All controllers cheap or expensive have FET transistor used to control, switch off solars to avoid overcharge.
I guess, you referring FET switch controller. I wouldn't hesitate to use it.
Typically, it has basic electronic to guarantee proper function without
expensive , unnecessary electronic.
I used them a lot, early days before FETs available,
relays or contactors were used .

FETs are used everywhere, for example,
hand tools brushless motor controllers.

Select to expand quote

Charriot said..
Let me add or clarify some confusion.
..Higher voltage creates higher current..ohm law
..Wire size depends on current current only.
...24v panels charge 12v system, dropping voltage or current creates heat
regardless using passive or electronic way

some thoughts...

assuming that the amount of power is fixed, increasing the voltage reduces the current required (hence high voltage mains power lines).

and yes voltage regulation generates heat, however passive or linear circuits are relatively inefficient (wasting power by generating lots of heat), whereas a good active voltage regulator can be up to 95% efficient.

In principle you correct, but solar panels are very different power source.
eg. ....0 current - full voltage of the panel without load
0 voltage- full current of the panel
yes you can measure current availability without load, not damaging panel

It means you connect panel without controller, that's maximum power goes straight into battery. No controller need it as long as monitor voltage
and switch off panel when voltage reach 14.4V.

Select to expand quote

julesmoto said..

MysticCastle said..

julesmoto said..
So I have built a support structure to support two house size 330 watt 24 volt panels (arriving tomorrow) which will double as a Bimini. I have three batteries on board one of which which is a fair way from the panel up the front of the boat to power the anchor winch. All 3 lead acid batteries are different brands and ages. Thinking of charging the two rear ones of one panel and the front one of the other panel via 3 different cheapy charge controllers as I don't want the charge controller to stop charging once the first battery gets to full charge.
2 questions.
Firstly is there any reason why I could not use the cheap charge controllers on eBay as follows which don't seem to have any heatsink capability but claim MPPT which I believe is necessary to go from a 24 volt panel to a 12-volt battery?
www.ebay.com.au/itm/284062092832

Second question. How do I size the wire type and diameter which must travel about 11 m from the rear of the boat to near the front battery where I plan to put the third controller?
There is an existing cable that goes to that battery and it would be great if I could use the same one to avoid complex threading through bulkheads and cupboards etcetera. As this cable would now be at 24 volts from the solar panel presumably it doesn't need to be as thck as the existing one which hopefully is sized for 12 volts although I am considerably upsizing the size of the panel vs the old one (don't know what the alternator puts out but won't be using the engine enough to matter).

I would review the cheaper controllers on the basis of what input voltage they will accept. Yes MPPT operation will be also be suspect. Why voltage? My thinking is that (given the more distant location of the third battery) the solar panels in series (48 volt) running to a charge controller local to the remote battery might be an idea. The high voltage will mean lower current over this cable run and thus keep the wire gauge down. But again - the cheaper controllers may not "like" the voltage from panels in series and MPPT WILL be required. In addition non house grade solar panels are labelled not to be run in series . . . but this is not likely for house grade panels as they are run in series on a house roof. Local to the existing twin batteries you can use a second charge controller and a smart FET based switch to switch the charge from one to both batteries when the first is charged but in this case it is better for both batteries to be similar in age and capacity - maybe a third controller is the option as you suggest above - then the battery technology / capacity / age will not matter for any of the batteries. I would also recommend in all cases a charge controller with Lithium (LIFEPO) charging support - future proof the investment in the controller/s.

Thank you for this reply and all the others that people have given. Excuse my ignorance but what is an FET switch? I am kind of back to square one now because the cheap solar controllers that I ordered three of, one for each battery, turned out not to be MPPT at all despite being advertised on eBay as such. Obviously they are going back. After that experience I think I will go with Renogy or Victron at considerably more expense. When the controller is rated at a certain amperage does this mean the amperage between the solar panel and the controller or the panel and the battery? The theoretical maximum amperage is of course double between the panel and the battery as compared to the panel to controller when the battery bank is 12 volts and the panel 24 volts. Presumably however the controller knows this and as long as it is not fed in excess of it's maximum rating it knows not to exceed this rating when dishing out to the battery??
Also presumably no matter how good the controller is it can't distinguish between two different parallel connected batteries at different states of charge??

I should have been more explicit re FET switch. I referred to a means to auto isolate a start battery from the house battery. ie when the charge voltage is high the start battery is connected (for charging) and when the charge voltage drops below a threshold the start battery is isolated from the house wiring. A relay based switch can do this also.

I referred to running the panels is series to avoid heavy wire gauge going forward almost the full boat length to the winch battery - but only if there is a MPPT solar controller co-located with the winch battery. As mentioned above, ohms law kicks in. Two panels in series is approx 48volt. The current will be the same as the max current from one panel. (test by short-circuit of the panel with an appropriately rated meter). Two panels in parallel will be 24 volt and double the current than the series option - fatter wire required.

This approach does NOT work for a PCM controller - the higher voltage is wasted and not "converted" to changing power.

A true MPPT (Multi Point Power Tracking) controller will adjust the load the panels see to achieve maximum power output from the panels. The power (volts and current) required to be delivered to the battery is kind of decoupled from this - what does happen is that as the power needed to be delivered to the battery is measured, the new MPPT point of the panels is computed. So while getting the max out of the solar panels, the MPPT controller gets the best charge into the battery.

On Victron - yes a good choice but please note that if you go lithium in the future the documentation does NOT state in a very clear manner how to upgrade Victron controllers to run lithium batteries - they can be - even though the sales gumph does not mention Lithium - and I find this very strange. If you get a Bluetooth capable Victron then you can update later. If you do not get bluetooth - cheaper option today - then you will have to return it to the place of purchase (edit for re-programming) or buy the blue tooth adapter.

You can also look at iTechworld in WA. They sell a MPPT controller that is rated for 30A and up to 100volt input from the panels. I am using it on a LIFEPO house battery at present.


The options I see are:

Series or parallel or independent panels
- series means one wire run from the panels and wire sized in current rating for the short circuit rating of one panel
- parallel means double the current from the panels so either an increase in wire thickness from panels to the controller OR run the panel wires separately from the panels and place in parallel AT the controller. ie same as series wire gauge just double the wire length.
- independent means separate wires runs from each panel to separate house and winch controllers. The longer run to the winch controller will have to have increased wire thickness.

One or two or three MPPT controllers
- one, then all batteries should be the same and placed in parallel
- two, separate winch controller located in the bow and should be run from a series panel arrangement to reduce the wire size from the panel. This battery can be optimised for the winch operation now (high current). The run from the winch battery to the winch is short.
- three, overkill IMO - the cost of a third controller is better spent on matching the house batteries?

Personally I would build the two controller option with series panels. This allows lower rated wiring from the panels to the controllers (half the current of a parallel option), allows the winch battery to be sized independently to suit the heavy current required, the house batteries should be in parallel and thus be the same but do not need the heavy discharge current capability opening up other options aka Lithium in the future. I would take particular care to differentiate the >48volt wiring of the series panels however.

it's good to have some redundancy and separation between systems as well, so i vote for a second MPPT controller (or at the very least carry a spare on board)...

Select to expand quote

MysticCastle said..

julesmoto said..

MysticCastle said..

julesmoto said..
So I have built a support structure to support two house size 330 watt 24 volt panels (arriving tomorrow) which will double as a Bimini. I have three batteries on board one of which which is a fair way from the panel up the front of the boat to power the anchor winch. All 3 lead acid batteries are different brands and ages. Thinking of charging the two rear ones of one panel and the front one of the other panel via 3 different cheapy charge controllers as I don't want the charge controller to stop charging once the first battery gets to full charge.
2 questions.
Firstly is there any reason why I could not use the cheap charge controllers on eBay as follows which don't seem to have any heatsink capability but claim MPPT which I believe is necessary to go from a 24 volt panel to a 12-volt battery?
www.ebay.com.au/itm/284062092832

Second question. How do I size the wire type and diameter which must travel about 11 m from the rear of the boat to near the front battery where I plan to put the third controller?
There is an existing cable that goes to that battery and it would be great if I could use the same one to avoid complex threading through bulkheads and cupboards etcetera. As this cable would now be at 24 volts from the solar panel presumably it doesn't need to be as thck as the existing one which hopefully is sized for 12 volts although I am considerably upsizing the size of the panel vs the old one (don't know what the alternator puts out but won't be using the engine enough to matter).

I would review the cheaper controllers on the basis of what input voltage they will accept. Yes MPPT operation will be also be suspect. Why voltage? My thinking is that (given the more distant location of the third battery) the solar panels in series (48 volt) running to a charge controller local to the remote battery might be an idea. The high voltage will mean lower current over this cable run and thus keep the wire gauge down. But again - the cheaper controllers may not "like" the voltage from panels in series and MPPT WILL be required. In addition non house grade solar panels are labelled not to be run in series . . . but this is not likely for house grade panels as they are run in series on a house roof. Local to the existing twin batteries you can use a second charge controller and a smart FET based switch to switch the charge from one to both batteries when the first is charged but in this case it is better for both batteries to be similar in age and capacity - maybe a third controller is the option as you suggest above - then the battery technology / capacity / age will not matter for any of the batteries. I would also recommend in all cases a charge controller with Lithium (LIFEPO) charging support - future proof the investment in the controller/s.

Thank you for this reply and all the others that people have given. Excuse my ignorance but what is an FET switch? I am kind of back to square one now because the cheap solar controllers that I ordered three of, one for each battery, turned out not to be MPPT at all despite being advertised on eBay as such. Obviously they are going back. After that experience I think I will go with Renogy or Victron at considerably more expense. When the controller is rated at a certain amperage does this mean the amperage between the solar panel and the controller or the panel and the battery? The theoretical maximum amperage is of course double between the panel and the battery as compared to the panel to controller when the battery bank is 12 volts and the panel 24 volts. Presumably however the controller knows this and as long as it is not fed in excess of it's maximum rating it knows not to exceed this rating when dishing out to the battery??
Also presumably no matter how good the controller is it can't distinguish between two different parallel connected batteries at different states of charge??

I should have been more explicit re FET switch. I referred to a means to auto isolate a start battery from the house battery. ie when the charge voltage is high the start battery is connected (for charging) and when the charge voltage drops below a threshold the start battery is isolated from the house wiring. A relay based switch can do this also.

I referred to running the panels is series to avoid heavy wire gauge going forward almost the full boat length to the winch battery - but only if there is a MPPT solar controller co-located with the winch battery. As mentioned above, ohms law kicks in. Two panels in series is approx 48volt. The current will be the same as the max current from one panel. (test by short-circuit of the panel with an appropriately rated meter). Two panels in parallel will be 24 volt and double the current than the series option - fatter wire required.

This approach does NOT work for a PCM controller - the higher voltage is wasted and not "converted" to changing power.

A true MPPT (Multi Point Power Tracking) controller will adjust the load the panels see to achieve maximum power output from the panels. The power (volts and current) required to be delivered to the battery is kind of decoupled from this - what does happen is that as the power needed to be delivered to the battery is measured, the new MPPT point of the panels is computed. So while getting the max out of the solar panels, the MPPT controller gets the best charge into the battery.

On Victron - yes a good choice but please note that if you go lithium in the future the documentation does NOT state in a very clear manner how to upgrade Victron controllers to run lithium batteries - they can be - even though the sales gumph does not mention Lithium - and I find this very strange. If you get a Bluetooth capable Victron then you can update later. If you do not get bluetooth - cheaper option today - then you will have to return it to the place of purchase (edit for re-programming) or buy the blue tooth adapter.

You can also look at iTechworld in WA. They sell a MPPT controller that is rated for 30A and up to 100volt input from the panels. I am using it on a LIFEPO house battery at present.


The options I see are:

Series or parallel or independent panels
- series means one wire run from the panels and wire sized in current rating for the short circuit rating of one panel
- parallel means double the current from the panels so either an increase in wire thickness from panels to the controller OR run the panel wires separately from the panels and place in parallel AT the controller. ie same as series wire gauge just double the wire length.
- independent means separate wires runs from each panel to separate house and winch controllers. The longer run to the winch controller will have to have increased wire thickness.

One or two or three MPPT controllers
- one, then all batteries should be the same and placed in parallel
- two, separate winch controller located in the bow and should be run from a series panel arrangement to reduce the wire size from the panel. This battery can be optimised for the winch operation now (high current). The run from the winch battery to the winch is short.
- three, overkill IMO - the cost of a third controller is better spent on matching the house batteries?

Personally I would build the two controller option with series panels. This allows lower rated wiring from the panels to the controllers (half the current of a parallel option), allows the winch battery to be sized independently to suit the heavy current required, the house batteries should be in parallel and thus be the same but do not need the heavy discharge current capability opening up other options aka Lithium in the future. I would take particular care to differentiate the >48volt wiring of the series panels however.

Thank you very much for your detailed response. I think I will go with the series option and three different controllers as I can get controllers for about half the price of batteries and I have one new battery and two that came with the boat that are in pretty good nick. I'm thinking of the same controllers that Ramona ordered as I can get them for $95 each and they are specified as in the attached photo with maximum voltage being 100 and 20 amps. I assume the 20 amps won't be a problem with a 660 Watt (series) system at 48 volts (660w divided by 48v=14A approx). Of course if all the power were directed to one controller then 20 amps would be exceeded (660w divided by 12v=55 A) charging a 12 volt battery. However as 3 batteries will be involved and as presumably each controller is smart I assume that it will never try to divert more amperage than it is rated at towards one battery only. I wonder if you would mind confirming my understanding as above based on the specifications in the attached pictures using one controller for each battery and 2 panels in series (the one pair of combined 2 panel series output wires split into three pairs each going to one controller although one controller being significantly further away from the panels than the other 2). Thanks again heaps

Hi Jules,
So, it sounds like you are going to wire your 2x330w solar panels in series and have 3 MPPT controllers in parallel each charging a different battery.

My only concern is the paralleling of those three chargers across the same input source. Each charger is expecting all the the available input power and is going to tune it's parameters accordingly to utilize that input for max output. No idea how the three controllers are going to interfere/cooperate with one another. My gut feeling is that it will depend on the condition of the batteries, each charger will sense the battery condition and determine the charging mode it needs to operate in. If all three are going into bulk then the power draw from one charger may make it difficult for the other chargers to set their parameters, or they may just share the available load and as each draws less there is more available for the others.

guess there is only one way to find out, good luck with your installation.

community.victronenergy.com/questions/59817/single-pv-with-2-x-mppts.html

Select to expand quote

DrogueOne said..
Hi Jules,
So, it sounds like you are going to wire your 2x330w solar panels in series and have 3 MPPT controllers in parallel each charging a different battery.

My only concern is the paralleling of those three chargers across the same input source. Each charger is expecting all the the available input power and is going to tune it's parameters accordingly to utilize that input for max output. No idea how the three controllers are going to interfere/cooperate with one another. My gut feeling is that it will depend on the condition of the batteries, each charger will sense the battery condition and determine the charging mode it needs to operate in. If all three are going into bulk then the power draw from one charger may make it difficult for the other chargers to set their parameters, or they may just share the available load and as each draws less there is more available for the others.

guess there is only one way to find out, good luck with your installation.

community.victronenergy.com/questions/59817/single-pv-with-2-x-mppts.html

Yes I am a bit worried about that thank you. It's a toss up between using a series set up vs getting a thicker cable and devoting one entire paralleled panel to the battery in the bow for the anchor which doesn't get used much use anyway

Select to expand quote

julesmoto said..

DrogueOne said..
Hi Jules,
So, it sounds like you are going to wire your 2x330w solar panels in series and have 3 MPPT controllers in parallel each charging a different battery.

My only concern is the paralleling of those three chargers across the same input source. Each charger is expecting all the the available input power and is going to tune it's parameters accordingly to utilize that input for max output. No idea how the three controllers are going to interfere/cooperate with one another. My gut feeling is that it will depend on the condition of the batteries, each charger will sense the battery condition and determine the charging mode it needs to operate in. If all three are going into bulk then the power draw from one charger may make it difficult for the other chargers to set their parameters, or they may just share the available load and as each draws less there is more available for the others.

guess there is only one way to find out, good luck with your installation.

community.victronenergy.com/questions/59817/single-pv-with-2-x-mppts.html

Yes I am a bit worried about that thank you. It's a toss up between using a series set up vs getting a thicker cable and devoting one entire paralleled panel to the battery in the bow for the anchor which doesn't get used much use anyway

Apologies. After more reading, my past advice was bad and using three controllers will exacerbate the issue further as mentioned by DrogueOne above. One MPPT controller per set of panels is best. Then each controller will be able to control the load presented to the panel without being interfered with by the other controllers.

Select to expand quote

MysticCastle said..

julesmoto said..

DrogueOne said..
Hi Jules,
So, it sounds like you are going to wire your 2x330w solar panels in series and have 3 MPPT controllers in parallel each charging a different battery.

My only concern is the paralleling of those three chargers across the same input source. Each charger is expecting all the the available input power and is going to tune it's parameters accordingly to utilize that input for max output. No idea how the three controllers are going to interfere/cooperate with one another. My gut feeling is that it will depend on the condition of the batteries, each charger will sense the battery condition and determine the charging mode it needs to operate in. If all three are going into bulk then the power draw from one charger may make it difficult for the other chargers to set their parameters, or they may just share the available load and as each draws less there is more available for the others.

guess there is only one way to find out, good luck with your installation.

community.victronenergy.com/questions/59817/single-pv-with-2-x-mppts.html

Yes I am a bit worried about that thank you. It's a toss up between using a series set up vs getting a thicker cable and devoting one entire paralleled panel to the battery in the bow for the anchor which doesn't get used much use anyway

Apologies. After more reading, my past advice was bad and using three controllers will exacerbate the issue further as mentioned by DrogueOne above. One MPPT controller per set of panels is best. Then each controller will be able to control the load presented to the panel without being interfered with by the other controllers.

Thank you, looks like back to 24 volts and one controller per panel and matched batteries on the controller feeding the start and house battery at the rear. Got my first Renogy Rover controller (thanks for the recommendation Ramona) yesterday which looks like a very nice piece of kit at a very reasonable price and also finally got my two 330 kW panels mounted on the boat after mounting them on my car roof racks and transporting them for 2 hours at 95 kph on an Expressway in the slow lane with hazard flashers going and trucks passing me for fear of them lifting off. Made my car look like a solar vehicle:-). I thought they might look disproportionately large on the boat but they look fine on my ns38 despite being full size house panels and should provide a good bit of shade too :).

I use a VSR to charge my aux battery.
When the house batteries reach 13.8 v, the VSR closes and allows the solar, wind or motor to charge the aux battery. At that point all batteries are connected and will remain connected untill the voltage in the system falls below 12.8v and then the aux battery will disconnect from the house batteries.
The aux battery is wired into the system and can be used for powering everything . Aux is an optima yellow top 75 A/hr 900cca.

After we solve the first hurdle get some solar energy and stored, we find out
If our demands is covered.
In my case, I switch off thirsty fridge / 1.2 kW over 24 hours/ ,
and what happens next.
Simple answer, controller/ s take care of it. Yes or No.
My system is 2 set of sollars , 2 controllers, one set of batteries.
Last 2 weeks when all load is off my bat. voltage is 14.4V
Never less, I am not convinced it's any good for battery.
Believe, 2 controllers chasing each other.
I implemented switches, I leave both systems ON only in case of large demands.

julesmoto
now you post nameplate of your panels, great.
I just sold 8 of these and did some testing before. Installed 6.6 kW instead.

considering your panels 9.7A ideal lab conditions, available current would be around 8Amps. In this case One controller two panels parallel.......ideal.