were the same each day : clear and cool, at 6500ft...so great insolation levels.

I'll call ctek and see if they have any answers about this or have updated the firmware on the 250s versions...my experience with their support in the past was less than stellar
 

john61ct

Adventurer
I've been saying this for a long time.

I think the intention is, it's freebie add-on good for keeping a batt full when not being used.

For more serious needs a quality dedicated SC is called for.

I also prefer a DC-DC with user customizable setpoints like Sterling's BB line.
 

brianjwilson

Some sort of lost...
Maybe you’re short on solar or have an issue somewhere else.

I’m using a d250s (alternator/starter batt not even connected) with a 255a/hr agm and 300 watts of solar. Isotemp fridge runs all the time, furnace lots of nights, led lights, I always sleep with a fan blowing on me, charging multiple devices and listening to music through a 12v usb speaker. Rarely see voltage below 12.7 in the morning, absorbing at 14.8v whenever I look at it mid day unless it’s dumping rain. I’m on the Oregon coast (fog and clouds) 55% of the time.

Right now my ctek is going right to the battery through a circuit breaker. I do have a shunt and battery monitor but I don’t have that stuff hooked up yet. Wondering if you’ve got something else interfering, too small capacity or a faulty charger or battery.
 

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john61ct

Adventurer
What VoC are your panels?

For all posters adding data points, very relevant here.

Same wattage but higher volts,

the MPPT functionality of a (e.g.) $110 75/15 will give a much higher efficiency conversion, even 20% or more, especially when you get up above 30V, up to a max around 65V.

Get too far below 20V, might be better off just sticking with the CTEK, which is limited to 23V input from panels.
 

vtsoundman

OverAnalyzer
Maybe you’re short on solar or have an issue somewhere else.

I’m using a d250s (alternator/starter batt not even connected) with a 255a/hr agm and 300 watts of solar. Isotemp fridge runs all the time, furnace lots of nights, led lights, I always sleep with a fan blowing on me, charging multiple devices and listening to music through a 12v usb speaker. Rarely see voltage below 12.7 in the morning, absorbing at 14.8v whenever I look at it mid day unless it’s dumping rain. I’m on the Oregon coast (fog and clouds) 55% of the time.

Right now my ctek is going right to the battery through a circuit breaker. I do have a shunt and battery monitor but I don’t have that stuff hooked up yet. Wondering if you’ve got something else interfering, too small capacity or a faulty charger or battery.
You're barely touching that battery...12.7V after an evening of usage suggests that it won't take long to recharge your batt. However, all agms are not the same - so hard to say without looking at the actual curve. My guess is your pulling maybe 20aH-30aH out at most and are running 2x the solar...so even the marginal performing CTEK will be fine.

I'm pulling 20- 30aH out per night, not including the loads during the day on a 100aH battery. Sometimes more, but avg is 20-30ah. My resting OCV is right around 12.4-12.5V which tracks with discharge amount, theSoC remaining, and the battery temp.

Both CTEK 250s I have owned have always cycled the solar current up and down a ridiculous amount...this one is about 2 yrs old. The other is closer to 5 yrs(?) old.

3 x 50W modules have a Voc of 21.6V, MPPT of 17.6V and an indivual Isc of 3.05A at STC. All were wired in parallel each with their own #12awg on a 30' run to a short 5' long 3 way wiring harness combiner into the CTEK via #10.

Appropriate voltages and currents were measured given the module temps. Modules' angles (both tilt and azimuth) were optimized about 5 times a day around the same time. Full sun, no obstructions or partial shading. I was also at ~6800ft...150W nameplate is more than plenty of solar for what I was doing, my battery size, and the duration I had to charge.

The ctek 250s has a paltry max solar voltage of 22V (nearly worthless for anything but the smallest systems - like 3 of my 50W modules) - which means the panels MPPT will be pretty close to absoprtion leaving the controller little regulation headroom. My Victron indicated Vmppt was 16.6 volts or so at it's lowest (hottest module temp) with a current of ~8.2-8.5A which tracks with module temps. Peak avg solar power was a stout 135W with it averaging around 120W!! Modules are fastened to a PVC structure allowing full air circulation to reduce temp coef impact.

Battery is a 100aH sealed generic agm, deep cycle. Impedance and DoD testing suggest the battery is at 95% capacity after 3 years, damn respectable...but I also take care of the battery. Testing occurs once every 4-6 months. The battery has a max charge current limitation of 30a, so the 20A limit of the CTEK lines up nicely.

If I wasn't stationary for so long (more than a couple of days), the poor CTEK solar performance would not/does not matter.

As I had posted a few times long ago, the Victron returned the system to fully charged about 20% faster than the 250S - a disparity I could have lived with - but this go around, the CTEK couldn't even top up the battery it was so bad.

Recall that I also said : a Victron 75/15 (an MPPT controller) was used for two days with the same wiring and loads and resulted in much better performance. On my last full stationary day, I paralleled my aux battery and starter 100aH battery I estimated the starter battery was down about 30aH... The Victron charged both of them both of them without issue.

As an aside - curious about how much current my 165A Jeep alternator could produce and how much current a 50% depleted battery would accept from the alternator, so I decided a test & measure it.

I left my 2 x 100W high beams, my 2 x 100W hellas, other random lights charged my laptop and ran my small lithium charger via an inverter for a total pull averging about 50A over the course of an hour - so I pulled about 50aH at a bit less than 0.5C.

The Jeep fired right up. Peak current during start was 265A. At 1000RPM, the alternator was pushing 75A into the battery. At 3000RPM, it hit 115A. I kicked on the CTEK for another 25A plus my fridge load. The engine/jeep consumes about 22-27A on it's own. Cooling fan on high draws about 30A. The Jeep alternator voltage, never droped below 13.9V for more than a second or two and usually maintained 14.4- 14.5V.

I then kicked on my dual viar 88P compressors (one pulls ~14A, the other ~17A) for an additional load of ~31-34A. Alternator never broke a sweat - voltage dropped a bit to 13.8 before the system recovered and pushed it back to 14.2V. Battery acceptance dropped to about 60A at this point. Total alternator load was ~115A at 1000rpm.

All current values were average, and not peak, except at indicated. Jeep is a 2007 wrangler Rubicon with orignal factory 165A alternator.

Edit: typo fixes.
 
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vtsoundman

OverAnalyzer
What VoC are your panels?

For all posters adding data points, very relevant here.

Same wattage but higher volts,

the MPPT functionality of a (e.g.) $110 75/15 will give a much higher efficiency conversion, even 20% or more, especially when you get up above 30V, up to a max around 65V.

Get too far below 20V, might be better off just sticking with the CTEK, which is limited to 23V input from panels.
MPPT is always much more effective, regardless of the Voc - a competent charge controller only needs about 2V to maintain proper regualtion and control bandwidth at these power and voltage levels. For startup, a competent controller will need ~4V between solar and battery voltage.

The issue is the CTEK algorithm is crap - either the battery charger is doing some gimmicky crap or, more likely, CTEK is doing some rudimentary MPPT search algorithm with an improper timing structure such that it sweeps (relaases) panel voltage far too frequently. My guess is the solar algorithm is poorly tuned since I never see this much charge current variability while the CTEK is current from the alternator...in fact I see very little.
 

john61ct

Adventurer
A wider voltage range between Voc and output gives the MPPT more leeway to optimize.

So with 19Voc panels, the Victron advantage will be far less than with any say standard 24V nominal ones, usually ~40V.
 

brianjwilson

Some sort of lost...
Did you talk to ctek yet?

Ironically mine has been working great until the last week. Haha. Only the fridge running. Parked inside half of the days. But it’s been outside in the sun, now light overcast, and I came back after a few days to find the battery at 12.3v. Watching the lights it appears it is turning off solar input every couple minutes (haven’t timed yet) and coming back on. It did not previously do this when I’ve watched it.
 

vtsoundman

OverAnalyzer
Did you talk to ctek yet?

Ironically mine has been working great until the last week. Haha. Only the fridge running. Parked inside half of the days. But it’s been outside in the sun, now light overcast, and I came back after a few days to find the battery at 12.3v. Watching the lights it appears it is turning off solar input every couple minutes (haven’t timed yet) and coming back on. It did not previously do this when I’ve watched it.
I did speak to them about their solar performance...and each time got no where. Farthest I could get was the tech support person telling me to unplug the unit...and if the solar comes on right away, the unit is doing what it is supposed to do. Given that both of CTEK 250s units are doing this, I'd say it is a design feature. I'll ping them when I get back from my next camping trip...but soon I will be replacing both of them with KISAE DMT1230 or DMT1250 - and I will post a review of those units soon. Very pleased with their performance and it is within a few percent of Victron solar performance....AND tehy are ADJUSTABLE. Why is that Redarc, Sterling, and others have such poor custom tuning? Anyhow...

Let me know if you get anywhere.
 

john61ct

Adventurer
True for redarc, but I know every Victron I've seen are very customizable.

And what Sterling unit do you mean?
 

vtsoundman

OverAnalyzer
True for redarc, but I know every Victron I've seen are very customizable.

And what Sterling unit do you mean?
Victron doesn't have a B2DC charger. All of the Sterling units, from what I can tell, are programmed via an archaic interface and you must follow their canned schemes.
 

coolfeet

Mark Keeler
I have the CTEK D250 connected to my alternator only. It's a beast when connected to the alternator. Keeps everything fully charged.

The upper limit of 22-23 volts is not enough for my 2 160 Watt solar panels connected in series. I tried using the panels connected in parallel with the CTEK and the result was okay, but not great. It seemed like I was throwing out a lot free solar power.

I am buying either the Renogy or PowMR MPPT solar charge controller to use while dry camping.
 

john61ct

Adventurer
I was responding to this.
Very pleased with their performance and it is within a few percent of Victron solar performance....AND tehy are ADJUSTABLE. Why is that Redarc, Sterling, and others have such poor custom tuning?
And Sterling BB series is the only adjustable DCDC I've come across so far. Not just canned choices, user tunes custom setpoints, e.g. 13.8V for 4S LFP

Only go to 80A I believe ATM, up to 240A coming.

But easily stacked.
 

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vtsoundman

OverAnalyzer
I have the CTEK D250 connected to my alternator only. It's a beast when connected to the alternator. Keeps everything fully charged.

The upper limit of 22-23 volts is not enough for my 2 160 Watt solar panels connected in series. I tried using the panels connected in parallel with the CTEK and the result was okay, but not great. It seemed like I was throwing out a lot free solar power.

I am buying either the Renogy or PowMR MPPT solar charge controller to use while dry camping.
Partially shaded arrays (one in full sun, one in shade) perform better when connected in parallel.

My CTEK testing revealed terrible solar performance when compared to Kisae or Victron without changing the wiring configuration. Regardless, with 320W or solar, you're getting close to the upper edge of the CTEKs capabilities.

If you have the room for the voltage, try series and parallel, shaded or otherwise...the presence of bypass diodes in the module will impact the total yield of a series connected array.

For dedicated solar unit, I'd suggest a Victron with Bluetooth...it's allows you to quickly see when you have to move/re-tilt your array for max production or deal with trees. When I am working/staying at base camp for the day, I'll set an alarm on my phone every 2.5 hrs to re-aim my portable array forax production.
 
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