Upgrading Zamp ZS-30 controller

[Calson]

I would like to upgrade the Zamp PWM charge controller with a more efficient MPPT one but still have the device or a display in the current location of the Zamp. Has anyone done this?

 

[Old Navy-WO]

I would like to upgrade the Zamp PWM charge controller with a more efficient MPPT one but still have the device or a display in the current location of the Zamp. Has anyone done this?

EPEVER gets pretty good reviews and has an optional remote display.

Victron makes a remote for their MPPT charge controller.



On small systems typical of RVs, many people have done real world testing of PWM vs MPPT and found no significant advantage. On larger 24/48v systems, MPPT is a clear winner.

 

[Calson]

The MPPT charge controllers are 30% more efficient and it is best to wire solar panels in series and get 24V with two panels or 48V with four panels. The higher the voltage the less the current loss with any gauge or length of electrical cables.

 

[AJMike]

On small systems typical of RVs, many people have done real world testing of PWM vs MPPT and found no significant advantage. On larger 24/48v systems, MPPT is a clear winner.

Before I comment I want to clearly state that I know very little about PWM and MPPT solar controllers, and anything I post may well need some correction. However as a curious kind of guy and so did some reading on the differences and found a very interesting article which contained a flow chart to determine what kind of controller the user might need.

The thrust of the article was that for small systems, like those in RVs, there was little difference between the efficiency of the two systems, and that PWM controllers became more efficient as the temperature increased so that users like myself who live in the warmer states (Arizona here) probably get about the same, if not more, efficiency from a PWM as an MPPT.

Here is the flowchart.

 

[DavidEM]

I see the chart but I will reserve my belief until I see the physics behind it. In other words, seeing a chart doesn't make it so.

David

 

[AJMike]

I see the chart but I will reserve my belief until I see the physics behind it. In other words, seeing a chart doesn't make it so.

David

As I said at the start of my post, I know little to nothing about all of this, however if the post itself will help you can find it here.

https://www.solar4rvs.com.au/buying/buyer-guides/choosing-the-right-solar-charge-controller-regulat/

I posted the flow chart because it is simpler and more condensed but you can read the tech stuff at the link.

 

[DavidEM]

Thanks for the link. Here is the gist of the physics excerpted from the article. Maybe most can understand it, particularly the 17-25% improvement (noted below in bold) in battery charging power with an MPPT controller vs a PWM:

With a PWM controller the power drawn from the panel is 5.2A * 13V = 67.6 watts. This amount of power will be drawn regardless of the temperature of the panel, provided that the panel voltage remains above the battery voltage.

With an MPPT controller the power from the panel is 5.0A * 18V = 90 watts, i.e. 25% higher. However this is overly optimistic as the voltage drops as temperature increases; so assuming the panel temperature rises to say 30°C above the standard test conditions (STC) temperature of 25°C and the voltage drops by 4% for every 10°C, i.e. total of 12% then the power drawn by the MPPT will be 5A * 15.84V = 79.2W i.e. 17.2% more power than the PWM controller.

In summary there is an increase in energy harvesting with the MPPT controllers, but the percentage increase in harvesting varies significantly over the course of a day.

 

[AJMike]

Thanks for the link. This is the gist of the physics and maybe most can understand it, particularly the 17-25% improvement in battery charging power with an MPPT controller vs a PWM:

With a PWM controller the power drawn from the panel is 5.2A * 13V = 67.6 watts. This amount of power will be drawn regardless of the temperature of the panel, provided that the panel voltage remains above the battery voltage.

With an MPPT controller the power from the panel is 5.0A * 18V = 90 watts, i.e. 25% higher. However this is overly optimistic as the voltage drops as temperature increases; so assuming the panel temperature rises to say 30°C above the standard test conditions (STC) temperature of 25°C and the voltage drops by 4% for every 10°C, i.e. total of 12% then the power drawn by the MPPT will be 5A * 15.84V = 79.2W i.e. 17.2% more power than the PWM controller.

In summary there is an increase in energy harvesting with the MPPT controllers, but the percentage increase in harvesting varies significantly over the course of a day.

Yes. I understood the post.

I also understood that any difference in efficiency on small systems, like the one on my RV, and at lower voltages, again like the one on my RV, is very small and hence perhaps not worth the cost of the MPPT solar controller.

I also understood the 4% drop in MPPT efficiency per 10C over the baseline and given that the solar panels here in southern Arizona get so hot that they actually burn your hands in the summer the efficiency drop is probably somewhere around 12-16%, perhaps higher. Given the original 17% difference any gain for MPPT probably completely disappears.

The point is that the performance difference is small enough, even when it exists, to not be worth the cost for me.

 

[DavidEM]

I don't understand why he quoted that the efficiency drop with hot solar panels applies only to MPPT controllers. It affects both Imp as well as the current output below Imp similarly. It is just like having a smaller panel as they get hot. So I don't buy his stated reduction from 25% to 17%.

Is 25% or even 17% worth it to you? Maybe not if you have lots of room for panels and aren't trying to squeeze the last watt of power out of them. With panels costing about $1 per watt, if you have the room, just add another panel and use a PWM controller. A Victron MPPT controller suitable for 4 100 watt panels costs about $200. Can you buy a quality PWM controller for $100 less?

David

 

[AJMike]

I don't understand why he quoted that the efficiency drop with hot solar panels applies only to MPPT controllers. It affects both Imp as well as the current output below Imp similarly. It is just like having a smaller panel as they get hot. So I don't buy his stated reduction from 25% to 17%.

I suppose it is because of these statements:

With a PWM controller the current is drawn out of the panel at just above the battery voltage, whereas

With an MPPT controller the current is drawn out of the panel at the panel “maximum power voltage” (think of an MPPT controller as being a “smart DC-DC converter”)

If the MPPT controller draws the current at the "maximum power voltage" and if the output voltage of the panel drops as it gets hot, then the current output will drop as well.

If the PWM controller draws the current just above the battery voltage, then it is not affected by the drop in panel output.

Is 25% or even 17% worth it to you? Maybe not if you have lots of room for panels and aren't trying to squeeze the last watt of power out of them. With panels costing about $1 per watt, if you have the room, just add another panel and use a PWM controller. A Victron MPPT controller suitable for 4 100 watt panels costs about $200. Can you buy a quality PWM controller for $100 less?

Everyone's needs are different so I can only talk about mine, although there are probably a lot of others with similar, if not identical, needs and concerns.

Our RV is small, a 24 foot Class C RV with limited landscape on the roof. Much of that landscape is taken up with the AC, the ceiling fan cap, the bathroom vent, the bathroom skylight dome, the radio roof antenna, the solar cap and the 3 existing solar panels. I am planning to add a 4th panel so I did some analysis of what panels fit into the jumble of space available, and there is precious little. The RV came with 2 flexible solar panels (by SunPower, which are actually dandy panels and produce quite a bit of output) and I added a 3rd shortly after buying the RV. I have room for at most 2 more 100 watt flexible panels or 1 100 watt rigid panel, so I have to mostly make do within those limits.

That would seem to argue that I should get as efficient a solar controller as I could find, but in reality the 3 existing solar panels pretty much do what we need and a 4th and/or 5th will probably give us everything we use during the day. Given that there seems to be little reason to spend the money to upgrade the solar controller to an MPPT. For what purpose? Given how hot it can get here in southern Arizona any additional output from an MPPT controller, even if it exists, would be really minor and, in my view, not worth the additional cost.

Your question - Can you buy a quality PWM controller for $100 less? - has no bearing because I won't need a new solar controller. The existing 30 amp Zamp controller will do just fine, and I have better places to spend the money.

Of course YMMV.

 

[Calson]

I did a great deal of research before installing a solar system on my camper in 2014 and again when I added a PV array to the roof of my house a year later. Not much has changed except that the cost for most panels has gone down over the years, although the Zamp panels are grossly overpriced.

Panels provide the best performance with a temperature range and if they get too hot then the output decreases. It is why panels are raised off a roof as much as is practical to allow for airflow underneath them.

With my RV and its 10 cu ft compressor fridge the two 100W panels are enough to keep the fridge at temperatures for food but they is precious little extra to use to run anything else. I could rely on running the generator or driving down the highway to recharge the house batteries or I can add more solar panels. Based on my own experience adding more panels makes more sense as I avoid staying in RV parks.

A Vicron MPPT controller costs $100 more than a comparable Zamp PWM controller and so the people at Winnebago decided to go with the cheaper ccntroller and pocket the savings for themselves. I expect this from an American company. It is also why there are thousands of companies selling aftermarket products to owners who wish to upgrade their vehicle.

I wanted to avoid routing the wiring for solar as that is what took me 75% of my time with the last RV installation. So having to add or replace the roof panels and replacing the charge controller is part of the cost of owning the RV and wanting to dry camp as much as possible.

Spending $300 to have 30% more charge going to the house batteries by replacing the charge controller is well worth the cost to me. Others may not care about what they get from their solar panels or how long they can go off the grid without problems. Others may also have a fridge that runs off propane and so the house batteries take far less of a hit.

I phoned 6 RV solar installers last week and they were booked up through February of next year. Obviously there are a great many RV owners who want to add or upgrade solar.

 

[AJMike]

Not much has changed except that the cost for most panels has gone down over the years, although the Zamp panels are grossly overpriced.

My Fuse came with 2 100 watt SunPower flexible panels and you can buy those on Amazon for $195 each. If you go to the Zamp website you can find the same panel with a plug converter for the Zamp roof top combiner for $644.44. Same panel, only with the connector conversion for Zamp.

It is listed as a kit on the Zamp site, but if you read the details you see that it is only the panel and the plug conversion.