Higher-power DC 48V-12V converters?

RandomJoe · May 2009

A post on another forum has me thinking again about the feasibility of switching my system to 48V. They mentioned using a 48V-12V DC converter to power my ham bench.

I had thought about that in the past, but first hadn't found anything of sufficient power capacity with the right voltage input. I'd want something with at least 35-40A output, the only thing I found anywhere near that in my (probably brief) search at the time was from Samlex, and those were 24V in.

The other concern, of course, is it needs to be noise-free. It'd be completely pointless to use one if it's going to trash the RF spectrum while I'm trying to use my radios!

Anyone know if such a beast exists?

n3qik · May 2009

Re: Higher-power DC 48V-12V converters?

Might be the expansive way to do it, but could use a MPPT charge controller to a 12V battery.

BB. · May 2009

Re: Higher-power DC 48V-12V converters?

Many (most?) MPPT controllers do not have/meet FCC class A or class B ratings and probably are not very "quiet" anyway as they use PWM to finish up the charging of the battery bank.

Also, if you are charging a battery to run your HAM--you are going to have the losses of both the controller and the battery itself (although, an AGM 12volt battery will be pretty efficient if you are mostly floating it instead of cycling it).

Can you use 120 VAC with an inverter instead? Efficiency wise, it would probably be about the same efficiency as a voltage converter. Wires would be smaller and you have the isolation of the radio's AC input stage.

If you need really quiet DC power--using two 12 volt banks, one under load, the 2nd charging could work (I had a co-worker decades ago that suggested this setup for use on a Mars space craft where the absolute voltage was not as important as having a quiet supply was).

-Bill

RandomJoe · May 2009

Re: Higher-power DC 48V-12V converters?

Doh! I forgot about that - and had even considered it at one time! I'll have to see if I can find the notes I took back when. Think I was considering the Morningstar MPPT, can't remember if it works in that application - seems like one or two I looked at said they could not be used in this application... I already have a 100AH 12V AGM that was my first solar system battery - been wondering what to do with it, this would be a fine idea.

On a related note, how much time is "too much" between new/old batteries? I currently have six T-105s, and if I want to use this bank at 48V anytime in the future, I'm figuring I ought to get a couple more soon. I bought the first six back in Feb/March.

BB. · May 2009

Re: Higher-power DC 48V-12V converters?

Roughly, we guess that the new batteries (especially those used in parallel or series/parallel) operation will average out to last about as long as the older batteries... So, in your case, with the batteries only a few months old--should not be a big issue.

The batteries, as they cycle the first 10+ times when new, tend to work better (more capacity, lower internal resistance)--so the Newer batteries may not have quite the same performance as your older bank until they cycle for a while.

The only solar controller out there, than I am aware of, that has FCC Class B for the current range you need (45+ amps @ 12 volts) would be the Xantrex XM-SCC 60. Probably one of the best units out there right now.

Perhaps Solar Guppy can address the question of using a 48 VDC battery bank as its input power source--Otherwise, you may need to Call Xantrex directly (and, they may automatically say no as this is an un-spec'ed, untested use of their controller).

-Bill

RandomJoe · May 2009

Re: Higher-power DC 48V-12V converters?

BB, the AC inverter would be what I could do immediately - it just seemed "silly" to have a DC battery bank, convert to 120VAC, just to run a power supply producing DC again! Thus why I went with the 12V bank in the first place. Less points of failure too, which is certainly a design idea I consider worthy!

Of course, my "workhorse" power supplies are old Astrons with a huge hunk of iron (transformer) in them so not necessarily the most efficient things in the world. I do have a couple of switchers now although they are smaller. Well, I guess I do have one *large* switcher - the Iota 55A unit I use to recharge the 12V bank if needed. I could use that as a PSU if I went 48V.

I'm not a real "purist" when it comes to quiet, I just don't want noise spikes all up and down the band when playing with the radios. So far, my Outback FM-80 has been just fine, I haven't noticed any noise with it. Others have, of course - it could easily be I just have enough other noise around that I don't notice it! Being in the middle of a city can be a problem...

The main reasons I have given any real thought to 48V were to make it easier should I want to relocate the ham bench in another room (I'm single, so the whole house is my playground!) since I wouldn't have to run such fat wire. And in the future I think I'd like to go ahead and move more of the house off-grid or just grid-tie the whole thing so excess power gets pushed to the rest of the house. (I doubt I'll ever actually get to the point of spinning the meter backward.) I think I could still do that with 12V with the Outback gear, I had originally looked at Xantrex XW and IIRC that requires 48V - or at least won't do 12V.

BB. · May 2009

Re: Higher-power DC 48V-12V converters?

The Xantrex XW is an entire product line--not just the solar charge controller (XW being the common "model name" makes it confusing).

The XW Inverter is 48 VDC only for their larger products (they do have a smaller 24 volt 4kW inverter too)--However, the XW-SCC charge controller is programable for its proper output.

If the Outback works well for your application--then it is hard to argue with sucess.

I agree that going to 120 VAC to then back to a 120 VAC to 12 VDC charger is probably a waste of money (and probably not as efficient).

Getting a Kill-A-Watt meter and measuring your power usage with an AC to DC charger would quickly show how much extra power it may cost you.

-Bill

niel · May 2009

Re: Higher-power DC 48V-12V converters?

joe,
i do fine without a power supply and only used a battery with a pv system to charge it for operating my radios. i never looked for noise from my sb50, but there wasn't any that was that objectionable for me to isolate it to see if the controller had contributed. i have an rs35 supply that kept popping the lm723. that astron ps is still sitting here unused and unfixed as my solar supply outdoes the astron hands down. i just have to watch i don't yack so much as to drain the battery below 50% as my battery is also around 100ah. in hind side i should've gone for at least about 200ah.
i'm not sure if i'm reading exactly what it is you're looking to do. do you want 48v pvs to charge your 12v battery or 48v pvs to charge a 48v battery bank? if you want a 48v pv system charging a 48v battery bank for the house, i'd keep a seperate number of pvs and appropriate batteries for the 12v ham operations. i look at this like not having the lights in a room on the same circuit as the outlets for if it goes, it all goes when on one system. large capacity converters, if you find one, will most likely be expensive enough that a battery would be afforded. (i could be wrong on that last point) if you do run short on ah capacity for your seperate solar ham setup then you can rig up a small cheapo charger through an inverter to supplement it until it can be recharged with solar.

mike95490 · May 2009

Re: Higher-power DC 48V-12V converters?

If you can use 12V @ 10A, nice clean DC from a 48 V -> 12V converter, there is a $70module for this. See my post :
http://forum.solar-electric.com/showpost.php?p=19587&postcount=8
http://search.digikey.com/scripts/DkSearch/dksus.dll?PName?Name=454-1190-ND
mfg: http://www.powerconversion.com/products/websheet/365/AEO

RandomJoe · May 2009

Re: Higher-power DC 48V-12V converters?

Niel, this is pretty much a classic case of "the system grows over time"!

My original intent with this system was primarily as backup in a power outage, keep some lights and a laptop along with the radios going so I wasn't just sitting here in the dark with nothing to do. I'm now to the point I can also accommodate keeping the fridge going overnight / when I'm gone and don't want to leave a generator running.

Thus, my initial decision to go 12V. All the radios are already there, and I have a collection of low-wattage lighting that is also 12V - a couple fluorescent fixtures, and for truly low power some LED lights that - while too garish and cold for normal use - provide a nice amount of light for almost no power. (I went crazy with the PowerPole connectors at one point - I can plug anything into anything else now!

)

However, I have a couple of potential plans / desires on the horizon that might be better served using a higher voltage.

First and foremost, the good 'ol "use every watt" desire. My system will frequently hit float by 1PM. It'd be nice if I could make use of the rest of that power. But I don't have anything that I could use as a diversion load, it would be "easiest" (inspections and red tape aside) to grid-tie the whole thing and let that extra power feed into the house to help with supplying the fridge, or whatever might be on.

I'm not too keen on messing with the grid-tie requirements, as I seriously doubt I'll ever put enough PV on this house to truly backfeed the grid. So the next-best thought was to install a sub-panel with a couple circuits to "critical" loads like the fridge, then power them 24x7 through an inverter that was set not to "sell". It's been six months since I looked at this, and I can't remember for sure, but seems like the Xantrex XW at least could be configured to power the subpanel loads off the main, then supplement it with excess PV power. But perhaps it could only switch between the two, thus my thought that grid-tie was the only real option...

At any rate, my original plans back when were to use Xantrex - and their inverter required 48V. Again, I think the Outback system will work with 12V - I know they have non-grid 12V units.

Another idea would be to be able to run the furnace off the battery bank as well - in a pinch. That's pushing it for a 12V system though! Also, I have two rooms in the house where I like setting up the ham bench. One (where I am currently) is right on the other side of the wall from the battery bank, so no problem feeding it. The other is clear at the other end of the house, and by the time I accounted for the largest (though seldom-used) load the wire size required to supply 12V with minimal drop to the back room was ridiculous.

What might be interesting is to hook everything up to one of my power supplies through an inverter and compare how much power I draw that way over X time against feeding directly. I guess that would tell me how much it would cost to just use 120VAC for that feed. I already have a dedicated "generator circuit" that isn't tied to the grid system, which drops an outlet in the back room, kitchen and garage right beside the RE system. I could use that to power things off the inverter when I'm not using the generator.

The reason I don't have a second system just for the radios is that the ham bench is really my *only* primary load! I'm pretty much backwards to just about anyone else in this - feeding power to other items in the house is more of a "diversion load" for me, just a way to make maximal use of my system. (And an excuse to get new toys and hook them up!

) It isn't cost-effective, but it's fun.

I'm primarily just looking at requirements for future possibilities. One of the more pressing concerns is the fact that I only have six batteries, so might want to get two more fairly soon to have an equal-age set should I opt to go 48V.

niel · May 2009

Re: Higher-power DC 48V-12V converters?

that's a tough one to answer now i can say that although in your mind ham is primary, but from a load standpoint it isn't as those supposed secondary loads will far outweigh (at least in possibility) those of your simple 12v needs and is what is pushing this whole thing over the top. what are you going to do if you decide a 48v system to run everything with appropriate converters for the 12v stuff and find out that between your fridge and furnace that you won't be able to talk long if at all due to your other loads sucking down all of your backup power one winter's day because of an ice storm knocking things out? i think you can still go with the 48v system, but thinking of what i may do under the same circumstances, i would keep it separate from the primary 12v loads. this would be basically a home backups on 48v that you could expand on with more pvs as the basic charging is covered from the built-in battery charger. adding pvs to it is easy from there and this could be sell or nonsell, your choice.
if i understand it all, like i said, this is just what i'd do as i had thought about it from your perspective before and i'd want nothing to interfere with the communications and so i'd use separate systems. this also eliminates all of those converters. if you find your comm setup going short, but there's still juice for from the other available, then you can utilize another charger going from the 48v battery bank to your 12v bank. this may not be the most efficient way, but it is very practical and workable in my view.

RandomJoe · May 2009

Re: Higher-power DC 48V-12V converters?

You do have a point. That's the primary reason I was interested in grid-tie, as if the grid went down then the inverter would stop supplying power to the rest of the house - I just don't want to mess with all the red tape! (I'm not too keen on going "under the radar" with it.) And I never really thought too much farther down that line for the subpanel - I was pretty much planning on just having "critical" loads on there that I would want to be powered anyway (like the fridge). But that wouldn't use everything the panels could produce either.

Grr. Looks like the only relatively straightforward path to do what I want is grid-tie, but what a pain... Especially when it appears the electric company would charge me a "small fee" for the plan that would swamp whatever "savings" I might see - especially when I would probably never push any watts into the grid! (And there's a bit of a rub there too - I bet I *do* push just a smidge at times, since midafternoon I'm still at work and little is going on in the house. I'd more than make up for that as soon as I get home and turn stuff on, but...)

Ah well. We'll see!

My primary problem with two systems is roof space for panels. The only piece of south-facing roof I have is relatively small, and will hold eight of the 135W panels I'm buying now in two rows of four. I do have *LOTS* of west-facing roof (although the chimney makes some of it less desirable) but of course take a hit on efficiency there. The east side is heavily shaded by a large tree.

I need to decide just how far I want to go with all this here. More and more often lately, I keep having these daydreams about purchasing a large chunk of land (as in "can't-see-any-neighbors" large!) somewhere out of town and going crazy with some projects I just can't do here in town on a small lot!

I'd hate to get deep into it here, then have to move it all and patch things up before selling.

...and now I think I'm just rambling!... :roll: Thanks for all the thoughts! :cool:

n3qik · May 2009

Re: Higher-power DC 48V-12V converters?

Let me reinforce the KISS rule.

I have 900 watts of panels with a 12 V system. I am using a PWM C60 charge controller. On good days last week, I can do 4400 watts and also have charged batteries.

I am staying with 12V due to all my night lights, cable modem, router, smoke detectors and EeePC are wired to the batteries.

You are in the same boat I am in. Most of you loads are 12V.

RandomJoe · May 2009

Re: Higher-power DC 48V-12V converters?

You are, of course, correct!

But I'm a tinkerer who can't keep his hands off anything!

n3qik wrote: »

...and EeePC are wired to the batteries.

Ooh, I've been thinking about that. I noticed my Eee uses 12V, but was worried about just powering it directly off the batteries, since they go up to 14.2V during charge. Is this what you're doing? And if so, it works just fine? That'd be nice... I currently have a "car PC" Atom-based system that pulls 25W without a monitor. Being able to drop that to 10W with an Eee would be very nice indeed...

n3qik · May 2009

Re: Higher-power DC 48V-12V converters?

The 900 16G from Best Buy will take up to 14.0 VDC. I did have it go to 14.7 V but started to smell the magic smoke. I plan to get a switching regulator to regulate the voltage.

Also have a 1002HA, but that is using it's PS on the inverter.

I like to tinker also, That is what stopping me from getting the XW 4024, No fun there, just wire it in, set it once, then sit back.

AntronX · May 2009

Re: Higher-power DC 48V-12V converters?

This one will do 30A for short time, 20A continuous. http://www.powerstream.com/dc48.htm If it's noisy, you should be able to add some chokes and capacitors to make it cleaner.

System2 · May 2009

Re: Higher-power DC 48V-12V converters?

I'm a newbe here but this might help. I work for an industrial material handling equipment supplier in Texas and we use this converter on some of our battery powered equipment. It is a 48/36VDC to 12VDC converter rated at 300 watts. Here is the link, I think it's rated at 25 amps and is UL approved.

http://www.sevcon.com/PDFs/DCDC%20Converter%20DC1104EN.pdf

niel · May 2009

Re: Higher-power DC 48V-12V converters?

too bad they don't have a variable output or can make it able to have say a 2 or 3 stage charger as the output as i believe this is what many would want or are looking for in a converter as many do not have another charging source going to said battery on the output.

Higher-power DC 48V-12V converters?

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