PWM? Dual Battery Solar Regulator

Norman_E

Norman_E

Well-Known Member
Joined
15 Mar 2005
Messages
25,014
Location
East Sussex.
Visit site
PWM is relatively easy and cheap to implement. The very simple on/off controllers are very rarely produced these days, other than very small sized units, so it is unlikely not to be a PWM controller.

However, I suspect you are thinking of MPPT controllers which are the superior technology. If it is not labeled as MPPT it almost certainly will not have this voltage conversion incorporated. Even cheap controllers labeled as MPPT are sometimes in reality simpler PWM (non MPPT) types.

Having said that, if you have suitable 12v panels, and want a cheap controller then often a PWM (non MPPT) controller is the wise choice. Cheap MPPT controllers frequently have very poor or tracking, are not reliable, or suffer from both of these problems.

The small Victron or Genasun controllers are about the lowest cost MPPT controllers that are worth purchasing but these do not have dual battery output so additional hardware is needed if you want this function.
 
Last edited:
So far I have not spotted a dual battery MPPT controller, and I am tempted to try one of the cheap PWM ones. I think I will buy one and see how well it works. I did think of fitting a two way VSR connecting the house and start batteries and just buying a single output solar controller, but the heavy duty battery wiring is already complicated enough and connected to a dual output battery charger, so if I fit a VSR I would presumably have to connect the battery charger only to the engine battery and let the VSR take care of charging the house batteries.
 
Yes, there are very few good quality dual MPPT solar controllers. The logic is that starting the engine requires so little power that this is normally quickly replaced by the alternator. This means solar is only needed for the house bank. Splitting the solar charge between two batteries is hard to do without loosing some efficiency at least without significant cost. Most cheap dual battery solar chargers use diode isolation, loosing significant solar power in the process.

The logic above ignores the case where the boat is in winter storage. In this situation self discharge of the starting battery can be a factor. It is nice to replace this with solar. If this is the prime motivation behind fitting solar the dual solar controllers can be a sensible buy, although there are other solutions.

A simple and well proven system is to incorporate a battery switch linking, or switching the two battery banks. This is primally to start the engine with the house bank, if the start bank fails, but this same system can divert the solar charge to the start bank if this is required. However, this solution is manual system that does not help to replace the self discharge if the boat is in long term storage.
 
Last edited:
I have one of those e-bay dual controllers. It works very well for me, but I have only one solar panel so the PWM/MPPT question is not relevant to my set-up.
 
Norman_E said:
So far I have not spotted a dual battery MPPT controller, and I am tempted to try one of the cheap PWM ones. I think I will buy one and see how well it works. I did think of fitting a two way VSR connecting the house and start batteries and just buying a single output solar controller, but the heavy duty battery wiring is already complicated enough and connected to a dual output battery charger, so if I fit a VSR I would presumably have to connect the battery charger only to the engine battery and let the VSR take care of charging the house batteries.
Click to expand...

Google will find them.
 
I've had one of these https://www.sunstore.co.uk/product/ep-solar-duo-battery-solar-charge-controller-12-24v-10a/ for about 7 years and it's still going strong.

It's set to charge the starter battery first and, when that burps, turn its attention to the domestic. I fully accept that it's rare for the alternator not to get the starter battery up to snuff by the time I get out of the harbour, so solar charging is irrelevant most of the time, but it ensures the starter battery is fully charged 12 months of the year and, in extremis, while a flat domestic battery is an irritation, a flat starter could be a problem if I've run the domestic one down a bit as well.

If the controller fails, I'd certainly consider the KAL's MPPT controller, but it says it trickle charges one battery and zaps the other with full output. I'd rather have one that can switch the full output between batteries
 
I wouldn’t bother with the dual controller, really. They’re quite a bit more for what you get and if you rig a system that allows you to link your starter battery with your domestic, then if for any reason your starter battery dies, you can beef it up with help from the domestic, after which the alternator should recharge it.
 
KAL said:
I wouldn’t bother with the dual controller, really. They’re quite a bit more for what you get and if you rig a system that allows you to link your starter battery with your domestic, then if for any reason your starter battery dies, you can beef it up with help from the domestic, after which the alternator should recharge it.
Click to expand...
The whole point of a dual controller is that you can isolate the batteries from the boat systems but have the dual controller wired direct to the batteries so they carry on doing their job when you have packed up and gone home.
Sorry if I have misunderstood what you were saying.
 
LadyInBed said:
The whole point of a dual controller is that you can isolate the batteries from the boat systems but have the dual controller wired direct to the batteries so they carry on doing their job when you have packed up and gone home.
Sorry if I have misunderstood what you were saying.
Click to expand...
No problem! What I meant was that if you only have a single MPPT or PWM controller, it charges the domestic battery bank, but by rigging a switchable link to join the engine battery to the domestic bank, it would be possible to borrow power from the domestic bank to boost the starter battery if it ever ran down. I have such a system on board and it works a treat.
 
You must log in or register to reply here.

Share this page

Top