24 volt to 12 volt converter

The lower voltage charger does not add its full amps right up till when it is passed by the higher voltage charger. The lower voltage charger starts to taper in amps before the battery reaches the voltage of the other one. So they do add their amps right to the end but the total amps tapers until only the full amps of the higher voltage charger are still going in. Then those amps taper after a while too as is normal.

Actually you get all sorts of tapering. You can have both tapering but the lower one starts first. It depends on the proportions of their "spreads" between charger and battery voltage, battery AH, total amps, and SOC.

BFL13 wrote:

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You don't have to match the voltages exactly to get them to add their amps, but the closer they are the longer they will keep adding their amps before the higher voltage one takes over and the other one is left in idle.
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That seems to generally happen with multiple power sources in constant voltage mode.

Our Victron 24-12VDC converter (actually 13.2V) was happily pumping out amps until I plugged in the WFCO 120VAC-12Vdc converter (actually 13.6V). The Victron just stopped.

Similar thing happens when I plug in the truck's 12V line. When the engine/alternator is running (~13.6V back at the trailer), the Victron drops out. But when the engine is off, the Victron 24-12VDC converter is maintaining the truck's 12V batteries at 13.2V.

A more elaborate example is with our Rogue Solar charger and the Meanwell power supply. The Rogue switches to constant V absorb mode at 29.6V and the Meanwell's constant V was set to something a little less than that.

In this one case, the batteries were depleted and the Meanwell was plugged into the truck's 120VAC inverter that I could monitor as we drove home. The trailer's solar was running and initially in bulk/mppt mode. Initially the truck inverter's wattage was the Meanwell's max of ~630W, which slowly declined to about 250W after a few hours. The wattage then went from 250 to 0 and back and forth for a while, then finally just stayed at 0. I then went back and checked the trailer's solar controller and found it in Absorb mode.

So I guess once the solar passed the Meanwell's V setpoint, the Meanwell dropped out, but then the battery V dropped enough for the Meanwell to come back on again, and repeat, until the batteries+solar could maintain a V above the Meanwell's setpoint.

Interesting stuff, and it all sort of makes sense, amazingly.

The 20 amper will be fine for that job as described. Excellent price for that and the extras too.

You don't have to match the voltages exactly to get them to add their amps, but the closer they are the longer they will keep adding their amps before the higher voltage one takes over and the other one is left in idle.

The Tracer has a fixed charging profile of getting to 14.x, then staying there for two hours, then dropping to float at 13.x (the x depends on the battery type selection you set it for) The remote or the computer way lets you change that profile somewhat, I haven't really looked into that. I like its fixed profile for our situation.

So besides the voltage matching to keep them adding in Bulk the longest, you might have some difference during or after that two hours of Absorption if one stays at Vabs longer.

However--since the portable is for when the roof set is out of the sun, you don't care if they match.

BFL - The 20A model (the A version) with remote display and temp probe is already on a boat from China. Who knows when and if it will arrive, but for C$130, decided to risk it.

And as I have a 24V battery bank, its 520W @ 24V rated power should be ok. Can't imagine carting out and setting up more portable panels than that.

My understanding was that you needed the separate display to modify the battery charging parameters? I wanted to match the settings in my Rogue mppt for the permanent panels. Anyway, the remote display will be nice to have right next to the Rogue's.

Almot - my other MPPT controller (Rogue 30A) for the permanent panels was a lot more expensive and has everything you say. The Tracer has remote temp compensation and very adjustable parameters from what I've read, but lacks the remote V sensing (not necessary in my case), Absorb termination based on current, and logging (though you could connect a pc/tablet and perhaps log there). But as it will be a secondary/supplemental controller, I think/hope it will be fine.

And yes, BFL, and many others here have been very helpful on this journey.

brulaz wrote:

That's where we're going. A couple of 12V 6x6 170W panels to supplement the 690W on the roof (and often in the shade around here). 1mx1m and 26# each, so portable, but about as big as I want to go for portable. Will run them in series and have one of those cheap Tracer MPPTs on order from China (BFL13 seems to like his).

BFL likes all of them. From $12 Ebay toys, to slightly better PWM to half-ars single-panel EcoW MPPT, eventually graduating to more-less substantial Tracer - still kinda 3-speed auto transmission of a 1950 Japanese cars, but close to real thing already.

Not that there is anything wrong with enjoying all things around you :)... I wish I could enjoy toying with it, unfortunately my priorities were to make electronics work, messing with it as little as possible (part of the reason was that my messing with these things wouldn't have resulted in anything good). Bought fully-featured 30A MPPT with warts and all - V sensing, remote T-comp, display, log, current-based and timer-based Absorb, online connectivity (that I don't need) etc etc. And called it a day. Cost me just about what Tracer 40 sells for on Amazon, if you add all the accessories. Wasn't as much enjoyment, but didn't contribute to heaps of electronic refuse either. I have to say though, that BFL ugly solar graphs (among other info on this forum) helped me a lot to get where I wanted to. Despite all the warnings from the authors that solar project can not be estimated, planned and executed like you normally do with everything else.

Do get the bigger amp Tracer though. My 20 is too small. The 30 or 40 is only a couple bucks more and can do way more. Also be sure to get the 4210A not the RN version since their specs show the A can do more watts than the RN. You do not need the remote display that costs about $50. The unit has a display. Your Trimetric also tells you some of what the solar is doing--probably all you want to know most times.

Almot wrote:

tdevery wrote:
I like the idea of having at least 200watts for power if needed. I pick my campsites on google earth to try to get some sun. But with older state parks in PA, this is hard to find.

You will like it better having 200W portable and 500W permanent :)
Permanent will work on the road, and on open camps, and (a little) under the trees. It still works in leafy shade on a sunny day - poorly - but it works all the time.

You already have 40A controller for 500W permanent. Being MPPT, it can accept 24V panels, they are cheap per watt. Your 2 portable arrays will need 15-20A PWM controller, one for both, it can be found for ~$50. It is not likely that you will have to use both PWM portable and MPPT permanent at the same time, but don't see anything that would make such a pairing impossible.

That's where we're going. A couple of 12V 6x6 170W panels to supplement the 690W on the roof (and often in the shade around here). 1mx1m and 26# each, so portable, but about as big as I want to go for portable. Will run them in series and have one of those cheap Tracer MPPTs on order from China (BFL13 seems to like his).

MEXICOWANDERER wrote:
I love this new math where 1+1 = 2.5 and watts have nothing to do with "I" or "E" energy vanishes without a trace. Kirchoff, is rated higher than Polish vodka. Oh well...time to listen to a little Tom Petty.

"..and I won't back down.." Another good one gone to that Studio in the Sky.

Almot wrote:

tdevery wrote:
I like the idea of having at least 200watts for power if needed. I pick my campsites on google earth to try to get some sun. But with older state parks in PA, this is hard to find.

You will like it better having 200W portable and 500W permanent :)
Permanent will work on the road, and on open camps, and (a little) under the trees. It still works in leafy shade on a sunny day - poorly - but it works all the time.

You already have 40A controller for 500W permanent. Being MPPT, it can accept 24V panels, they are cheap per watt. Your 2 portable arrays will need 15-20A PWM controller, one for both, it can be found for ~$50. It is not likely that you will have to use both PWM portable and MPPT permanent at the same time, but don't see anything that would make such a pairing impossible.

Yes, I did (of course it was me :) ) I ran two controllers on the one battery bank. One PWM and one MPPT. All you need (but it can be off a bit) is to have them at the same high voltage set-point, so they will add their amps all the way up to Vabs.

You can still gets lots of time when they will add their amps if one is a bit lower in set Vabs. If you have long sunny day it just doesn't matter-- it all gets done no matter how theortically imperfect your set-up is.

Mr Wiz gets it. It is all about the inverter alarm. Some 12v inverters have an 11v alarm and 10.5v shut off. Others have no alarm until 10.5 shut off ISTR. They also specify a range above or below that where it will go off so it is luck of the draw what yours is.

It appears one 24v inverter has that 22.3 alarm, so you get a little more wiggle room than with 11 at 12 before it goes off. But you might get that wiggle room with a different 12v too.

Meanwhile the real voltage for the alarm depends on your wiring between battery and inverter because the inverter goes off depending on what voltage it "sees", not what the battery voltage actually is.

So that can skew any comparison between 12v and 24v for when the alarm goes off.

From all this, I don't see where it is "worth it" to go 24 vs 12 if you are getting it done at 12. If you can run the microwave while the batteries are at 50% that's all there is. You will be recharging those batts now anyway.

If you can't run your microwave at 50% SOC, then going 24v isn't the cure. Just add batteries or use fatter wire from inverter to battery. That has to be easier than going 24v and buying new inverters, etc.

Exception might be a small RV where you can't add space or weight. In that case, go AGM vs Wet. The 12v AGMs have much lower voltage sag so the inverter will not alarm so soon as with 6v Wets. You can carry two 12v AGMs and do as well with high voltage draws as with four Wets. Of course you only have half or less AH in the bank, so you need to do a 50-90 recharge every day instead of every second day.