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View Full Version : 12V DC to 13.8V DC powersupply



ZL1UZM
01-15-2010, 03:35 AM
I'm looking for a 12VDC to 13.8VDC powersupply. Can you recommend a good one? Obviously it has to be very RF quiet and put out 25Amps @ 13.8V.
TIA

VK2TIL
01-15-2010, 03:45 AM
What about an inverter and a 240v/ 13.8v supply.

Simple if not elegant!

Efficiency mightn't be too bad if you find a reasonable inverter and use a SMPS.

ZL1UZM
01-15-2010, 04:12 AM
What about an inverter and a 240v/ 13.8v supply.

Simple if not elegant!

Efficiency mightn't be too bad if you find a reasonable inverter and use a SMPS.

I need this powersupply for portable operation, so low weight, small size and high efficiencies are priorities.
At the moment I'm using a brandnew 28Ah sealed, liqiud acid m/c battery.
Even when fully (over-)charged, it cannot supply enough voltage to operate my rig at 100W. The voltage almost instantly drops down to 11.2V, which is half a Volt below manufacturer's specification. At 95% charge level the voltage drops to 10.5V. No good!!!

VK2TIL
01-15-2010, 05:05 AM
Usual solution to this problem is an extra cell or battery. If you could get 3 x 6v batteries you could regulate them.

There have been quite a few discussions here on the "12v/13.8v" topic.

Sounds as if your battery is "tired" or just not up to the job.

There are commercial products eg;

http://www.eham.net/reviews/detail/3404

I note that this one is discontinued but Google "battery booster".

They would effectively be inverters; "chop" the DC and transform & rectify for 13.8v.

Not too difficult to make if you are keen; the usual oscillator/FET chopper & transformer then diodes & capacitors.

Jaycar claim 90% efficiency for inverters such as this;

http://www.jaycar.com.au/productView.asp?ID=MI5104&keywords=inverter&form=KEYWORD

You would have to check for RFI, though.

KI6ZIF
01-15-2010, 05:06 AM
I need this powersupply for portable operation, so low weight, small size and high efficiencies are priorities.
At the moment I'm using a brandnew 28Ah sealed, liqiud acid m/c battery.
Even when fully (over-)charged, it cannot supply enough voltage to operate my rig at 100W. The voltage almost instantly drops down to 11.2V, which is half a Volt below manufacturer's specification. At 95% charge level the voltage drops to 10.5V. No good!!!

Now if i remember my math correctly. What makes you think a inverter will do the work for you?

Simply put you just do not have enough battery capacity, to run your rig at 100w. Adding an invertor into the mess, most likely will not fix this.

KC7YRA
01-15-2010, 05:07 AM
http://www.mfjenterprises.com/Product.php?productid=MFJ-4416B

There ya go. Never tried it but it sounds like what you need.

Brad

XU7ADQ
01-15-2010, 05:22 AM
Hi UZM; If you can find one, the Diamond GSV3000 is a real powerhouse.
http://www.elettronicagm.com/catalogo/alim/gsv3000.jpg
Fully variable 5-25v and delivers 35A! The 13.8v setting on the variable knob, is notched, and you can actually feel the soft click as you get to the 13.8v setting. The transformer is a monster though, so it's much bigger than a switch mode one (and doesn't create as much RF noise - if fact NONE). I believe they are now marketed under another brand name (compare the picture to other brands - it's identical). I saw this on the shelf in a radio shop in Phnom Penh, right at the back, and literally covered in dust (probably left over from the UN mission). I own the IC-706MKII-g, which is a renown power hungry beast, so was on the look out for something which would deliver at least 25A, so showed a little interest in the PSU, so the shop keeper wouldn't think I was very interested (the price in Cambodia doubles if they think you want something badly!:rolleyes:). He didn't even properly know anything about it, and in fact was powering his FT7900 on the bench, with a 10A Thai PSU! I asked whether it was for sale, and he said, ok $75! I showed no sign of being happy with the price, in fact I made as if I was shocked, and laughed and headed for the door (good buyer tactic in Cambodia - they need your money, and you want a good price). He called me back (as expected), and asked 'how much you pay'? I said 'if you show me that it works, I'll give you $40'. So he hooked up a Motorola VHF rig, and it powered up, so I asked him to transmit, and the meter on the right deflected, showing it was delivering the correct current without a buzz. Happy, I said OK, I'll take it, and there began the usual 10 minute barter process (remember the scene from Monty Python's Life of Brian?:D) To cut an already long story short - I walked out with a very well made and very expensive (new) 35A PSU for $50 US! Happy? Ohhhhhhhh Yeahhhhhhhh:D. Check around ebay or hamfest/rallies, for a used DIAMOND GSV3000, but if buying online, be prepared for high shipping, 'cos it weighs a ton! Good Luck!

XU7ADQ
01-15-2010, 10:19 AM
Looking at the OP, I thought it was a 12 TO 13.8v PSU that was needed.
Looking at the replies, am I to understand that you need something to up the voltage from 12v up to 13.8v, and if so, is that going to have any effect?
If the current is available, most rigs will work at the same rate from around 10v up to 16v (although above 15v should be avoided).
I think I've misunderstood the request, and if so, I'll go and stand in the corner with my 'D'hat on. :D

N0IU
01-15-2010, 10:38 AM
Even when fully (over-)charged, it cannot supply enough voltage to operate my rig at 100W.Reduce your power. If you can't make the contact at 50 watts, it is doubtful 100 watts will make that much of a difference.

G4ILO
01-15-2010, 10:41 AM
If the problem is not being able to run 100W on 12V, why worry, why not just run 50W? It will make little difference at the receiving end, but at half the current consumption you'll get a lot longer from the battery.

VK2AKG
01-15-2010, 01:12 PM
At 95% charge level the voltage drops to 10.5V.

If you are measuring battery voltage at the battery then it sounds like your battery is on its way out (or far too small).

If you are measuring battery voltage at the rig and voltage measured at the battery is OK then it sounds like your cables are undersized.

Of course you could be lucky and discover it is just corrosion at the battery terminals or a dodgy connector both of which would be cheaper and easier to fix.

Good luck,

73 Frank vk2akg

KJ4JGN
01-15-2010, 01:31 PM
I use a Pyramid PS-36KX, works well, low noise , over load protection, and was very low priced.

KI6ZIF
01-15-2010, 08:58 PM
I use a Pyramid PS-36KX, works well, low noise , over load protection, and was very low priced.
Don't ya hate it when you speed read and miss what the question was?



I need this powersupply for portable operation, so low weight, small size and high efficiencies are priorities.
At the moment I'm using a brandnew 28Ah sealed, liqiud acid m/c battery.
Even when fully (over-)charged, it cannot supply enough voltage to operate my rig at 100W. The voltage almost instantly drops down to 11.2V, which is half a Volt below manufacturer's specification. At 95% charge level the voltage drops to 10.5V. No good!!! Then again, when the OP refers to a voltage booster as a "power supply" this helps to further confuse people.



If the problem is not being able to run 100W on 12V, why worry, why not just run 50W? It will make little difference at the receiving end, but at half the current consumption you'll get a lot longer from the battery.
This is dead on accurate info.

OP: Your problem is, at 100w your radio needs X amount of amperage. The 28ah batteries you are attempting to use, are simply not allowing enough amperage draw @ 12v. This is common when the batteries are being over discharged (amperage) wise.

The only 3 "proper" solutions you can really use is.
1: Use larger batteries.
2: Lower your output power.
3: Verify your battery to radio interconnects are of the proper gauge to allow peak amperage draw, without significant voltage drop.

As already mentioned, 50w to 100w won't make a drastic difference on the receiving end of the transmission.

If your concerned about weight. Look into a 12v Absorbent Glass Mat or Gel Cell battery. These are generally MUCH lighter then "wet cell" (lead acid) batteries.

N4CD
01-17-2010, 01:48 AM
There are two currently available battery boosters out there for this purpose.....

MFJ makes one

THere is an N8 that sells more. One expensive but some folks think the price is worth it.

And in the past W4RRY used to sell a batter booster for about $75 that was popular with boat owners.

All used DC to DC switching boost regulators to take inputs down to 10.7 v and boost it up to 12.5 or 13.4V.....

Good for running voltage sensitive radios off batteries......

depending upon temps, most batteries will quickly drop to 12.4 or 12.2v under load when not being charged...and then go down from there.

W6EM
01-17-2010, 08:54 PM
Most upscale regulated low voltage supplies use remote voltage sensing for a reason. Drawing 25A even momentarily can easily drop the end point terminal voltage down a ways.

It could be a power cable voltage drop issue. After all, a loop resistance of only 0.1 ohms at 25A is, well, a drop of 2.5 volts to the radio.

So, in the interest of light weight, you've selected a 28Ah battery. That's 28Ah at an 8 hour rate, or an average of 3.5A demand over 8 hours. I suspect that the battery can't deliver the current and maintain terminal voltage. If you try a boost inverter, you'll only increase the current demand in order to boost the voltage.

Besides that, you'll have very little operating time on such a battery. Your receive demand is probably an ampere or so, at least. If you cut your transmitter current demand to say 3 to 4 amperes, at least you'd have a few hours of operating time. For your rig, you need something like a battery with maybe 200-300Ah of capacity.

I use a 7Ah gel cell on my IC-703+. I can operate about a day, comfortably, before recharging is needed, or, more to the point, a second battery to use while the first one's recharging. Receive demand is about 300mA with the lights off and about 1.5A when transmitting.

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