Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: Battery Booster to raise voltage  (Read 8373 times)
KB0RDL
Member

Posts: 22




Ignore
« on: September 13, 2011, 06:22:31 PM »

I have assembled a portable power station consisting of two (2) Size 31 lead/acid deep cycle batteries of the type used for trolling motors.  These are new and wired in parallel to store and provide 12.6 volts in fully charged condition.  The rating of each battery is 140 amp hours but to get this close to this much they would have to be discharged at no more than 5 amps per hour apiece, about what it would take to run a QRM station on 5 watts plus provide a small amount of light from a few LEDs.

For about 6 to 8 hours a day I use a bi-pap breathing matching to sleep with.  It ordinarily runs on 110 volt house current.   The machine keeps me from going into sleep apnea and is necessary for my health.  In emergency the electricity to run the bipap machine (essentially a blower with precise pressure settings that change with inhaling and exhaling) would come from my two deep-cycle batteries through a 110 volt converter that is rated at 400 watts maximum.

What concerns me about this is that some devices will not run when the DC voltage drops below a certain point, which would be the case as the batteries discharge beyond a certain point.  Even when fully charged a strong load will drop the voltage slightly, but when the batteries are 50% discharged this tendency becomes very pronounced.  I had a mobile dual band radio that would not run when the current dropped below 12 volts.  Other radios would operate down to below 11 volts at low power.  I’m not sure how my 110 volt converter would respond to low voltage but I suspect there would be problems.

MFJ has a unit that claims to boost the voltage of a battery that has discharged below 12.6 volts back to that amount.  This is the MFJ-4416B Super Battery Booster.  Attach one side of the unit to the battery and the current coming out the other side is back at 12.6 volts.  The catalog info says that it has several adjustments and claims that it can “boost input voltages as low as 9 volts up to the desired 13.8 volts at up to 25 amps peak with a typical efficiency of close to 90%.”   

This sounds pretty good and I’m wondering what the downside is, besides the cost of $149.95.  Does anyone have any insight to offer?

Laird, kbordl
Logged
W8JX
Member

Posts: 5455




Ignore
« Reply #1 on: September 13, 2011, 08:31:43 PM »

I question the wisdom of using a battery booster because it increases power loss and makes it possible to drain battery too far. I would suggest you take some of that money and buy a 3rd deep cycle battery and run 3 in parallel. This will give you more stable voltage under load and even greater run time. On inverters, generally they work down to about 11 volts or so before they cut out. Also while you may of had a radio that cut out at 12v, my experience is that they will go much lower but output power can suffer.
« Last Edit: September 14, 2011, 05:20:31 AM by W8JX » Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
K7RBW
Member

Posts: 386




Ignore
« Reply #2 on: September 14, 2011, 05:36:36 AM »

I haven't heard of any problems associated with the "battery boosters." All they are are a DC/DC converter that will "boost" and stabilize the output voltage as the battery voltage drops during discharge.

The good news is that you get stable DC output throughout the battery's natural discharge cycle. The bad news is you'll use a bit more current from the battery in the process (to "pay" for the cost of voltage conversion). It just depends on whether having a stable output voltage is worth the reduced run time of the battery.

IIRC, the booster has a selectable cutoff voltage to prevent deep discharge of the battery. But you can see the problem...With a stable output voltage, you won't have any sense the battery is running low by looking at the attached gear. It'll work fine until, "poof!" the unit switches off. So, if having some warning is important, you'll probably want to monitor the battery voltage directly so you can see how close to your cutoff voltage it's getting.

As far as your bi-pap machine goes, you might see if it runs on 12-volts directly, if you haven't already. If it did, you could skip the inverter and save some efficiency.
Logged
K5LXP
Member

Posts: 4448


WWW

Ignore
« Reply #3 on: September 14, 2011, 06:05:59 AM »

Right out of the manual:

Selectable Minimum Input Voltage:

You have the choice of the minimum input voltage the MFJ-4416B will operate on. Set from the factory at 10 volts you can select 9 or 11 volts. This keeps you from possibly over discharging your battery and damaging it.

It is even latchable so once the voltage drops the Boost Regulator stop until you remove the power from the unit.

Audio Alert Feature: When enable instantly alerts you when the input voltage drops below the preset level.


Mark K5LXP
Albuquerque, NM
Logged
KB0RDL
Member

Posts: 22




Ignore
« Reply #4 on: September 18, 2011, 12:27:28 AM »

Well, you're probably right about just buying another battery.  The MFJ thing sounds good but the expense is considerable for something that's going to run a battery down faster.  I was concerned about voltage drop.  I live in the Kansas City area where we have occasional ice storms and power outages that can last for a day or so and sometimes several days and what I wanted was something for emergency power that might need to last for several days.  Thanks to all of you for your comments.  I appreciate it.
Logged
AB3NK
Member

Posts: 27




Ignore
« Reply #5 on: September 18, 2011, 10:22:01 AM »

The bottom line is that you do not get something for nothing.
Unfortunately - your plans were not well thought out, because if you would have asked before starting this project, we could have advised you of a better solution.

First off - the batteries you have are a poor example of a back up power supply. 150 amps is not a lot of storage, at that rate you would need5 of those batteries to compete with the one battery u have under the hood of most new 8 cylinder pick up trucks on the road today.

What all this means is that you have approximately 1/3 as much power available as you would if you had just one automobile battery.

Because we do not know where you live or your situation, there is no way for us to look at the service records of your utility supplier, most in suburban applications has less then 5 minutes per a year of drop outs.

In my area of the country, the average is about 6 hours per a year, with a major storm knocking out power anywhere between 1 hour and 3 days depending on the severity.

The other side of the coin is that the utility infrastructure is much better today then it was 20 years ago - hence even if the power does go out, they can back feed power into the grid at times to get most areas back on the grid faster then you can get out a emergency generator and hook it up and get it running.

You aren't going to DIE if your breathing apparatus stops working for a couple of hours, you will just not have one good night of sleep that night.

On the other hand, most equipment is not 12 VDC but 120 VAC and running a converter 12 / 120 is usually about 50% efficient at best.
The loss in the convertor consumes more power then the equipment you wish to run uses other then lights or a television which wastes a great deal of power in heat.   LCD's are probably a lot more efficient then others.

If you look at some back issues of QST you will see articles about people who built whole house systems that works on and off the grid.  Solar power panels which recharges the batteries - battery banks of thousands of amps of power, transverters that makes enough power to even run the air-conditioning and furnace.

I would expect one automobile battery to make enough power to supply enough power to run your medical equipment for one 8 hour period of time, but not a couple of boat batteries.

Using the MFJ would most definitely kill the batteries.
You don't seem to understand what the purpose of the MFJ is.

Ham radios requires about 13.5 VDC of power to operate efficiently.
Even as low as 12 VDC they will still work.
Below 12 volts - the radios will either cut back on transmit power and squeeze the electronics until finally failure occurs or they will stop working all together when the voltage gets too low.

The purpose of the Super Battery Booster is to throw away battery life in exchange for a little more radio time.
If you know that you need 13.5 VDC and the battery only has 12.8 when fully charged and will drop down to about 12.3 after about a hour and you want to protect your valuable radio equipment, they you use the super boost - which takes the voltage back up to 13.5 even when the battery only has 11 volts - until finally somewhere down the road, the battery discharges to the point of no return and you have to charge it anyways because the radio quits working.

The down side is - the Super Battery Boost is only about 75% efficient, which means it wastes about 25% of the battery reserve, which could have been used to run the radios in the first place.

It's easier to charge a battery when it only has 11.5 VDC / then when it has 10 VDC and will not hold a charge for very long because it has lost it's reserve because it has been discharged too far and the battery has failed.  There is no battery that is indestructible.

The purpose of the MFJ super battery boost is to supply power to run your radio one time in the event of an actual emergency when it is essential that you have power, such as a tornado, hurricane, nuclear disaster, fire, flood, etc.
When human lives are on line - what do you care about one or two automobile batteries?

It kind of makes me think of that Vietnam movie - "We Were Soldiers" where they asked the Colonel if he would like a rifle and he said when the time came that he needed one, there would be plenty of them laying on the ground.
Logged
AA4PB
Member

Posts: 12673




Ignore
« Reply #6 on: September 18, 2011, 01:17:41 PM »

Actually you can buy good quality DC to 120VAC inverters that will operate down to 10VDC, at which time they will shut completely off to protect the battery. No lead-acid battery should ever be discharged below 10VDC or its operating lifetime will be reduced. You should NOT use an automotive battery because they are designed short term use in starting the vehicle. You can't take them down to 10V very often without causing damage. You need what you have, deep discharge batteries. SLA or glassmat may be better in your application because they are completely sealed and better suited for indoor use.

You can also buy DC to AC inverters that include a managed charging and change-over circuit. They power your AC device from building power when its available (while charging the battery) and switch to battery power if the building power fails.
Logged
AB3NK
Member

Posts: 27




Ignore
« Reply #7 on: September 18, 2011, 04:29:34 PM »

I will agree with AA4PB - to a point.
The point usually is that we don't normally use automotive type wet call batteries indoors due to gas build up and venting.
However - if installed properly in a well ventilated area - and properly maintained - they will work just fine.

One thing that does impress me is the design of these new AC / DC battery chargers / maintainers that takes some of the drudgery out of  battery bank maintenance.

One brand that comes to mind is the Battery Tender which monitors the condition of the battery and also keeps it from calcification and other issues.
http://batterytender.com/
Logged
N8EMR
Member

Posts: 234




Ignore
« Reply #8 on: September 19, 2011, 02:35:38 AM »

Why bother with the DC/AC conversion at all. Doesnt the bpap power from a wall wart? If not you might look for a
version that does. my bpap is DC powered through a wall wart. Its not 12v, but dc/dc is a little more efficient than dc/ac

Logged
W8JX
Member

Posts: 5455




Ignore
« Reply #9 on: September 19, 2011, 05:21:57 AM »

I will agree with AA4PB - to a point.
The point usually is that we don't normally use automotive type wet call batteries indoors due to gas build up and venting.

This is greatly over played. The only time a battery will tend to gas some is at very high sustained discharge and charge rates. Long ago batteries used to gas more and it was common to have to add water to cell (water boils off but not acid) but today it is not a issue due to design changes and most batteries are sealed anyway do not vent any gas unless pressure is very high. Trapping gas helps it recombine when battery is resting and maintain proper electrolyte level over life of battery.
Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
AA4PB
Member

Posts: 12673




Ignore
« Reply #10 on: September 19, 2011, 06:17:26 AM »

I guess you could also say that storing propane gas containers inside your home is greatly overplayed too. After all, as long as they don't leak and nothing goes wrong they are perfectly safe.

I would never use an automtotive type wet type battery inside my shack or house. You never know when you could have a short, charger defect, or bad cell that might cause excessive gassing or a spark on one of the connections to cause ignition. Its the same reason that they tell you to make the ground connection last (away from the battery) when jump starting a car.
Logged
KF4BAE
Member

Posts: 7




Ignore
« Reply #11 on: September 19, 2011, 09:18:18 AM »



First off - the batteries you have are a poor example of a back up power supply. 150 amps is not a lot of storage, at that rate you would need5 of those batteries to compete with the one battery u have under the hood of most new 8 cylinder pick up trucks on the road today.



I think you're confused about CCA and the amp hours available in a battery deep cycle battery.  The rest of your post seemed pretty good.
Logged
LA9XSA
Member

Posts: 376




Ignore
« Reply #12 on: September 19, 2011, 02:55:52 PM »

The main issue here isn't wet vs. sealed. It's starting batteries vs. deep cycle batteries. Starting batteries have their lead as a sort of foam, which helps deliver high current when running a starting motor, but will easily sulfate and be destroyed if discharged too much. Deep cycle batteries have solid lead plates, which won't deliver as much current, but will survive deeper discharges.

For portable use, I would use a gel or AGM battery, but for a stationary in-home system an old style open wet cell battery might be more economical, if you have a good ventilated place for them, a good charger and top up the water occasionally. Whatever inter-plate medium you go for, get a solid plate deep cycle variant that also keeps charge reasonably well.
Logged
KB0RDL
Member

Posts: 22




Ignore
« Reply #13 on: September 26, 2011, 03:59:20 AM »

I appreciate all of the comments.

A Deep Cycle battery that is "rated" at 140 Amps should never be discharged below about half of that or it will fail prematurely.  However, in an emergency you do what have to do.  I have two of these batteries so, in practical terms, I have 140 Amps at my disposal without damaging anything.

I tested my 400 watt DC to AC converter this weekend.  I took it down to 11.3 volts and the converter was still putting out 123 volts AC and this largely answered my question.  I was able to get about 24 hours of BiPap use plus some 12 volt LED lights and a very small fan.  It's recharging now.

Logged
AA4HA
Member

Posts: 1378




Ignore
« Reply #14 on: September 26, 2011, 07:37:25 AM »

Since lead-acid batteries are dependent upon a chemical reaction to generate a potential we need to remember that as a battery discharges the specific gravity of the electrolyte changes from very acidic to more basic. This means that the sulfur in the battery ends up plating out or precipitating of the solution and forming lead-sulfur compounds in the cells. Some of these compounds can be regained by charging but some end up forming a sludge in the bottom of the battery. The sludge is lead and acid that will longer contribute to the battery action.

Eventually the sludge levels can build up to the point where they short out the bottom of the battery plates leaving you with a dead cell. Under heavy discharge/charge cycles you could plot out the battery capacity over time and see how each deep discharge cycle does about the same damage as eating a pound of butter does to your heart. Capacity is reduced and while some is regained on the charge cycle it is not the same as it was when the battery was new.

The battery booster is a useful gadget to have as long as you understand that you may be buying a new battery after each field day weekend where you spent half of Sunday running a booster off of a battery that may of only had 10.5 volts capacity. When you take it home to charge it up the battery may appear to draw almost no current on the charge because the conductive electrolyte solution is weaker. It may take quite a bit more time on charge before the battery begins to charge at what would be considered a normal charge rate (so many A/hr). You may find that the battery will not hold a charge (that sludge) or that a cell shorts out.

It is all a trade-off. I would rather drag along two deep cycle boat batteries than one battery and a booster. (as long as I did not have to backpack the thing in).

If you have a lead-acid battery that has the clear or whitish colored sidewalls you can see the little pockets in the bottom of the battery where the sludge can accumulate (like snow).

Also, when enough of the metallic lead has precipitated or scaled off of the battery the cell can mechanically fail (internally) and short out, boiling all of the electrolyte out of one cell and you have a hot battery until it kills off that cell. Batteries for rough service (like a car battery) are meant to deal with vibration and have heavier metallic mesh frames that hold the lead into place.
Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!