The CTEK D250 Dual is a 12 volt 20 amp DC to DC Charger integrating a high efficiency MPPT Solar regulator.  It also functions as an automatic battery isolator.
So why do we need a DC to DC charger? After all, our vehicles alternator will charge our second battery… won’t it?
Manufacturers of modern vehicles are required to meet certain targets with regards to pollution, fuel economy and efficiency (EURO 5 for example). As a result, vehicle alternators are now very clever devices, controlled by the vehicles engine computer. Now the alternator and its control systems are designed to do its task with best efficiency… that is, run the vehicles electrical systems.  IT WAS NEVER DESIGNED TO CORRECTLY CHARGE AN AUXILIARY DEEP CYCLE BATTERY!!!
The maths are relatively simple. Modern alternator output voltages are not nearly high enough for effective charging (typically just 13.2 to 13.4 volts), but we need 14.4 to 14.6 volt to charge most cyclic batteries.
A DC to DC charger solves this problem by ‘boosting’ the low alternator volts to a more suitable voltage for fast, safe and efficient charging. This results in longer battery life and better performance.
The D250 Dual also have a ‘multi power point tracking’ (MPPT) Solar regulator built in which can, depending on the installation, charge the battery with both alternator and solar at the same time.


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