Another long post folks. Thanks for your patience with me as I work through all the options to power solution for our campers. This post focuses on how to choose between the Trimetric PWM controller and the Tracer A MPPT controller.
Here is a great site for planning solar installs. This is the wiring page -
http://www.thesolarplanner.com/steps_page9.html
Previous thread on where/how to place your charge controller:
http://www.wanderthewest.com/forum/topic/12903-solar-controller-placement/
Great site referenced in that thread on all things power related from a marine/rv perspective
RV / Marine Battery Charging - Solar & Shore Power Combined!
Post 3 in this thread links to a bunch of info on wire sizes
Is there a maximum length of wire that can be ran with a Solar Panel? - Solar Panels - Solar Panels Forum
Great info on the Victron Energy website:
GREAT paper on PWM vs MPPT -
LINK
Whitepapers -
LINK
Tech info on battery cables and a great book on the life and times of the lead acid battery -
LINK
Real life RV solar system test on Trimetric system by a guy who is a machinist extraordinaire -
LINK
His solar install (280W, Trimetric, dual Optima Platinum group31 batteries 210 AH) is really good too -
LINK
Positive review of Trimetric -
LINK
Video positive review of Trimetric -
LINK
Now, on to today’s conundrum,
How to choose between PWM and MPPT charge controllers, specifically the Trimetric SC2030 and the Tracer A Series. Both are used by folks on the forum. I’ve mentioned both in this thread. I am close to purchasing and need to make a decision. Here are my thoughts:
MPPT advantages that matter to us are:
- No need to rewire the existing 10g wire going to the roof
- No need for anything besides the usual 10g solar cables with MC4 connectors on long runs to portable panels
- Uses higher voltage/power panels that may be less expensive to purchase
PWM advantages that matter to us are:
- Usually less expensive than MPPT controllers
- Can mix panel types more readily than MPPT controllers can
MPPT disadvantages that matter to us are:
- Should not mix panels at all
- Would need two controllers for sure if mixing 24v panels on roof with lower power (*typically 12v) portable panel
PWM disadvantages that matter to us are:
- As the “need” for more power happens, we should really rewire our campers
- A long external cable will need to be home made, and HUGE to use a panel 50’ or more from the camper
Now, as the specific two controllers I am considering, here are the pros & cons:
- The cost factor is actually reversed! The Tracer A and MT50 combo is about the same price as just the TM2030 alone
- Tracer A’s charging algorithm is not as clever as the one in the Trimetric (see more in post #xxx above)
- Wiring costs are lower with the MPPT controller
- Less hassle running smaller gauge wire and no need to re-run cable with the Tracer A
- North American vs Chinese source... is that relevant?
- The Trimetric is actually better than some MPPT controllers... it is very smart for a PWM controller -
LINK
o Bogart admits freely in C1 of this
FAQ that MPPT is BETTER than PWM if you are using 24V panels
- SolarBob LOVES the SC2030. And would use the TM2030 for metering MPPT controllers too. -
LINK
- The Tracer A uses an internal shunt, so less parts cost and simpler wiring
- The Trimetric system uses an external shunt, which means it can monitor ALL charging sources and tune the solar charging using that info. Much better if your alternator is also involved in charging!
So, the crunch factors for me are:
- Trimetric is smarter
- Tracer A is cheaper and less hassle for wiring in
- Will I be using 24v panels?
- But which will charge my batteries better? And give me longer battery life?
If using 24 panels, the choice is clear – MPPT and Tracer A – by Bogarts own admission. Why? As
post #7 here says:
- A PWM controller wastes the voltage between the panels Vmp and the battery voltage. So if the Vmp of the panel is 18v and your battery is charging at 14v... The PWM controller is wasting almost 30% of the panels output.
How can I tell which panels I have or should use?
- If your panel is more than 140 watts or has more than 36 cells, then this would usually be a “high voltage” panel
- The higher cell count PV modules are cheaper per watt then the lower cell count modules - ... 12vdc modules (with 36 cells) often cost twice as much as they are being produced in lower quantities
I was thinking about the charging algorithms, and a post by xxxx got me pondering how often we actually need to use any of the smarts in these controllers. He stated in a PM to me that even after a full day of charging he sees only 93-95% of full charge. By noon he at 90%. That’s past the bulk stage, but just barely. He would be in Absorb stage only, not float. So the smarts about when to go into float stage are not applicable. This sounds like it would be normal for most FWC users, as we unlikely to have enough solar on our rigs to fully recharge daily.
IF we have enough solar power to fully charge then the advantage is to the smarter controller, the Trimetric. See this
thread, the critical point which I will quote here too:
- Finish charging (delayed boost) is different. It is an algorithm designed to limit current to the battery to no more than C/10 to prevent excessive water use and heating of the battery. And at the same time provide a high voltage finish stage that fully desulfates the negative plates. It is now almost the industry standard recommend charge profile (Trojan, US Battery, Surrette, and all industrial forklift/floor maintenance, locomotive and marine batteries). Industrial grid-powered forklift/floor maintenance and marine chargers have used it for years (IUIa with no float). Currently there are only two RE chargers that I know of that can do it - the XW from Schneider and the SC-2030 from Bogart. Of the two,
only the Bogart SC-2030 does it correctly. (emphasis added)
As I understand it, if we are NOT fully charging:
- The Trimetric will:
o Bulk charge at whatever the panels will put out until the batteries reach a voltage you can set called P1 or Bulk Volts. This is about 85% of full charge
o Then will absorb charge until it gets really hard to push current into the batteries. The current value can be set in P2. This is what most controllers (3 phase) would call “fully charged”, and would normally go into float mode. Most of us are not likely to get to this stage.
o The Trimetric goes into the fancy “finish absorb” mode that apparently
only the SC-2030 does correctly – almost all of us are not going to see this unless parked for days in the sun without a draw. However, it WILL keep your batteries very happy between camping trips!
o After an overnight draw, the Trimetric will go back into bulk mode, and repeat.
o See page 15 of Bogart Engineering instruction PDF -
Here
- The Tracer A will:
o Bulk charge at whatever the panels will put out until the batteries reach the constant voltage setpoint, much like the P1 for the Trimetric
o According to the Tracer A manual, p 5 Section
when it the controller goes into Constant Charging mode (Absorb) this controller is no longer working in MPPT mode. That’s somewhat disconcerting. Why not? It will stay in this mode for a maximum of three hours, after which it goes into float mode, whether or not the batteries are ready for it. Using xxxx’s case for example, by 2 pm the charger is going into float mode. Xxxx’s battreries where not even at 95% when the sun went down.
o Assuming the sun goes down at 7 and effective charging is possible until 5, that we are missing out on 3 hours of charging time. So even if you have enough solar to fully charge the batteries, the Tracer A won’t even try to get there.
o EPsolar manual here -
LINK
Tough decision.