Cotek ??? Never again...

mathiasmathias Registered Users Posts: 31 ✭✭
Well, everything is in the title, but for those interested i will explain why...

This is my first post here, even if i spent hours reading questions and precious answers when i built my system together. So thanks for this forum. I learned a lot here and here's my little piece of advice.
One and half year ago, i put together a 48v off grid system for our small resort in Sarawak, Borneo.
1500w of panels, a Kid, 4x 12v 240A batteries in series, DC breakers... then came the choice of the inverter... Ouch, the good ones are SO expensive !!! So i was left with cheap chinese or middle prices options...
I choose a Cotek (SK 1500). It worked OK, even very well, 24/7, for... a bit less than a year !
A bit disappointed, i checked and the warranty is 2 years. I contacted the website where i ordered it (Ecodirect) : no answer...
Then i contacted Cotek Americas. They asked me for the serial number. Then they explained me that this unit was manufactured more than 2 years ago, so no warranty possible ! I started to get nervous and explained than i BOUGHT it less than 1 year ago, i don't c... how long ago it was MANUFACTURED !!!
So, they agreed to pay for the repairs. I was given the choice to send it to the Malaysian distributor or to the Cotek factory in Taïwan.
They warned me that repairs should cost about 120$ : how can they know that ??? Well...

Eventually, it arrived to Taïwan. They checked it and found a bit of dust and some rust inside, so they told me that this was an "user abuse" (!!!) and so refuse to repair it for free, asking me 1/3 of the price to fix it !!!

I live on the coast, and all the setup is in a shed. But this brand is sold worldwide, including in many shops selling boats accessories, and their sales speech includes "boat" in every descriptions i found. Is living on the coast worst than on a boat ??? I am also a sailor, and the 2 cheap chinese inverters i have on board are doing great after 2 and 4 years, and they cost me 20$ ! Ok, they are 150w, not 1500w psw.
In my place, every others electronics i have (computers, phones, tablets, washing machine, the Kid...) are doing great, even if they are not advertised as OK to be used on boats !

So, they build [bad product--Bill B.], sell it quite expensive, and when it fails under the 2 years warranty, they just don't want to hear about it (i found on the net others having the same kind of problems...). Not very serious, and talking of "user abuse" like if i did throw a bucket of salt water on it !!!

So in the end i am stuck with a cheap chinese inverter until i am rich enought to get a good one... But if it fails before his first year, i'll blame me : it's only 1/10 of the price of a good one !!!

Ps : sorry for my English, i am French...


  • BB.BB. Super Moderators, Administrators Posts: 30,049 admin
    I am sorry to hear about your problems with Cotek inverters. Warranty service is important too. Cotek has been a reasonably priced/reliable inverter for many folks here on the forum.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • kaipo_boykaipo_boy Solar Expert Posts: 143 ✭✭

    Mathias, sorry to hear of your problems. I bought the same inverter, the SK 1500, and its been in service around 10 months now, perhaps a tad more. I haven't had problems with mine yet although its very dusty where I live. I just peeked in mine a couple days ago and noticed some debris inside, against the grate that the fan pushes air against... so I was going to take it apart and blow it out with air, but its mounted on a wall and not easy to take down to get to. I hope I don't run into the warranty problems you mentioned; very happy with mine so far.  It runs just fine up to 30.0v, and since I have my 24v batteries set at 29.6v for absorb, it JUST makes it under the wire, although I've had the turn the inverter off when doing any kind of EQ.

    Did the factory mention what component inside that failed? is it a common problem?



  • mathiasmathias Registered Users Posts: 31 ✭✭
    Well, i was of course very happy with mine when it worked ! No problems at all and very good surge capability (much better than the cheap chinese !)
    Of course i hope for those who own one many years of good service.
    Just wanted to warn people considering to buy one that the warranty is not to be counted on (as i said, i found i am not the only one with warranty problems), which i find very hard to accept !
    And also their claim that it's OK for marine environment as it's obviously not !
  • mathiasmathias Registered Users Posts: 31 ✭✭
    Apparently they talked about changing the whole controller card, which i guess is easier for them than changing components. They wanted 230$ for that...
    I did pay for shipping back though, and i will have it checked by a local electronician, if and how much would it cost to fix it. Will keep you updated.
  • westbranchwestbranch Solar Expert Posts: 5,182 ✭✭✭✭
    I have a 24V ST 1500, and am also happy with mine, there are probably some consistencies under the covers of all 3 of these...  Mine is a 'hard wired' version, ie no plug in  sockets.... 
    I have been on their web site recently and see that my ST model type (ST stands for sine wave, transfer switch)  is no longer available and wonder is that a function of demand or a result of failures??? 
    Mine was in 24/7 use for 8 months last year, nary a blip!Just last week I tried starting my Makita 10A air compressor, NO GO! it makes my 3000w gen suck wind... so obviously > 3000W surge...

    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    Interesting, inverters for the most part tend to fail either in the first couple of weeks, or much much later.

    But if you decide to upgrade, this is the kind of thinking you might want to consider... Generally for off grid hard wire, (and  out of the way sites especially) you want low frequency inverters. Cotek and Samlex make both HF and LF inverters. The LF ones have a much bigger transformer inside and tend to weigh 10s of kilos. Those SKs clock in under 9kgs, so its pretty clear they are HF models. You can also tell by the case form factor, flat as opposed to boxy. Another clue is the absence of power outlets on the unit.
    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,

  • mathiasmathias Registered Users Posts: 31 ✭✭
    Well, we all learn, and usually faster when it gets to the wallet !

    This model is 7kg, so obviously HF. This was not a deliberate choice from me, just the max money i could afford at the time.

    We don't live in a perfect world, and i can accept that manufactured products can fail, even the best ones.

    What i don't accept is the complete denial of responsibility from the company, finding excuses twice so they don't have to honor their warranty offer, even worst : saying in fact that if their product (used as they prescribed) fails it's not their fault but mine !
  • 2twisty2twisty Solar Expert Posts: 199 ✭✭✭
    I don't mind the Chinese solar panels, but for my CC and inverter, I went with US-Made components. My wallet screamed.  It wailed.

    But I have confidence that if I ever need service (in warranty or out), I won't have to send the thing to Taiwan and deal with people who try to squirm out of their word.
  • PhotowhitPhotowhit Solar Expert Posts: 5,105 ✭✭✭✭
    I think you might have just gotten a bad apple, it happens. My Prosine is a high frequency inverter and it's been 24/7 for nearly 10 years, only problem was replacing a fan, by me, not rocket science. On top of that my inverters, when in use, live only protected from rain, outside in a 'power center' about 1'x4'x5', though the Prosine are made for marine environments.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do
  • boBboB Solar Expert Posts: 975 ✭✭✭✭
    corrosion in the circuits are much more common either being on a boat or near the shore of salt water...  This is why they should conformal coat the board and components...  To help reduce this issue.  Do you know if the Cotek has this ?  They can't CCoat the  connectors because it would insulate those connections but everything else should be  coated.  I thought that Cotek was good to go in this regard but maybe not ?  I'm guessing of course that this is the problem with this unit but it is very possible.
  • mathiasmathias Registered Users Posts: 31 ✭✭
    Obviously no coating (see picture, and remember : less than one year in service !!!)

    Inverter is now in a local electronic shop, i'll know soon if they can fix it (and for how much...)
  • vincevince Registered Users Posts: 79 ✭✭
    I also had an sk1500-248 fail after only a few months of use. Had no problems getting it replaced under warranty. Was treated very fairly without complaints.
    Sunpower 3 x 435 watt panels, 48 v 215 AH battery bank (Sam's club), Midnite Kid and WBjr, Fujitsu 9RLS3 split duct AC, Outback FX 3048T + transformer 2000W 120/220V, GrapeSolar Fridge.
  • mathiasmathias Registered Users Posts: 31 ✭✭
    Lucky you Vince ! I really felt being treated like shit !

    More bad news for me, the local electronic repair shop can fix 12/24 volts inverters, but they never saw a 48v one and after few days declared that they can't test it as they have only small batteries that they can put in series and they think it's not enought amps (no, i am not going to bring them my 4 batteries, i have no road access, everything come by boat...) , so they decide they can't fix it... Go figure ! I like living in Asia a lot, but some days it's hard to understand how people think...

    So, as i am not a good electronic guy, it's probably over for this unit...
  • COTEK_SupportCOTEK_Support Registered Users Posts: 2
    Hi Mathias, I just saw your post here and thought I should respond on behalf of COTEK in North America. I am sorry that you had a poor experience with your defective SK1500-248 in Asia. Our responsibilities for the USA & Canada is to ensure that our customers are dealt with in a professional and satisfactory manner according to the terms of the warranty. COTEK is the premier manufacturer of battery-based pure sine wave inverters and we have 19 different private label companies globally that are proud to put the name on our products.

    However, we do still have failures - approximately 1/2 of 1% of our inverters fail within the two year warranty period. When this occurs for our larger units, we have them sent to our service center for evaluation. Once tested and verified that the unit is defective and the failure was not caused by the operator, then we send a replacement unit to the customer. This process typically takes 10-14 days. For our smaller units we have the unit sent to our US warehouse and send a replacement immediately.

    I hope this helps to clarify the process.

  • mathiasmathias Registered Users Posts: 31 ✭✭

    Well, thanks for your input, but it doesn't clarify anything for me !

    Re read my first post : Cotek Americas first answer has been a refusal of warranty as unit was manufactured more than 2 years ago. Only after i complained about purchase date mattering more than manufacture date did you agree to take care of the repairs. What if i didn't complained ?

    Then, it's about Cotek Taiwan, not you, but i really felt treated like shit : i was told exactly that all is my fault ! I just used this unit as it was stated, but still if there is a priblem it's my fault. I'd say if you want to sell your products to boat owners, then coat the boards and all will be fine... No, itns my fault if it's not coated...

    As i already said earlier, i'm not complaining here about quality, but about how poor your customer service has been with my case.

    I am now running a cheap Chinese inverter, oversized to get past the surges, and without no load function... 2 things i am not really happy with... But i live with it and if the cheap thing outlast your product (remember, my Cotek lasted about 10 months...), then i will say that i prefer cheap chinese products over your cheap sense of business..

    Mat, your disatisfied customer
  • South AfricaSouth Africa Solar Expert Posts: 295 ✭✭✭
    edited July 2016 #17
    Just a thought.

    COTEK_Support, respect for stepping in.

    Lets say mathias has a legit claim, and I not saying he has not, why not jump in and assess the situation first hand? 

    Cotek could lose for this forum is picked up by Google searches.

    Case point:
  • COTEK_SupportCOTEK_Support Registered Users Posts: 2
    Well Mathias, I am not sure who you dealt with in Taiwan, but they usually have better customer service than that. Our office in the USA has product that has been fixed by the factory and returned to us. I would be more than willing to offer you one of these, as a way to mitigate your negative feelings towards COTEK. However, we do not have any 230V product. Would you have any use for an equivalent 115VAC model that has been repaired by the factory?

    Please advise.
  • mathiasmathias Registered Users Posts: 31 ✭✭

    Well, i sure wasn't expecting that ! Didn't even know that you guys would read forums...

    I could list here names of people in Taiwan who dealt with my case, but not sure it's appropriate...

    For sure, your offer is more than welcome (i'm not sure but i suppose i could use a step-up converter to go from 115v to 230v AC, even if that would probably mean a bit more losses) !!!
    And yes, that would definitively change my point of view (and advice to people asking questions about my setup, what to buy and what not).
    Thanks again, let me know how to proceed.
  • South AfricaSouth Africa Solar Expert Posts: 295 ✭✭✭
    And that is how we roll.  :)

    Mathias, list the names in a private message to Cotek. Legitimate customer feedback is very important.
  • mathiasmathias Registered Users Posts: 31 ✭✭
    Hi South Africa,

    I already sent him a PM. I will give him names if he wants. :wink:

    Anybody would like to comment on the use of a step up transformer 115v to 230v AC plygged in a 115v inverter ?
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    mathias said:
    Anybody would like to comment on the use of a step up transformer 115v to 230v AC plygged in a 115v inverter ?
    I assume that the 115v is 60 cycle... after stepping it up it will still be 60 cycle.  Whether that is a problem will depend on your loads, which I assume are expecting 50 cycle.

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • mathiasmathias Registered Users Posts: 31 ✭✭
    Thanks vtMaps,
    Good point.
    A quick search i found these :

    Too small... They talk about 50/60hz, but i don't understand if it change the input hz or just accept both...

    This one is 1500w, but i guess peak power. They don't mention hz...

    I don't rhink my loads are very sensitive but admit that i don't know much abouth frequency...
    I have lights, small (15/20w fans, seldom used), mobiles/computers/cameras chargers, washing machine and a freezer converted to fridge.

    Now that i think about it, my Cotek inverter had a switch to select 50 or 60hz. If same model then should not be a problem...

    What about inverter losses plus converter losses/ total efficiency of such a setup ?
  • BB.BB. Super Moderators, Administrators Posts: 30,049 admin
    I would avoid the step up (boost) transformer. That adds more costs and energy losses and does really do anything "special" for you (you do not need 120 and 240 VAC for your installation--I believe). Roughly 5% more losses for transformer--And larger transformers (if you cannot find a small one that matches your inverter) can over current an AC inverter while trying to start up.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mathiasmathias Registered Users Posts: 31 ✭✭
    Thanks Bill for commenting.

    For sure, i wouldn't buy a 115v inverter plus a transformer to power 230v loads...
    But considering the situation, and my wallet, a more efficient inverter coupled with a transformer or a really inefficient chinese inverter, well... I have no idea which configuration would be best !
    All i know is that at least i would have a spare, which i believe is always better than not !

    I am corresponding with Cotek Americas and will keep you posted.
  • BB.BB. Super Moderators, Administrators Posts: 30,049 admin
    edited August 2016 #26
    The 230 VAC inverter is your only cost effective choice. It (the transformer) will add "unneeded" losses and complexity to your system.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mathiasmathias Registered Users Posts: 31 ✭✭
    Ok, ok...
    It's hard for me to refuse a free inverter, but for sure i get your point...

    I hope my cheap chinese will live long...
  • softdownsoftdown Solar Expert Posts: 2,914 ✭✭✭✭
    Sorry to change the subject a bit but the line of reasoning has been presented.

    Back up inverters? I have a back up 24 volt system in case my 48 volt system crashes. I keep a lot of frozen and refrigerated food. Bought a Cotek inverter after talking to a satisfied forum user.

    The problem with back up electronics? It seems that capacitors can age poorly....even in storage. This problem has grown significantly worse due to modern changes in electronics.

    In "mathias" case.....sure....a "free" back up inverter? Of course...jump on that. Though it wasn't truly free. 

    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • BB.BB. Super Moderators, Administrators Posts: 30,049 admin
    He lives in a 230 VAC 50 Hz power country--And the offer was from North America Cotek support with a 120 VAC 60 Hz inverter.

    In this case--Not useful to him without a step up transformer (more costs, more expenses, etc.).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mathiasmathias Registered Users Posts: 31 ✭✭
    Yes, always happy to have spares...
    I'm corresponding these days with head of Cotek Americas, who is more than willing to offset the poor service of Cotek Taiwan.
    Due to differents time zones, week ends and holidays, it's a bit slow...
    Of course, they don't have much on hand with 230v ac output, but they offered me some differents choices, from small new inverter to medium size factory repaired, even a big 3000w that they would sell me a very reasonnable price (but... No thanks).
    I choose a 12v/230v 1000w.
    Quite different from original inverter, but at least something i can use, either reconfiguring my bank, most probably as part of a second setup.

    I am waiting for a quote for shipping, they offered me shipping only to US, far from Borneo where i live...
  • kc8adukc8adu Solar Expert Posts: 45 ✭✭✭
    so they cannot just send a replacement card?
    its not that hard to swap it if it has plug in connectors.
    but having never seen a cotek its hard to say.
    as for capacitors run the spare occasionally to keep them formed.
    i tend to just replace them if they are a known cheap brand.
    many noname caps are trash from new.and its beyond stupid to not conformal coat boards in a product that will find itself in a marine environment.or in an unconditioned space like a solar power system.some bean counter got a pay raise for saving $0.10 per unit only for the end user to pay the price in the form of a easily preventable failure!
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