MPPT vs PWM - The Solar Controller Test!

[wildebus]

It could just about cope with the fridge kicking in, but sounded heavily loaded. That said it runs for about 6 hours on very little fuel so good for emergencies.
Finally I returned home to find Murky's leisure batteries fully charged, funny what a little sun will do.
This morning I switched on the inverter and fired up 2 of the 7.5 amp chargers to bring up the engine start batteries.
20 amps drain from the two chargers, not the most efficient.

This one of the down side of the bigger mercs, their is a current drain I've never been able to track down. They provide an isolation switch for the batteries, but then the alarm or powered doors don't work. Odd characteristics, it draws more current in winter than it does in summer. Also when connecting the supply there is a current serge just like a big capacitor is in the circuit somewhere?

A generator certainly is a handy thing to have if the need demands it.
You don't have an engine preheater do you? I had one in my VW T5 that apparently kicked on under 10c. Went wrong and something in it ran all the time even with ignition off. Not good for the battery that was for sure!

In my VW LT (like a Sprinter Mk1), I have the tacho constantly going which is no doubt some kind of draw. That plus the door step lights that are on whenever the doors are open (so if I leave the slider open, the starter battery is getting used).
As it happens I am just prepping for another test on this area I've disconnected the bi-directional Cyrix-CT VSR and am keeping an eye on how the Starter Battery voltage is decaying.

A very smooth decline there (the Battery is new since around July this year and is a fairly nice unit). because it is so smooth it is possible to clearly specific events but there is certainly a constant power draw visible.

In the next day or so I will be fitting a prototype programmable Starter battery trickle charger (similar to a Battery Master, but with more features and capability) to see how that manages the starter.

 

[wildebus]

Personally, if your thinking about a charger just for storage I'd be tempted by one of those smaller Victron ones. Say around 15amps. It's not like you'll be charging in a hurry to go somewhere. Once it's done it's business it goes into storage more.

The little Victron IP65 units are very handy. They are pretty weatherproof and come with quick-disconnect plugs which makes them easy to move around if you have a 'fleet' of vehicles you may want to use a charger on (it is not a bad idea at all to get a proper charger on once a month on a car, as the alternator never does a full charge). CTEK do chargers with similar features and are very good as well, but I like the extended warranty on the Victron (5 years vs 3 years) and the bluetooth monitoring you get for around the same price.

 

[Yang07]

Understanding what an MPPT or PWM solar charge controller does will help operate your RV appliances with clean, free, and efficient energy: An MPPT controller automatically adjusts the solar panels’ output voltage to recharge the deep cycle batteries. A PWM controller typically waits for the system voltage to stabilize and fall naturally before initiating the absorb charging state. I can say that the MPPT’s four-stage charging mechanism is better, safer, and healthier for your RV’s deep cycle batteries than a PWM’s three-stage design. A PWM charge controller is ideal for small-scale solar projects, generating less than 2,000 watts. The controller can accommodate up to 60 amperes and run on 12 and 24-volt systems. A MPPT is perfect for solar power systems that generate more than 2,000 watts. It can handle up to 100 amperes and operate on 36 and 48 volt systems.

 

[Nabsim]

PWM controllers are preferred for large solar farms so not just small scale stuff. On motorhomes in U.K. mppt will usually be the best option

 

[Yang07]

Understanding what an MPPT or PWM solar charge controller does will help operate your RV appliances with clean, free, and efficient energy: An MPPT controller automatically adjusts the solar panels’ output voltage to recharge the deep cycle batteries. A PWM controller typically waits for the system voltage to stabilize and fall naturally before initiating the absorb charging state. I can say that the MPPT’s four-stage charging mechanism is better, safer, and healthier for your RV’s deep cycle batteries than a PWM’s three-stage design. A PWM charge controller is ideal for small-scale solar projects, generating less than 2,000 watts. The controller can accommodate up to 60 amperes and run on 12 and 24-volt systems. A MPPT is perfect for solar power systems that generate more than 2,000 watts. It can handle up to 100 amperes and operate on 36 and 48 volt systems.

In general, MPPT charge controllers are more expensive than PWM ones, though they’re also more efficient.