Other 12V Sources with a 24V-12V converter

[brulaz]

Switching to a 24V battery bank has gone well so far. The 40A Victron 24V-12V converter seems to handle all my 12V loads without issue. It keeps the V at about 13.2V

But a question: there can sometimes be other 12V sources, like the 120VAC-12V converter when on shorepower, or the truck's 12V alternator source when towing, or even the little 10W solar battery tender that came with the trailer. These are all wired into the 12V side and do not now see any batteries.

Would you expect any conflict with the Victron 24V-12V converter, or any issues because of no 12V batteries?

I know my mppt solar charger goes a little crazy when no batteries are present. It's scan to determine the mpp will send Vs all over the place. But it's now tied into the 24V battery bank and is happy.

Also know the 120VAC-12VDC converter doesn't require batteries, but will it interfere with the 24-12VDC converter. Should I turn off the 24-12VDC converter when on shore power?

Should I also let the truck's alternator handle the 12V loads by turning off the 24-12VDC when travelling, or just disconnect the alternator's feed to the trailer? I've already disconnected the little solar panel. The truck's alternator feed is harder to get to.

Thanks.

[brulaz]

BFL13 wrote:
Why keep the Victron 24-12 at 13.2 instead of say 12.6?

The Victron is non-adjustable as far as I can tell. But it is nice that no matter what I do on the 24V side (e.g. equalize at 32V) the Victron will keep the 12V side at a stable 13.2V.

[BFL13]

Why keep the Victron 24-12 at 13.2 instead of say 12.6?

[brulaz]

And, finally, I can say that all these 12V power sources seem to work well together.

When boondocking, the only 12V source is the Victron 24-12V converter with an actual V of 13.2V.

When on shorepower, with the WFCO turned on as well, the V goes to 13.6V and the current from the Victron (and batteries) drops to approx. few hundred milliamps (crude measurement with clamp-on ammeter).

And when plugged into the running truck, the V is ~14.1V via the alternator.

The Victron 24-12V converter stays on all the time. But by using these alternate 12V power sources, the load on the 24V batts is reduced which makes it a bit easier for the battery chargers to maintain them.

[brulaz]

Installed the Meanwell 27V (~26-32V) powersupply. Works ok, but, as Mex notes elsewhere, its potentiometer is very sensitive.
EDIT: and it actually did get up to 32.5V, when unloaded.

Also it does have a rather noisy fan that cycles in the heat and with small background loads. Unfortunately the only place I could install it was in the trailer's pass-thru, close to my head when sleeping (or trying to).

So now I only use the Meanwell as a shorepower battery charger when the batts need more charge than the solar can provide. And the old WFCO has returned as the primary 12V power source for appliances on shorepower.

Overall, the 24V conversion is working well. Got a peak 630W out of the 690W solar array the first day we boondocked and were using lots of juice. That's with a 30A MPPT controller. And the new 24V 2000W Kisae PSW inverter handles the microwave without any issues, so far.

Looking forward to getting out and working the system more ...

[brulaz]

MEXICOWANDERER wrote:
THIRTY Volts WILL TIDE YOU OVER JUST FINE. This ain't a Betty Crocker moment.

Yep. And thank you for the Meanwell suggestion.

CA Traveler wrote:
Using the most widely used temperature compensation formula:

-0.005 V per C per 2 V cell

Yields at 0C (32F) -0.005(0-25)12 = 1.5V for a 24V battery. And this implies that for ideal flooded bulk charging you would need a 29.6+1.5 or 31.1V charging source.
...

And that's what my solar charger does. Max is 32.5V
Temp compensated with probe at the batteries.

(But I've reduced the temp comp to -0.004V per cell per degree C)

If necessary on cloudy days and if I want to equalize or whatever, the 30V from the Meanwell will provide that extra ooomph for the solar to get up to the required V.

Not sure if some of you EVER see sunshine where you live ...

[BFL13]

Here is Mark's handy table again (scroll down) for 13.6 and 14.7

http://forums.trailerlife.com/index.cfm/fuseaction/thread/tid/26669731/srt/pa/pging/1/page/1.cfm

[CA_Traveler]

Using the most widely used temperature compensation formula:

-0.005 V per C per 2 V cell

Yields at 0C (32F) -0.005(0-25)12 = 1.5V for a 24V battery. And this implies that for ideal flooded bulk charging you would need a 29.6+1.5 or 31.1V charging source.

Not that I normally camp at freezing temperatures but it may be a consideration for some.

[MEXICOWANDERER]

THIRTY Volts WILL TIDE YOU OVER JUST FINE. This ain't a Betty Crocker moment.

[brulaz]

BFL13 wrote:
So when you go to the golf car place looking for their used battery deals you can pick 8v batts, not just their 12v batts.

The place I went to four years ago had 48v golf cars with 6-8s or 4-12s, and they seemed to be going over to the 8s for whatever reason.

I got two used 12v T-1275s, but you would be able to pick three-8s instead if you could fit them.

Forgot about the 8V batts!

But am putting a lot of attention and care into the existing four GC2s. Would like to get 5 yrs out of them at least. Even down to 25% SOC should get 750 cycles out of the US2200s (dunno about the Duracells).

Was concerned about charging two such dissimilar (age, brand, sp. gr.) 12V banks connected in series. So picked up up a Victron "Battery Balancer" that tries to keep two series 12V banks properly charged. It was not very expensive (and not very powerful). But so far seems to be working as advertised; the two bank's voltages when were mostly quite close (<0.1V diff), although I only monitored it that one time.

Wouldn't work with three 8Vs though.:(

And who knows what battery technology will be available and affordable if I can keep these ones running for 5 years?

[BFL13]

So when you go to the golf car place looking for their used battery deals you can pick 8v batts, not just their 12v batts.

The place I went to four years ago had 48v golf cars with 6-8s or 4-12s, and they seemed to be going over to the 8s for whatever reason.

I got two used 12v T-1275s, but you would be able to pick three-8s instead if you could fit them.

[brulaz]

BFL13 wrote:
I got lost there but don't forget 30v at 24 is 15v at 12 and in winter, 14.8 at 12 is 15.2 at 12.

So in winter you need 30.4 at 24 just to stay even, OR, you can chicken out and go Down South for the winter. 😞

Well, the main point of this trailer is so we CAN go South every winter. And that's what we do. But we do run into cold weather in the Southern Appalachians on our way to Florida. One early November we couldn't even get into Smoky Mountains N.P. because of heavy snowfall.

Anyway, the Meanwell RSP-500-27 only goes from 26V to 30V. The next one in the series goes from 41 to 56V, way too high at any temp. And the Meanwell is affordable, even in Canada, so that's what it'll be.

The mppt solar charger is temperature compensated so if the Meanwell's V isn't high enough the Solar should be able to boost it up, assuming there's any sun at all. At least that's how it seemed to work with our 12V battery system and the Prog. Dyn. charger.

[MEXICOWANDERER]

Meanwell RSP 27

[BFL13]

I got lost there but don't forget 30v at 24 is 15v at 12 and in winter, 14.8 at 12 is 15.2 at 12.

So in winter you need 30.4 at 24 just to stay even, OR, you can chicken out and go Down South for the winter. 😞

[brulaz]

BFL13 wrote:
One thing not mentioned IIRC is that some (many?) solar controllers have a positive ground. That doesn't matter when you don't ground your panels as with an RV installation. I have no idea, but might that be a problem when using a pos grd solar controller supplied with a typical DC-DC? ISTR your 24-12 is chassis grounded? Not a clue, just mentioning it.

Thanks for the caution. Just checked:

Rogue wrote:
The enclosure of the MPT-3048 is floating with respect to all circuit voltages and may be used with either negatively or positively grounded systems. It may also be used with systems in which neither negative nor positive are grounded, as allowed by NEC 690-41 for systems of less than 50 volts.

Will bear that in mind with any future PWM controllers.

And I just placed an order for the Meanwell RSP-500-27.
It's adjustable output V is 26-30VDC, with max 18.6A

Perhaps set it up to something around float V (~26.5V), and, as suggested, use the 24/12V converter all the time for the 12V systems (and forget the 120VAC/12VDC converter).

When needed I can boost its V to 30VDC to help the solar refill the batts after a rainy spell when I get to shore power.

(Will wait on the PWM and extra solar till next year, maybe.)

The Meanwell has an interesting remote control function across a couple of pins:
0-0.8V turns it ON
4-10VDC turns it OFF

And the Kisae inverter has a 5.1V USB port. Perhaps that port can be used to turn Meanwell OFF when boondocking and using the Kisae to provide 120VAC? One less thing to worry about if it works.