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eb145's avatar
eb145
Explorer II
Jan 05, 2014

CTEK D250S DUAL - MPPT and dc/dc battery combo charger

Does anybody own one of these?

CTEK D250S Dual - MPPT and dc/dc battery charger

You can buy it for $174 or $274 on Amazon.

It should be useful for 2 purposes for a TT or 5th wheel:

1. MPPT charger for solar panels.

2. When hooked up to Tow Vehicle charge wire, it also acts as a battery isolator and at the same time, a dc/dc charger that boosts the voltage at the trailer battery so it will charge at higher rate. This overcomes the long-thin wire from TV alternator to Trailer battery.

For some reason it seems this type of DC/DC charge functionality is more popular with boondockers in Australia and Europe more than the US.

Has anyone tested this setup on a TT or 5th wheel with just the standard 7-pin RV connector?

This review is on Amazon for this product:

"It's a Battery Isolator, no cutoff needed, It Charges the Battery in depended of engine battery, it has the solar controller built in, wont overcharge the battery with the temperature probe, It's a must have for RV Trailers as the voltage is low by the time it gets from front of the vehicle to the battery in the trailer, plus add a solar panel on top, your all set."

EDIT: changed name of product to be more accurate "D250S Dual"
Thanks,
Ed
  • eb145's avatar
    eb145
    Explorer II
    Jan 06, 2014
    CA Traveler wrote:
    Now I'm even more confused. If it's intended as a isolator as in charging 2 battery banks then every MH I've owned has one. Trailers on the other hand don't normally have 2 battery banks and hence don't need a isolator.

    By isolator do they mean it disconnects the tow alternator from the trailer? That function is very common in the US. As a DIY project a $5 relay will do the job. And I'd guess that most factory tow packages supply 12V only when the engine is running.


    The primary feature that this thing is bought for is the ability to step up the DC voltage at the trailer battery, even with a long, thin wire from alternator to trailer battery. This allows improved charging of trailer battery from the alternator.

    It also has an isolator relay to isolate the trailer battery from the TV battery when engine is not running.

    It also has the MPPT solar controller.

    So it seems to be useful for charging trailer batteries from the alternator and as a solar charger - it just automatically selects the best power source for charging. It looks like it can also charge the tow battery from the solar panel also if trailer battery is fully charged.

    The Australians really seem to like dc/dc battery chargers like this.

    Ed
  • MrWizard's avatar
    MrWizard
    Moderator
    Jan 06, 2014
    maybe 'tow pkg' wiring is Not as Common in Europe as here in the USA
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Jan 06, 2014
    Now I'm even more confused. If it's intended as a isolator as in charging 2 battery banks then every MH I've owned has one. Trailers on the other hand don't normally have 2 battery banks and hence don't need a isolator.

    By isolator do they mean it disconnects the tow alternator from the trailer? That function is very common in the US. As a DIY project a $5 relay will do the job. And I'd guess that most factory tow packages supply 12V only when the engine is running.
  • eb145's avatar
    eb145
    Explorer II
    Jan 05, 2014
    BFL13 wrote:
    Here we go again. A 22v max input MPPT???? You don't gain hardly anything with MPPT and 12v panels, so that's a waste of money. You can do that with a $13 PWM controller. But you do need MPPT for a 24v panel, but they have Voc more like 37v.

    It is beyond stupid to have an MPPT controller that can only handle 22 Voc. Even a 12v PWM controller needs more than that. A 12v panel usually has 21.9-22ish Voc at 25C and it goes higher in cold temps.

    Meanwhile if you have solar, who cares what the 7-pin is doing or not doing? The solar is working while going down the road too, so you already have extra amps from that.

    This gizmo makes no sense at all.


    I just asked the manufacturer for more detailed MPPT specs. They sell this mostly for the DC/DC battery charging feature so you can charge your trailer battery off the alternator without having to run heavy wire from alternator to trailer battery - very popular in Australia and Europe it seems. Maybe CTEK just "checked the box" on the MPPT feature.

    "check the box" means to add a feature in name only, the actual effectiveness of the feature is not so important.

    The fact that I can't find any real MPPT specs from CTEK is suspicious. Plus any measured results by real users on internet forums that I have found have shown poor performance.

    I'll post what the manufacturer responds with.

    Ed
  • BFL13's avatar
    BFL13
    Explorer II
    Jan 05, 2014
    Here we go again. A 22v max input MPPT???? You don't gain hardly anything with MPPT and 12v panels, so that's a waste of money. You can do that with a $13 PWM controller. But you do need MPPT for a 24v panel, but they have Voc more like 37v.

    It is beyond stupid to have an MPPT controller that can only handle 22 Voc. Even a 12v PWM controller needs more than that. A 12v panel usually has 21.9-22ish Voc at 25C and it goes higher in cold temps.

    Meanwhile if you have solar, who cares what the 7-pin is doing or not doing? The solar is working while going down the road too, so you already have extra amps from that.

    This gizmo makes no sense at all.
  • eb145's avatar
    eb145
    Explorer II
    Jan 05, 2014
    CA Traveler wrote:
    Thanks for the specs. I didn't see any text indicating it's a MPPT controller, perhaps I missed it.

    Wonder what 5 stage charger means? My Magnum is bulk, absorb, float, equalize and standby/


    Sorry for the confusion - I changed the post title to match the product more closely. CTEK makes more than one product with "250" in the name. "D250S DUAL" is the product I am asking about here.

    As far as 5 stages, they are pretty much the same 5 stages you list for your Magnum.

    Ed
  • KJINTF's avatar
    KJINTF
    Explorer
    Jan 05, 2014
    After looking at their web site
    Looks as if they have good quality offering
    A Swedish company competing for the European business

    We here in North America do not see the many really nice international offerings
    I have long been a fan of Sterling Power out of England

    Take a look at their web sites
  • CA_Traveler's avatar
    CA_Traveler
    Explorer III
    Jan 05, 2014
    Thanks for the specs. I didn't see any text indicating it's a MPPT controller, perhaps I missed it.

    Wonder what 5 stage charger means? My Magnum is bulk, absorb, float, equalize and standby/
  • eb145's avatar
    eb145
    Explorer II
    Jan 05, 2014
    CA Traveler wrote:
    It's a battery isolator not a battery charger and expensive. I didn't see any specs on the solar controller.

    Not for me.


    It is a temperature compensated 5-stage charger, battery isolator and MPPT controller. And the 5-stage charging can get its power from a solar panel or the alternator. It seems to be able to both step-up and step-down the voltage from both sources to do the 5-stage charging.

    CTEK 250S Dual specs

    And yeah, I don't see any solar Specs either. Just a Max input Voltage of 22V.

    Ed

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