Ctek D250S - solar input info and some "how to repair" info

Submitted: Saturday, Oct 18, 2014 at 19:55

ThreadID: 109852 Views:15982 Replies:1 FollowUps:11

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808

Hi all

Thought I should share this with the forum in case anyone else is silly enough to do what I did and it might save them some money if they know someone handy with a soldering iron and basic electrical knowledge. Please do not mess with it though if you don't. This forum does not want to encourage anyone unqualified to play with this kind of high current stuff. And it only applies to this specific situation.

I use my D250S Dual somewhat as a portable charger between my work Van and Caravan. Playing around with it (as I do) I managed to connect the battery in reverse to the output (charge side) of the unit. Well that did not help it a lot.

From that point on the input lights would come on if the Solar or Alternator inputs were "alive"" but the green power light would not come on and no charging output. Oh bugger and the $$$ signs started flashing. So naturally I pulled it apart to have a look see.

For those interested, the negative output terminal connects directly to a 30A standard blade fuse internally (plug in) and then has a normally reversed biased Schottky diode (MBR1035 10A 35V) directly across the negative to positive output of the charger on the internal side of the fuse. Theory being I guess the diode will cause the fuse to blow in the event of a reversed battery connection.

In my case the fuse blew but it also caused the diode to go short circuit - maybe that is also by design - but why not just blow the fuse by using a higher current (>30A) diode so you do not have to replace it ?? Anyway, beware that if the fuse has blown the diode needs checking otherwise you will keep blowing the fuse and or create worse results.

Replacing the fuse and the diode (hence the need for a soldering iron) brought the unit back to perfect operation. I just cut the diode off it's legs and re-soldered to the legs rather than have to de-solder it from the board. This could all be done by removing the bottom of the unit (6 screws).

Also for those interested as it was subject of a previous thread, the solar input cuts in around the 12V mark - this is not specified in the literature for the unit which only mentions the cut in for the Alternator input and the maximum limit of 22V for the inputs.

The solar input can therefore be powered (as I do) by any sort of suitable DC power source within the limits of operation therefore and not just solar. So if it is a fixed installation (eg. in a caravan) and you don't have solar you can rig to fit a power supply to it using the solar input to keep the batteries in good nick. It could even be as simple as a laptop power supply that has reasonable current output (eg 19V 3.5A is not uncommon which very roughly would equate to about an 80W solar panel).

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Reply By: Member - kwk56pt - Sunday, Oct 19, 2014 at 02:07

Sunday, Oct 19, 2014 at 02:07

thanks I replaced the fuse in mine but the solar output never worked again so now i will open it
up again and investigate the diode

AnswerID: 540525

Follow Up By: Member - kwk56pt - Monday, Oct 20, 2014 at 13:47

Monday, Oct 20, 2014 at 13:47

i did google buy australia for that diode and all the listings were in america so can I ask where you bought your replacement diode

FollowupID: 826498

Follow Up By: Nomadic Navara - Monday, Oct 20, 2014 at 13:52

Monday, Oct 20, 2014 at 13:52

Try Jaycar, they may not have the exact one but they will have a bigger replacement that would suit.

PeterD
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FollowupID: 826499

Follow Up By: 808 - Tuesday, Oct 21, 2014 at 12:13

Tuesday, Oct 21, 2014 at 12:13

Sorry for late reply

Short answer - for simplicity use anything better than 10A and 35V in a TO220 casing and I would use Schottky rather than standard diodes.

I used a higher rated high speed diode I had on hand as a stop gap.

Look on eBay for Schottky and you will find replacements with higher voltage and current eg. I found these - 2 Terminals Schottky Rectifier 40V 10A SBL1040 and STPS10L60D Power Schottky Rectifier 10A 60 Volts - about $4 each - I would trust these and use them myself if you are not in a hurry to get them.

I bought 5 x MBRF1060CT 10A 60V Schottky (about $6 to the door). Note these are a double Schottky (I have other uses for them) so you would need to make sure you use the right 2 pins when replacing the old single Schottky - Anode (Positive) to the pin that is connected to the fuse, Cathode (Negative) to the pin that is connected to the Positive output.

Important thing here for me is the diode meets current and voltage requirements - they chose 10A 35V in their design so anything better than that to me will be suitable.

Without knowing the thoughts behind their design, I thought about why they necessarily used Schottky - I figure any diode with high enough current rating should last long enough to blow the fuse and save the unit in a reverse battery connection state. My theory is that Schottky are fast acting so have a very fast rise in current in forward biased conditions and lower forward resistance as compared to standard diodes.

Jaycar have an MBR735 (7A 35V) for about $1.50 and MBR20100CT (a double Shotkky 20A 100V for about $15) - but I would not use the MBR735 as it is only 7A.

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Follow Up By: 808 - Tuesday, Oct 21, 2014 at 12:19

Tuesday, Oct 21, 2014 at 12:19

When you say your solar never worked again, are you saying that your Alternator input still works OK ??

If so there is a 30A fuse on each terminal in my unit - the 2 inputs and the output.

If you blew a fuse on the solar input that would be a different situation and not related to the output section of the circuit described here which applies to both solar and alternator inputs.

I did not investigate any further than the output section to see if anything similar applied to the input sections.

FollowupID: 826529

Follow Up By: Nomadic Navara - Tuesday, Oct 21, 2014 at 15:20

Tuesday, Oct 21, 2014 at 15:20

Quote "Without knowing the thoughts behind their design, I thought about why they necessarily used Schottky - I figure any diode with high enough current rating should last long enough to blow the fuse and save the unit in a reverse battery connection state. My theory is that Schottky are fast acting so have a very fast rise in current in forward biased conditions and lower forward resistance as compared to standard diodes."

The quickest blowing fuse in the world is a transistor. If you are going to protect the transistors in the output section of your device you need another transistor/diode that is at least as fast as the ones you are protecting.

PeterD
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Follow Up By: 808 - Tuesday, Oct 21, 2014 at 18:21

Tuesday, Oct 21, 2014 at 18:21

Hi PeterD

Good to see you sre stll out there.

Without debating their design reasoning, the only purpose the diode has is to blow the fuse to remove the reversed battery connection by someone not paying enough attention like myself.

So we are really splitting hairs on the speed of the diode or anything else as compared to the delay time of the fuse.

But I would always agree that someone smarter than me chose a particilar component at time of design so it is wise to not use anything of a lesser specifiction for direct replacement.

Ken

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Follow Up By: Nomadic Navara - Tuesday, Oct 21, 2014 at 20:02

Tuesday, Oct 21, 2014 at 20:02

Ken, if the diode does not start conducting quickly enough there will be a damaging negative pulse getting into the output stages of the charger before the fuse blows. If it is too slow blowing the fuse the quick pulse is enough to blow the arse out the equipment.

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Follow Up By: Member - kwk56pt - Wednesday, Oct 22, 2014 at 00:41

Wednesday, Oct 22, 2014 at 00:41

hello 808,
yes that's correct the alternator input still works. I replaced the blown fuse but it would not work. I suspect I shorted it when I was trying to connect the solar panels. I ended up buying a Morningstar regulator to get the solar working.

Having read your post I am thinking of having another look, maybe see if I can test the diode. It was some time ago but the d250s lights would come on and then cycle on and off again once the solar light flashed on. I will try I have spent a lot of time stuffing around trying to get it working and as the price of new ones is coming down I might just replace it if the diode thing is not the issue

FollowupID: 826562

Follow Up By: Member - kwk56pt - Wednesday, Oct 22, 2014 at 11:17

Wednesday, Oct 22, 2014 at 11:17

Hi 808,
thread 97348 details my issue. Mine seem to pulsate rather than charge.By this I means it seemed that when it sensed the current it would shut down and commence the cycle again. My issue is probably different to yours.

I checked my wiring and connections. I had 2 x 90w Lorentz panels connected. Both panels are working. Probably best easiest to buy another d250S and go from there.

The Morningstar regulator I now use is not a mppt unit and of course it probably is less efficient as its not intergrated with the alternator charging source. My panels don't have a regulator of their own. the charge symptoms seem to be the same as someone described when a smaller under 80 watt panel is used

FollowupID: 826572

Follow Up By: 808 - Wednesday, Oct 22, 2014 at 14:02

Wednesday, Oct 22, 2014 at 14:02

PeterD - I do agree with you and would never suggest using lesser spec for replacement

KWK56PT - yours is definitely a different problem and nothing posted here would apply. Easy option probably is to replace it ad you say.

Ken

FollowupID: 826573

Follow Up By: KenInPerth - Thursday, Oct 23, 2014 at 16:37

Thursday, Oct 23, 2014 at 16:37

KWK56P

It could well be there is nothing wrong with your D250S Dual.

Bill (Sandman) posted this in your thread 97348 - "Cycling would be normal as the batteries reach a fully charged condition as the Controller would be in "maintenance" (pulse) mode, so cycling on and off would be the normal expectation."

I could not find anything in the Ctek literature that I had, but I got the same result once the Solar input had fully charged the service batteries - the Solar light was pulsing on and off.

I contacted Ctek to see if this was correct operation and was told pretty much what Bill posted - reply as follows:

"Yes that is correct depending on the software to indicate that the primary battery voltage is still about the 12.7 Vdc mark.

If it is also if above the threshold it will charge all batteries connect to it both van and car battery. Once the voltage drops below the threshold then it wont but there will be on solar as well. In this position it isolates the start and secondary
batteries for protection."

FollowupID: 826646