New 12v Electrics – Total Charging Solution

You may also like...

40 Responses

  1. Craig Ross says:

    I’m currently doing a split charge system in my vivaro (more for work purposes than camping) I am now looking for a 240 charger, that I can plug in when Van parked on drive to charge my two 110 leisure batteries. Which charger would you recommend as I know you have done a lot of research on this matter.

    • David Black says:

      Hi Craig. If your looking for a very good charger then the two I would recommend are the Numax Connect & Forget 20a which is about £95 or if you can stretch to it the CTEK MXS 25 which is about £180. I’ve tested both of these chargers and both are great. The Numax charges at up to 20a per hour and the CTEK up to 25a per hour. You could look at a lower amperage version of either of these to save some money but they would charge much slower. Hope this helps, David.

      • Craig Ross says:

        Thanks David,
        I have done alot of research today and I think the MXS 25 is expensive but most likely worth it! So think I will give one a go.
        How is your camper coming along? Do you mind me asking what you do as you are hoping to use the camper for work too if I am correct?

  2. David Black says:

    The MXS 25 is what I have fitted, as you say it costs a little more but it’s a great charger. My van is coming along really well. I have quite a few articles almost ready to publish and a few more videos nearly finished, should have them on here within the next week.
    My work is a little varied. I own an online replacement kitchen doors company that pays the bills and I write articles here and there on a couple of subjects. I prefer the writing tbh but it doesn’t pay enough to do full time.

  3. Panayiotis says:

    Hello David, congrats on your work!!!! It is actually very professional…
    Just a short question for my understanding. By using the great ctek stuff means that you do not need an MPPT for your solar panels anymore????

  4. baz taylor says:

    What size/rated busbars did you use? I understand the nasa bm1 comes supplied with the correct shunt but my knowledge isn’t great so don’t know what busbars I should us, thanks. This is a genial set up!

  5. jamie says:

    Awesome stuff. I love the sound of this and might go this route. Just to clarify on parts:

    x 1 ctek d205s
    x1 dtek smartpass
    x 1 mxs 25
    and x 1 Nasa BM1 for monitoring?

  6. Gary says:

    Great blog. You’ve helped me a lot with planning my build.

  7. Doug Sassaman says:

    I really like your set up, and am considering using the Ctek D250S + Smartpass for my own (similar) set up. I can’t find many reviews for the Ctek product online – perhaps you could fill me in on how well the set up is working? It seems that I can get the D250S and Smartpass for the same price as a nice 40A MPPT Charge Controller, so I’m a bit hesitant, and have a feeling it’s “too good to be true”. The only real difference I can see between this set up and a nice MPPT Charge Controller is that the max. input voltage on this is 23V, while some MPPT controllers allow upwards of 150VDC… but charging voltage and amperage seem to be similar. How is yours working out so far?


    • David Black says:

      Hi Doug, mine has been absolutely flawless – true fit and forget. My (cheap) batteries are still fine and it keeps my starter battery nicely topped up. If I were building another van I’d use exactly the same setup.

  8. ben hughes says:

    hi david
    looks like your system works really well and largley due to you thourough research and thinking!
    Im embarking on our 07 sprinter conversion , started 2 years ago with windows fitted and a roof light.
    I now have time to continue and want it up and running asap.
    Trying to decide on charging solutions and electrics is as you say tricky….
    I like the look of the d250 s , we only want to run 12v lights, a 50 litre compressor fridge,(weaco crx50) , and have ability to charge phones , and a laptop. Also have ability of ehu charging (v occassional or at home use)
    I have 2 x 100 ah leisure batteries. plan to fit d250s , .and 2x 100w solar panels.
    In your opinion would this provide enough amps to keep the system running? basically im hoping i dont need the smartpass as our consumption will be minimal , (really mainly the fridge).

    Would welcome your thoughts based on your experience with this system.
    Many thanks

  9. chris stapledon says:

    Hi Dave. This info has been great. I have a vintage Citroen H Van converted to a camper and I installed a split charging system and leisure battery myself using a voltage sensitive relay. However, i keep getting flat batteries and can’t work out where the issue is. So I had decided to go back to the drawing board and I am going to base it on your system but with 1 leisure battery rather than multiple. Your wiring diagram is great. Can you clarify for me, should the negative bus be grounded to the chases at all? If not, is the only ground in your system that from the negative of the starter battery? Thanks again for the help.

    • David Black says:

      Hi Chris, in my setup the system is grounded from the starter battery and the leisure batteries. I didn’t ground the negative bus bar – from memory this was something to do with the Nasa monitor. Could be wrong on that, just from memory. Good luck sorting it out, David

  10. Les Flockhart says:

    Hi. I am very pleased that I stumbled on this post as I have been looking for a system for charging my leisure batteries. I do a lot of wild camping in the UK mainly because of my love of wildlife and especially at night time. I have been using a split charging system plus a 100W solar panel to keep my batteries charged and a smart charger to top them up when back at home. My two 110A leisure batteries have just given up on me after 3-4 years so I am looking for a different system. Whilst watching wildlife I use my laptop and night vision cameras with pan and tilt functions and I draw about 5-6 A for about 5-6 hours and on top of that during winter I have an Eberspacher diesel heater (I forget how much current it draws). What sort of system would you recommend to suit my needs especially for the winter months as it is a time where I use the most current. What type of batteries do you use and long do they last? I am planning to go away shortly and need to replace the present ones. I have read many articles on batteries and it seems traction batteries are more suitable, but this comes at a great cost. Any advice is greatly welcome. I am looking forward to take early retirement next year and build a bigger van so add a few extra AHr for a compressor fridge. Les

  11. Ben says:

    Hi David. Massive thanks for the website. I was already half way through my build when I found it and coincidentally we seem to have gone with virtually the same setup with the same experience – even down to having a rather large and expensive Sterling B2B charger that I decided against using! So it was great to pop on here and cross-check my plans against yours.

    One thing I can add for interest is that I have found the CTEK can handle more than 23v solar input. My panel is rated at 23v max output but in practice I have found it consistently puts out 28v in direct sunlight. After 5 months of use with the CTEK it’s still working brilliantly. I may be shortening the life of the unit of course, only time will tell, but I think this is very unlikely because it is usually current that kills electronic components, not the voltage.

    I did cynically wonder if they only limit it to 23v because they want to encourage people to buy the more expensive heavy-duty devices from their range. 23v is incredibly low compared to equivalent solar regulators on the market.

  12. Paul says:

    Hi David,
    Could you clarify something for me? I would like to use the d250s/smartpass system, but my van is a 2013 boxer and therefore Euro 5 compliant. I have been advised that this will mean it has a smart alternator. Your van is post sept 2009 (euro 5 inception) so I guess this is the same? The CTEK d250s does not work with the smart alternator, and a modification is required, which is outlined on the CTEK website. However no mention is made of using the d250s/smartpass combo with a modern alternator. Does this mean that the smartpass works fine with the smart alternator? There is no mention that I can find anywhere in the specs for the smartpass that mentions this issue, yet it is clearly mentioned that the d250s is incompatible. I am worried that the smartpass will also be incompatible, as the recommended fix for the d250s is NOT the addition of a Smartpass….. In which aces why is the issue not mentioned anywhere in relation to the smartpass?! I would value your thoughts. Thanks Paul

    • Paul says:

      For anyone who reads this blog and needs to use the d250s/smartpass combo with a variable voltage alternator, I have managed to get some advice from an Oz supplier (CTEK are popular down under). Refer to the CTEK website for basic info, they have a wiring diagram for the d250s alone. You will see that an automotive relay is used between the sources and the charger. If you are using the smartpass as well, the only difference is that switch contact 87 is wired to the alternator-in post on the smartpass as well as to the positive starter battery. Note that it is NOT connected to the alternator-in post on the d250s.
      This is not the best system for modern vehicles as there are alternative battery to battery chargers available which have up to date technology that work seamlessly with smart alternators without the need to add extra relays to make to product work and mess about splicing into the ignition loom on your expensive new van.

  13. Rob Wilkinson says:

    Hi David,
    Thank you for these gems of information. I’m wearing my fingers out on the keyboard researching van conversion electrics. I can see this system would work well but would it work with a ‘smart alternator’ which under braking can increases voltage to 16v+ and down to 10v under acceleration? Thanks. Rob

    • David Black says:

      Tbh I’m not sure Rob. I see that Paul has made a comment about this below as well.

      • Paul says:

        Hello Rob and David,
        Since my original post(s) I have had the opportunity to chat to CTEK and done some research on my own charging system.
        To be honest I did not originally understand quite how the Smartpass works. The D250s is a 20a charger, which is inadequate for a 400ah system, as David says. The intesteresting thing is that the Smartpass is just a relay. It claims it can charge batteries at up to 100a rate by boosting the D250s, but what in fact it does is just allow alternator direct charging to leisure batteries until absorption phase, in other words it’s just a ‘smart’ switch, switching from alternator direct (just like a very simple and cheap VSR system) to the D250s. When the bulk charging has been done via alternator, the D250s takes over, so in fact when the difficult part of the charging cycle is operative, the D250s is working alone.
        I had a chat with CTEK and they state that the Smartpass with D250s combination is not compatible with smart (variable voltage) alternators, but they are bringing out a new product in 2017 which will meet that need.
        I ran my van with a voltmeter on the battery and discovered that in fact it held a steady alternator charging voltage of 13.7v – therefore my 2013 Euro 5 van does NOT have a smart charging system. Hope this is of use to someone else. Great news for me as charging leisure batteries from a smart system is a nightmare. Although there are products available that claim to cope with this, the reality is that the alternator is off for much of the time and therefore is producing no charge at all.
        If you do have a smart charging system on your van the only option is to get a B 2 B charger designed to cope with low alternator input voltage, such as the Redarc systems (Australian) which are available in the Uk, and have inbuilt mppt solar trackers. Another option is the Sterling products, but they do not include in-built solar controllers. This is not necessarily a bad thing, as the CTEK controller in the D250s is very poor according to test results I’ve seen, but more expensive doing it all separately of course.
        Good luck with it!

    • Paul says:

      If you have a smart charge system that controls the alternator output via the ecu the D250s/Smartpass combo will not work. This is because the ecu monitors the voltage requirement on the main vehicle systems and makes sure this is supplied via the alternator (it is a common misconception that it is the vehicle battery that supplies this charge), such as current draw for headlights. Once the starter battery is charged (within a minute or two of setting off) the alternator output drops off, sometimes to zero, depending upon what you are running. Even the smart chargers designed for variable voltage alternators generally only boost voltage from a minimum alternator supply of 9v or so. So for a lot of the time whilst driving a modern vehicle will supply insufficient voltage to a battery to battery charger to allow secondary battery charging. This is true even for so a called smart chargers. This is especially true for the CTEK units as they are designed to cut out if the input voltage drops below about 12v (11.5v?) in order to prevent battery discharge. I think this sort of technology is going to catch up with the emissions bandwagon soon, but in the meantime it’s a pain in the arse.

  14. Bill says:

    Hi THere,
    i have bought a motorhome recently and bought 230ah battery with 2x100w solar panel , would you say this combination of products will work or i could do with something else as well ?
    x 1 ctek d205s
    x1 dtek smartpass
    x 1 mxs 25
    and x 1 Nasa BM1 for monitoring?

    MPPT is enough?

    Thank you so much

  15. Reece says:


    An excellent article and you have provided some very useful information!

    Just to clarify, I have 3 ways of charging: Solar, Split Charge, EHU.

    The control module you have recommended climates the issue of overcharging and maintains the battery health (TEK-D250S).

    My question is how do you switch the 12v off all together and change to EHU ? I assume you have a smart charger on the EHU side to also maintain the battery health.


  16. Nathan says:

    Hi David – I am putting together my wish list for a conversion and have a power hungry family of 4 – so wondered how you have been getting on with just the 2 x 100W solar panels? Did you need to fit the 3rd ? Also I have been seeing blogs where people are pumping electric hook up power straight into their CTEK onboard chargers on the same alternator input without the need to install a separate CTEK MXS25 too ? Presumably you ruled this out ? Cheers

    • David Black says:

      Hi Nathan. My plans are changing so the van is being rebuilt with LiFePO4 batteries. Sadly the CTEL’s don’t work with LiFePO4 so are going (real shame, been so good).
      I’ve found 200w is fine in the summer months and a few days (I use a lot of power), but upgrading to 400w in new build. Thanks, David

  17. David Detts says:

    Hello David. I have been building a campervan for the last year or so, it’s entirely to my own design and to my requirements , I’ve used a low mileage Relay I found and I’m building it with long term travel in mind for two people only, building and conversion is no problem to me as coach building and conversion is my background although not motor homes . My knowledge of the most up to date electrical systems is where my weak point is, I’ve been looking at your progress in this area for a year or more now and find what you’re doing is the best I’ve seen by far, I already use Ctek stuff on my cars and am aware of its quality, I intend to use the advice you give on my own vehicle which has to be finished by July . I am installing roof mounted Aircon , my batteries will be three 135 ah.
    with solar panels , I am following your progress and will be purchasing all the Ctek stuff in the next couple of months . I have taken a photographic record of my build to refer back to, I don’t tend to go on forums and display what I do but I do follow your build progress because your electrical knowledge is the best I have come across and I’m very pleased I found you.

    • David Black says:

      Thanks David. The CTEK chargers have been great and I’ll be sad to see them go (moving to LiFePO4 battery which CTEK doesn’t work with). Good luck with your build, David

  18. Dave Betts says:

    Where are u sourcing your LiFePO4 from? The one’s I have been looking at with equivalent capacities are around ten times the price.

    • David Black says:

      Have a look at They sell the same cells as I’ve used. They also sell the BMS I went with (Smart123). The people who made the BMS are releasing a smart relay that can be controlled via the BMS as well (to cut loads and charging if at dangerous levels). I’m waiting for this to arrive, then will show the system all working 🙂

  19. Francis Boundy says:

    Hi David

    I’m looking at a similar conversion and keen to look at the LiFePO4 cells that you are using. What solar controller and charging solution are you using / planning to use with them?



  20. Mike says:

    Hello, thanks for all the great info and content…..I have a BIG problem……….
    I am nearing completion of my van build and at the point of finalising the electrical installation.

    I have a 12v /450Ah battery bank and the ctek d250s dual and smartpass and a single 300w solar panel on the roof.

    I’m very new to the 12v / solar world, so my knowledge is also very limited. Due to this I connected my solar panel to the d250s today and I think I’ve broken it only after checking the output voltage of the panel did I find it that it was 36v…. And reading the instruction manual for the ctek,v the max input voltage from the solar panel or can take is 23v……bugger! Other than getting new (smaller) panels or completely changing my set up, is there anything anyone can think of to get me post this problem? Obviously the ctek will need fixing/ throwing away.

    Cheers, mike

    • Paul says:

      Bit late Mike, only just re-visited this site. The Redarc b2b chargers will accept that voltage I believe. The redarc does pretty much the same as d250/smartpass but in one small unit, and only provides up to 25/40/50 amps depending upon which one you buy, however I would have thought that would be sufficient rate of charge for most users. If you are running an alternator & solar charging system you will also need the redarc RK1260 relay which allows auto switching between solar and alternator. It prioritises solar. It will also do lithium batteries.
      I have had the d250s/smartpass for 2 yrs and the d250s has already broken and in a very bad way – it stopped regulating solar charge to my 400ah battery bank, I checked on the van the other day and the batteries had boiled to death with a charging voltage of 17+ volts from a 200w 23v panel. So that’s. Cost me over £1000 in batteries and charge system thanks to CTEK.
      I’m afraid your d250s will be damaged with 36v input.

      • Paul says:

        Edit – sorry, looking at your battery bank capacity 40amp charging will be inadequate, depending upon usage of course

  1. September 17, 2013

    […] If your looking at possibly getting a B2B charger and also possibly solar it might be worth looking at the CTEK D250S Duel and Smartpass. The D250S is a great battery to battery charger that you can also connect solar panels directly too (it has a MPPT solar charger built in) but only charges at a maximum rate of 20a. If you add the CTEK Smartpass it charges at up to 100a. It also keeps your starter battery topped up. I have this system going into my own van (fitting 4 x 100ah batteries) and did a ton of research before deciding on this set-up. I've written a small blog post which has a video showing how the units work here if your interested:…ging-solution/ […]

  2. December 23, 2013

    […] battery when the leisure batteries are full. I have this system and wrote a little about it here:…ging-solution/ and here:…-review-video/ if your […]

Leave a Reply

Your email address will not be published. Required fields are marked *