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CTEK (40-186) D250SA 5 Step Charger - 12V - 20
- Obtains and optimizes energy from DC sources such as alternators, solar panel or wind power to charge battery
- Automatically selects best and most efficient source of up to 2 that are connected to the charger for charging battery
- Fully automatic 5 step charger adjusts the charging voltage and current according to the state of charge and temperature of battery
- Great for “off the grid” applications with its multi-step charging from alternators and solar panels
- Can be connected directly to solar panels without the need for a regulator
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The CTEK D250S Dual is a 5-step charger that automatically adjusts the charging voltage and current according to the battery state of charge and temperature – reducing a battery’s charge time. This charger obtains its energy from DC sources such as alternators, solar panels or wind power and optimizes this power to meet the charging requirements of different battery banks. It automatically selects the best connected DC energy source (of 2) for the purpose and switches between these energy sources to achieve high efficiency multi-stage charging.
A sensor on the charger senses the battery temperature and adjusts the required charge by increasing the voltage in cold weather ensuring the battery is fully charged, and dropping the voltage in hot weather to avoid the problems of overcharging.
This charger has the additional benefit of an auxiliary input which can be connected directly to solar panels without the need for a regulator, offering free power from the sun and a built-in Maximum Power Point Tracker (MPPT) that helps the solar cells produce power as efficiently as possible by taking the most efficient source of energy from the solar panels automatically, and then using the power to charge the battery. The MPPT searches for the most effective combination of solar cell voltage and current, which ensures that the solar and alternator function in unison to maximize power output. This charger is perfect for boats with one battery, boats with start & service battery, boats with start & service bank, campervans, caravans, RV’s and trucks.
The D250S battery charger has a 5 year Limited warranty
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Most helpful customer reviews on Amazon.com
And, I emailed CTEK a question on the voc (maximum voltage) rating (23 VOC) and asking about combining the input of both the installed on roof solar panels and a portable solar panel (yes you can, but they need to be parallel wired). They got right back to me with the answers. They're customer service and multi year warranty can't be beat.
Just make sure that the VOC for solar panels is 23 VOC or less. I've read that someone in Australia fried his d250s dual by hooking up a 36 VOC panel.
This product came highly recommended! The review on the Expedition Portal are amazing.
The ARB fridge freezer runs 10% of the day and draws at most 7 amps. I cannot keep the battery charged with the alternator and solar panel.
I connected the CTEK D250S to the solar panel for 3 days in full sun and it could not charge the battery over 12.4 volts. I tried 2 different batteries. I put a volt meter to solar panel and it puts out 22 volts open circuit.
I called CTEK technical support and service representative listened and answered all my questions. I am sending the unit back to CTEK for testing.
I will update this review after the unit gets tested and sent back.
Another consideration in cable selection is whether you might someday upgrade your coach battery capacity; it is possible that I might want to add a second 105 ah battery. If I did, the 20 amp charge current of the D250S would be insufficient, as modern batteries like a charge current of roughly amp-hours / 5 (check your own battery specs). For this case, CTEK makes the SmartPass supplemental unit, to attach to the D250S. The SmartPass has a charging current of 80 amps (but, it is unclear whether the 80 amps is in addition to, or in place of, the 20 amps of the D250S. When using the SmartPass, heavier cables are required. The 6mm^2 cable noted above would then become 16mm^2, which becomes 5 AWG, which, based on availability, becomes 4 AWG. I used the heavier cable so that I would not have to redo the cabling if/when I add the SmartPass.
I had a battery shop make up my cables. I had a problem with one of them, and had it redone. For a later electrical project, I got the TEMCo Hammer Lug Crimper Tool 5 Year Warranty. I wish I'd done my own cables for the D250S install. One reason is that heavy cables are more difficult to situate, especially if the terminals are not installed with the correct rotation-orientation on the cable. And, I believe that the terminals I crimped on myself are more secure and efficient than the ones I had done at the battery shop.
I've also got a 50 watt portable solar panel that seems to be working fine through the CTEK unit, though it has not been rigorously tested.
--- UPDATE ---
I have become aware that CTEK is now providing AWG cable sizes, in the manual and/or on their website. That's a nice update, so, no more searching around for conversions. In fact, CTEK's published cable sizes are all one standard AWG size smaller than the conversions I had used. With regard to the cables I had converted, above, CTEK now has 6mm^2 cable listed as 10 AWG, and 16mm^2 is listed as 6 AWG.
It's not cheap and I'm a little frustrated that they came out with a new model. I wish they had that one on Amazon when I bought this one. That's no fault of the product and again it does a great job for what's it's designed to do.