mppt charge controller versus my alternator

System · May 2007

hello All!
I've just purchaced a Kyocera 130 and a bluesky mppt 25 amp charge controller, which I plan to attach to my RV. My question is what happens while I've got my engine running? I can seperate my engine battery from my house batteries, but I would like to run my fridge and stereo and charge my house batteries off the alternator when I'm underway.
Will I have to dissconnect the charge controller and panels while charging the house batteries from the alternator?

It would be great if the panels could assist my alternator while underway, possibly increasing my fuel economy(however slightly), but not at the cost of my charge controller.

Any info by those in the know would be appreciated

jauguston · May 2007

Re: mppt charge controller versus my alternator

I just did the same thing with two 130w Kyocera's and the SB2000E and they work fine hooked up permanently, not switched off while traveling.

Jim

crewzer · May 2007

Re: mppt charge controller versus my alternator

Landyacht318,

The system will work. How well is another issue.

The typical absorption voltage for an RV house battery is ~14.4 V to ~14.8 V. Few automotive alternators/regulators deliver this voltage level as measured at the battery terminals. The result is that the combination of the alternator and the PV controller will typically partially charge the house battery, but not fully.

On option is to partially recharge the house battery from the alternator and PV system, and then finish the charge with the PV system alone. I sort of used this approach with my old camper, and it worked well. All “underway” camper loads were powered from the alternator.

Another approach is to consider a three-stage alternator regulator. See: http://www.balmar.net/

Finally, the MPPT controller will likely not offer any performance boost to your relatively small system. A PWM controller such as the Morningstar SunSaver -10 or the ProStar 15 would work just fine with your 130 W (STC) PV module.

HTH,
Jim / crewzer

jauguston · May 2007

Re: mppt charge controller versus my alternator

Just to add to what Jim said I am seeing a 15 - 20% amperage increase through the SB2000E so for my setup it seems well worth it to have the MPPT. I saw the same gain when I had one panel. I am new to all this and don't know what features the other controller mentioned has but I really like being able to read the amperage output both into and out of the controller and the output voltage on the controller panel meter. I have a existing permenant mounted digital volt meter in line with my battery bank and it and the SB2000E agree on voltage to within .01v.

Jim

System2 · May 2007

Re: mppt charge controller versus my alternator

Thanks for the info.
My main concern was that my "120" amp alternator which is regulated within the engine computer would some how harm or be harmed by the mppt charge controller. After once burning out my alternator deep in Baja(no solar array), I've become very anal about my battery voltage and capacity. I will not even try to charge the house batteries with the alternator if they drop below 12.2 volts.When charging my three batteries the lowest voltage my digital voltmeter reads is 14.4. I've never checked the amps.
I was wondering if the sb2000e displays the amperage incoming from the alternator even though it is not wired inbetween the alternator and battery bank. I would think the charge controller would get very confused with so much juice beng pumped in from another source. I know that most automotive alternators really are only designed top top off only partly discharged starting batteries, and can never really top off a 50% dod deep cycle battery bank
Geoff

crewzer · May 2007

Re: mppt charge controller versus my alternator

I am seeing a 15 - 20% amperage increase through the SB2000E so for my setup it seems well worth it to have the MPPT.

That's great! I'd be interesting in knowing more about the circumstances of the described increase. I've seen up to a 30% current boost in my system, but it typically happens in the morning when the batteries are low, the PV array is cold, and charge current is low. So, although there's a nice instantaneous current boost, it doesn't translate into much additional energy. Once the batteries charge up a bit, the array gets hot and the MPP voltage drops -- especially in the late spring, summer and early fall -- there's little net energy boost.

The issue isn't how much current boost. Instead, it's how much energy boost (Ah or Wh) in a day.

Don't misunderstand: I like MPPT technology, and my controller is an MPPT type. But, when you factor in the marginal cost over a PWM controller, the fact that MPPT typically offers little or no performance boost in the absorb or float stages (both are current limit operations), that their tare loss offsets part of their gain, and that there's typically little "extra" voltage available from hot PV modules during typical RV'ing weather to convert to extra current in the bulk stage, my conclusion is that MPPT technology is a hard sell for "small" arrays, say, 300 W to 400 W or smaller.

But, for those that have 'em and like 'em, enjoy!

Regards,
Jim / crewzer

crewzer · May 2007

Re: mppt charge controller versus my alternator

I was wondering if the sb2000e displays the amperage incoming from the alternator even though it is not wired in between the alternator and battery bank.

Nope... the meter displays battery voltage, current from the PV array to the controller, or current from the controller to the battery circuit, all user selectable via a front-panel three-way switch.

HTH,
Jim / crewzer

jauguston · May 2007

Re: mppt charge controller versus my alternator

Jim,

I am not much into the detailed theoretical performance variations of HTTP or Non-HPPT. I figure this system will have a fairly long life expectancy and the cost difference for the HTTP controller over the expected service life is insignificant. Having done some research befor buying this stuff the HTTP seemed to be the latest available way to control things and I didn't want to NOT buy the best for the long haul.

I don't have to worry a whole lot about high temperature losses---I live in NW Washington near the Canadian border :-D

Jim

System2 · May 2007

Re: mppt charge controller versus my alternator

I am fairly concerned about high temperature losses. The location in which I plan to spend a good part of the late summer and fall is half way down the baja pennisula and just bakes that time of year. I am planning on rigging some sort of system in which I can manually aim my panel at the morning, midday, and evening sun, but I also would like the panel to be as inconspicous and aerodynamic as possible when travelling. Advertising wealth is just asking for unwanted attention. Displaying a 4.5 x 2 foot panel simply advertises that you have hungry valueable electronics inside and can afford la mortida. I was thinking of trying to mount my panel flush or even below he surface of my fiberglass roof as to keep it mostly hidden while underway but this will reduce the structural integrity of my roof and present drainage problems, and reduce the headroom inside. Also it will increase the temperature of the panel and my interoir. I spent the extra money on the mppt controller to squeeze out every watt I can. I'm not going to negate that by insulating the underside of my panel, but I don't think I can mount it with the regulation 4.5 inches above my roofline either. I've still got a while before I decide how I am going to mount it, disguise it and keep it effecient and aerodynamic. My RV is more a conversion van that I try my best to keep from looking like an RV. Maybee I can design some roof racks which incorporate my panel and keep it inconspicous till I decide to aim it at the sun.

mppt charge controller versus my alternator

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