PWM vs MPPT charge controller for solar

[Silma]

Hello,

 

So I have read a lot on forums about how PWM and MPPT charge controllers work and their pros and cons. There seems to be a lot of disagreement whether a MPPT controller is worth the extra money for systems in the 200-500W range. This is where my chosen panels lie. My system is:

 

3 x 100W panels each at

Vmax = 18.75V

Voc = 22.09V

Imp = 5.33A

feeding 3 x 110ah leisure batteries

 

So what I am asking is has anyone got any experience/advice on each type of charge controller and is an MPPT worth the extra money?

 

I guess I should also say that the boat is a live aboard mostly in and around London.

 

Thanks in advance

[trackman]

I'd say as you live aboard an MPPT would repay the extra cost. Not only should it give better results in favourable conditions, it should give worthwhile inputs to the batteries for longer when conditions are less than optimal.

[MtB]

I have one of each and I far prefer the MPPT.

 

Main reason to get an MPPT in my opinion is for all the data reporting you get on the LCD, stuff like battery voltage, panel voltage, charge state, charging current etc. None of this available on my PWM controller.

 

M

MtB

[FidoDido]

The PWM controller Bimble sell for 35 quid has all that info. I used one for a few weeks. It's a good bit of kit, but not suited to the panel I have, which is a 36v one.

 

I would say that if you panels were producing a higher voltage, then MPPT would definitely be the way to go. However, with those panels, I would think the actual power difference between PWM and mppt would be fairly small.. Perhaps 10-15%.

 

If that extra 10% is worth another 70 quid, it's for you to decide.

 

Or, get a 250w house panel (higher voltage), and a mppt.. Might work out cheaper.

[Justme]

However, with those panels, I would think the actual power difference between PWM and mppt would be fairly small.. Perhaps 10-15%.

 

 

Unless you wire them in series....

 

That will lower the current in the array cables so they can be longer & thinner for less losses.

[DeanS]

I have 2 x 230watt panels in series, wired to a 30Amp MPPT. On sunny days it supplies almost the full 30Amps. (if the batteries need it)

 

eta. Be careful of the cheap MPPTs...from China..apparently they arent the real thing. I think the one I have is from Bimble Solar.....

Edited September 26, 2013 by DeanS

[MtB]

 

eta. Be careful of the cheap MPPTs...from China..apparently they arent the real thing.

 

That's an interesting point. There is no way I'd be able to tell the difference between a real MPPT and an MPPT box with cheaper PWM guts inside, if the LCD display was there (as others have said exists)!

 

MtB

[peterboat]

All true I have a mppt tracer and it does the stuff I want batteries are well charged (1500 amp hours) by lunch on a sunny day my old panels with mpw worked ok but could never produce the same amount of power you pay your money etc........

 

Peter

[Silma]

Great, thank you for the replies.

 

You guys have convinced me that a MPPT is the way to go and will be worth the extra money.

 

So the follow up question is can you recommend and controllers/makers?

 

Some quick calculations with my panels wired in series

Voc = 22.09 * 3 = 66.27V

Stepped down to 14.5V would give

Imp = 24.36A

 

So I need a 30A controller that can handle 300W max PV input.

 

There is one on Bimble Solar that seems to fit the bill and it has good reviews on Amazon. It is a cheap chinese one though...

http://www.bimblesolar.com/offgrid/mppt/30amppt

[DeanS]

 

There is one on Bimble Solar that seems to fit the bill and it has good reviews on Amazon. It is a cheap chinese one though...

http://www.bimblesolar.com/offgrid/mppt/30amppt

 

Thats the one I have ( I have 2 actually), and they work great. I dont know what "indications" they provide as I just connected the wires and measure output using a clamp meter. It's putting out 16A right now, in a weakish winter sun) eta...with 460Watts of panels. On brighter days it has been up to almost max.

Edited September 27, 2013 by DeanS

[matty40s]

Great, thank you for the replies.

 

You guys have convinced me that a MPPT is the way to go and will be worth the extra money.

 

So the follow up question is can you recommend and controllers/makers?

 

Some quick calculations with my panels wired in series

Voc = 22.09 * 3 = 66.27V

Stepped down to 14.5V would give

Imp = 24.36A

 

So I need a 30A controller that can handle 300W max PV input.

 

There is one on Bimble Solar that seems to fit the bill and it has good reviews on Amazon. It is a cheap chinese one though...

http://www.bimblesolar.com/offgrid/mppt/30amppt

I have fitted many of these, and use one myself. No reported faults in 2 years and they do what it says it should do.

[smileypete]

Great, thank you for the replies.

 

You guys have convinced me that a MPPT is the way to go and will be worth the extra money.

 

So the follow up question is can you recommend and controllers/makers?

 

Some quick calculations with my panels wired in series

Voc = 22.09 * 3 = 66.27V

Stepped down to 14.5V would give

Imp = 24.36A

 

So I need a 30A controller that can handle 300W max PV input.

 

There is one on Bimble Solar that seems to fit the bill and it has good reviews on Amazon. It is a cheap chinese one though...

http://www.bimblesolar.com/offgrid/mppt/30amppt

 

You need to use Vmp not Voc

 

A 20A should more or less scrape by, but a 30A will a bit of room for later expansion.

 

cheers, Pete.

~smpt~

Edited September 27, 2013 by smileypete

[Justme]

 

You need to use Vmp not Voc

 

 

 

 

No you dont. Well not when speccing the controller max input voltage.

 

You need the VOC & you need to add the temperature coefficient as well for the worst / lowest temps you expect to get.

 

Going over voltage can & does kill controllers very quickly.

 

The controller will see the VOC at certain points in the charge cycle.

 

When speccing the output amps then yes you do need the Vmp.

Edited September 27, 2013 by Justme

[smileypete]

 

 

No you dont. Well not when speccing the controller max input voltage.

 

You need the VOC & you need to add the temperature coefficient as well for the worst / lowest temps you expect to get.

 

Going over voltage can & does kill controllers very quickly.

 

The controller will see the VOC at certain points in the charge cycle.

 

When speccing the output amps then yes you do need the Vmp.

 

You need to read my post more again, more carefully this time and pay attention to post I quoted.

 

Read post 9 carefully and tell me what you think

 

cheers, Pete.~

smpt~

[Silma]

Even if I went by Vmp it would still be over 20A (20.68A). My understanding is that panels can produce over the Vmp due to temperature and edge of cloud effect. So a safety factor is always needed.

 

But we are all agreed that a 30A controller is needed.

The controller on bimble can handle 150V output from the panels so my max of 67V is well within the limit.

 

Thanks very much for the help, it is much appreciated

[George94]

 

Thats the one I have ( I have 2 actually), and they work great. I dont know what "indications" they provide as I just connected the wires and measure output using a clamp meter. It's putting out 16A right now, in a weakish winter sun) eta...with 460Watts of panels. On brighter days it has been up to almost max.

 

So you have two controllers wired in parallel to the batteries, and separately to two panels (or banks of panels)?

[peterboat]

 

So you have two controllers wired in parallel to the batteries, and separately to two panels (or banks of panels)?

Yes I do as well and have no problems with them (or none that I know of)

 

Peter

[George94]

Yes I do as well and have no problems with them (or none that I know of)

 

Peter

 

Sounds good. Makes increasing the number of panels easier if you just have to add another MPPT, rather than swap out the old one.

[Justme]

 

You need to read my post more again, more carefully this time and pay attention to post I quoted.

 

Read post 9 carefully and tell me what you think

 

cheers, Pete.~

smpt~

And you need to read mine too.

 

I was explaining that just using Vmp is not the only thing you need to consider to spec the controller as you need the maximum voltage that the controller will see or you could blow it up.

[smileypete]

Even if I went by Vmp it would still be over 20A (20.68A). My understanding is that panels can produce over the Vmp due to temperature and edge of cloud effect. So a safety factor is always needed.

 

But we are all agreed that a 30A controller is needed.

The controller on bimble can handle 150V output from the panels so my max of 67V is well within the limit.

 

Thanks very much for the help, it is much appreciated

 

The Tracer MPPTs should limit itself to the max current, even if more power is available.

 

If there's NO space for adding more panels later on and money is tight then using a cheaper 20A Tracer is an alternative.

 

Sure there will be times when it's not making use of all the available power but it won't be that often.

 

cheers, Pete.

~smpt~