is MPPT better then pwm or direct connect? Ctek d250s duel

Submitted: Tuesday, Jan 11, 2011 at 20:56

ThreadID: 83605 Views:9337 Replies:4 FollowUps:1

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sup8pdct

I have had the ctek d250s duel for a month now and first use in anger was a trip to frazer island for Christmas. I must say that I am disappointed by the MPPT side of the device.
When running the ctek with solar and full sun, the ctek would draw about 8 amps, add in the amp boost of at best 25%, = 10A in to the Battery. Direct connect the solar to the battery, close to 12A was going in. I would have thought that MPPT would have done better. The battery was running 2 fridges 4 half the day and all night so the battery was nowhere near fully charged.
The battery boost function does as claimed. When charging from both alternator and solar at same time, the ctek appears to direct connect the solar to the alternator (with suitable diode type isolation) which is boosted etc. This was surprising as it appears the CTek has only one current/volt boost circuit. For the trip, I was far better off direct connecting the solar instead of using the ctek. Has anyone else looked at MPPT and observed the difference between a simple solar controller and MPPT?

On roof of 4by, I have 5 x 20w panels, and I borrowed 2 x 59w panels from a friend. These are 20 years old so I was expecting reduced output. Each array has twin 6mm cable to 50 amp Anderson plugs (genuine) , connecting to a y cable of 8 AWG with 50 A Anderson on each leg connected to the ctek solar input via a short 6AWG lead again with a 50A Anderson. Output was via a 1.5 meter of 6 AWG to a battery (in a plastic box with lid) with 50A Anderson. My panels produced more current then the borrowed ones

James

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Reply By: Member - Boobook - Tuesday, Jan 11, 2011 at 21:14

Tuesday, Jan 11, 2011 at 21:14

There are lots of threads on MPPT and efficiency. It is not clear from your post what the power output of the panels are or the voltages when you observe 10A and 12A.

There is definitely something wrong if you see more amps without a reg than with the MPPT. What is the battery voltage?

AnswerID: 441523

Follow Up By: sup8pdct - Wednesday, Jan 12, 2011 at 17:30

Wednesday, Jan 12, 2011 at 17:30

The ctek was producing about 14.4 volts, direct connect was the current battery voltage which was about 12.4.
I didn't leave the xolar direct connected over night. I put the ctek back in line and moved the borrowed cells to catch the morning sun if there was any then direct connect when I got up.

James

FollowupID: 713700

Reply By: Robin Miller - Tuesday, Jan 11, 2011 at 21:25

Tuesday, Jan 11, 2011 at 21:25

Hi James

What you observed is entirely possible with correctly working non-faulty equipment.

Won't comment directly on the product you used , but from a design engineers point of view there are some points that one should be aware of using these things.

1st They can and do work and on the whole can give in the order of 10-15% improvement.

2nd They are essentionally just intelligent switchmode convertors and have losses and a practical efficentcy of roughly 85% - hence it is possible under some(only) circumstances to get more charge via a direct connection rather than via a PWM or Mppt solution.
However a direct connection will not protect your battery from overcharge and other issues.
Some naughty people even take out the protection diode in their panels to get that little bit extra as well, but they need to be prepared for sunset.

3rd There are Mppt convertors and Mppt convertors - some will not track and deliver the max charge when the input voltage drops below about 14 or so as with PWM units whereas a direct connection will put charge into a flat battery even.

AnswerID: 441530

Reply By: CSeaJay - Wednesday, Jan 12, 2011 at 22:17

Wednesday, Jan 12, 2011 at 22:17

James

I too have problems with the CTek

When hooked up to my 80W solar panel, in full sun, all the lights that should be on comes on:
The poer light, the solar light, and then the charging light to the battery.

Then after 10 seconds, the error light flashes, and the process starts again.
Took it in to my local Battery World. They tested my setup - all good. They wired a new CTek on - same symptoms
They were puzzled, called someone with more knowledge, and was then advised that the 80W panel was "a bit light' for the CTek which needed more Watts (or Amps - cn't remember)

Cheers

CJ

AnswerID: 441629