Question about Will's milk crate build.

[Chromdome35]

I see that Will used an AC to DC converter to charge the battery via a wall outlet.

What I'm confused about is since the input isn't coming through any type of charge controller, how does the charger know when the battery is full? He said on his first build he shouldn't have hooked the AC/DC Converter to the MPPT Controller, why?

I'm a total newbie to all this, can someone explain for me?

 

[bkch0]

With raw cells, the battery itself will take in less and less current once it fills up. The charge controller has a pre-programmed threshold. Once this threshold is reached, the charge controller stops charging the battery.

If the battery has a BMS, the BMS may kick in first (if it has a higher threshold) and stop charging before the charge controller.

 

[bkch0]

An AC/DC charger is typically hooked up directly to the battery to charge it. In his video, if he did this, he can only charge the battery with 14v, 10A.

However, if he sets the AC/DC charger to 24v+, 10A and have it go into the MPPT controllers PV inputs (in this case, the AC/DC charger is acting like a solar panel)... The MPPT controller can convert that to 14v, 15A+, thus charging the battery faster.

All this is ok until he added the solar panels to the MPPT controller. Both the solar panel wires and the AC/DC charger wires were screwed into the PV inputs of the MPPT controller. If his solar panels has a significant higher voltage than his AC/DC charger, it *may* damage the AC/DC charger.

In order to correct this, he was going to connect the AC/DC negative to the battery but the battery's negative terminal already has too much stuff on it so he decided to connect it to the MPPT battery output screw terminal. With this method, he explains that the wire gauge is sufficient to allow this method.

 

[mikefitz]

how does the charger know when the battery is full?

Using an AC to DC unit to charge a battery directly is not a good idea, since the DC unit will not know when the battery is fully charged and continue charging, perhaps overcharging and damaging the battery. An AC to DC battery charger would detect that the battery was full and either stop charging or drop to a float maintaining value.

said on his first build he shouldn't have hooked the AC/DC Converter to the MPPT Controller, why?

This is also not a good idea, the MPPT controller is designed to work with a current limited source, the solar panel. Feeding the MPPT controller with a badly designed DC power supply may/will cause the power supply output to become unstable and may cause internal failure.

A number of the type of AC to DC units used in the video have been found to unreliable.

In my view the videos should be regarded as entertainment and an introduction the batteries and charging. They are not necessarily best engineering practice.


Mike

 

[Chromdome35]

Thanks for the responses guys!

One follow-up question, Instead of using the AC to DC converter to charge the battery, why wouldn't a dedicated battery charger like a Battery Tender or a NOCO be a better choice? The only thing I can think of would be charging speed?