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Battery vs. Power Supply
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David
Not really pi relevant, but Jason suggested I put my question/issue to the group.? So here it is.
? I have an offgrid shack and power my Yaesu FT-891 from a 12Ah LiFePO4 battery that is recharged with solar panels.? I have noticed that my SSB output was dropping alarmingly. I then tested the output using RTTY, CW and AM and found the radio was only putting out 50-70w even though the battery was fully charged. To further test, I made sure the battery was fully charged (measured 14v at battery with multimeter) and attached the radio to a dummy load via a very short pigtail, with an SWR/Power meter inbetween. I used RTTY, CW, AM FM modes, all things with a continuous carrier frequency, on all amteur radio bands at various frequencies within the bands.? Again I measured only 50-70w on both the radio's SWR/power meter and the external one. I took the whole setup back to my office and attached the radio to a 13.8v power supply.? Same power cable.? Same pigtail. same SWR meter, same dummy load.? I used RTTY, CW, AM and FM on all amateur radio bands and on frequencies within the bands.? This time I measured 100w on the radio's SWR/power meter and the external one. I am at a loss to explain this.? Does anyone have an idea? Thx in advance. David SV0SGS |
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B J Greatrix
开云体育Hi, I powered my shack for many years from a 12v Lead acid truck battery. Eventually this gave up the ghost, in exactly the same way. I reckon that the batteries internal resistance was the cause as even trying to power a 15W lamp would have problems. The voltage would drop off very quickly. A new 80AHr battery solved the problem
regards Bernard
On 22/06/2021 14:38, David wrote:
Not really pi relevant, but Jason suggested I put my question/issue to the group.? So here it is. |
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David
开云体育I will try the ammeter.? This is a commercially manufactured 12Ah LifePO4 battery.? To paraphrase a blue jeans commercial, nothing comes between my battery and my radio.? Ie no buck converter or anything else.?? But maybe there is some kind of limit on the amount of amps it can deliver.? Has anyone else experienced this kind of limitation? If not, what kind of batteries (model and manufacturer) are you using??At 100W ouput, my radio draws only about 15A according to the ammeter on my power supply.? But that doesn't make any sense. 13.8V times 15A is 207W. David Am 22.06.21 um 16:47 schrieb Kevin:
Internal resistance of the Battery vs the Power Supply? |
开云体育David, Having looked into LiFePO4 batteries... Not all are the same with output current capabilities.? The current is also dependent on the BMS used. For my use I have LiFePO4 batteries purchased RAW (no BMS) and stock they can provide 100 Amps.? My "BMS" has a 65A limit and the pack is fused (CB) at 50 Amps.? I know I can provide the 25A to run a 100W rig. Looking a specks for some 12AHr and 20AHr batteries, I have noticed that some have low Amp ratings. Since you don't
get full power with the battery and you do with a power
supply, I would check the ratings of the battery and/or check
the battery.? The battery may have a bad cell? too...? I
"assume" the battery is fully charged when you tested the
rig/battery ????? Is the charge controller working properly??
73, steve WB3LGC On 6/22/21 9:38 AM, David wrote:
Not really pi relevant, but Jason suggested I put my question/issue to the group.? So here it is. |
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I’ve had the same experience with various batteries versus a stiff, well-regulated 13.8 volt power supply. As the batteries age, they develop higher internal resistance. If you can monitor the voltage across the power leads at the radio, you will see the voltage drop with increased load and an aging battery. The IC-706 I use in our camper has reduced power output even at 12.0 or 12.5 volts. I use a N8XJK Voltage Booster at the radio to maintain 13.8 volts at full load. It compensates for aging battery and voltage drops from power cable resistance between the battery and the rig.
Most solid state rigs are designed for operation at 13.8 volts, not the nominal 12.6 volts provided by lead acid batteries. The radio’s power output will decrease with the lower DC input voltage. Other battery chemistries will provide different terminal voltages depending on their cell configurations. The current drawn by your radio (15 A at 13.8 V) is typical for a 100 Watt, RF output radio. That would indicate an efficiency of around 50%, very reasonable performance for modern radios using linear solid state PA stages. 73 Mike, AI8Z |
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Thx for your reply.? 13.8V and 15A comes out to 207W.? I guess that is what your referring to with "50% efficiency"?
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David SV0SGS Am 22.06.21 um 17:35 schrieb MIKE AI8Z: I’ve had the same experience with various batteries versus a stiff, well-regulated 13.8 volt power supply. As the batteries age, they develop higher internal resistance. If you can monitor the voltage across the power leads at the radio, you will see the voltage drop with increased load and an aging battery. The IC-706 I use in our camper has reduced power output even at 12.0 or 12.5 volts. I use a N8XJK Voltage Booster at the radio to maintain 13.8 volts at full load. It compensates for aging battery and voltage drops from power cable resistance between the battery and the rig. |
开云体育Thx for your reply.? I will check the battery specs again. It has been a while. Maybe it just can't deliver the amps. It is possible that the battery could have developed a bad cell, but I don't think that is likely, as it charges to full capacity and is quite new.? The battery was fully charged (~14V) when I did my tests.? Power cable is very short.? I use a Genasun MPPT charge controller.? It has a good reputation.? I will disconnect it from the fully charged battery and test again.I will be upgrading my batteries, solar panels and charge controller in the near future.? As Tim Taylor was fond of saying, "More power!"? Maybe I will have then the output I would like to have. I live on a small Greek island in the Aegean Sea.? I am surrounded by salt water.? My antennas are located about 150 meters above sea level.? I am amazed and quite pleased sometimes at the SSB contacts I make with "only" 50-70 watts of power.? It is even more pleasing when I have a QSO with someone who is also doing portable, low power, not necessarily QRP. I am kind of portable, inasmuch nothing is permanently installed, and I can take my stuff on my motor scooter to another location.? The island is small, so there is really no point from a radio standpoint, to go anywhere else.? I operate out of my olive grove. Vy 73! David SV0SGS Am 22.06.21 um 17:13 schrieb stephen
shearer:
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开云体育Hi, Steve!Thx for your reply.? I will check the battery specs again. It has been a while. Maybe it just can't deliver the amps. It is possible that the battery could have developed a bad cell, but I don't think that is likely, as it charges to full capacity and is quite new.? The battery was fully charged (~14V) when I did my tests.? Power cable is very short.? I use a Genasun 10A MPPT charge controller.? It has a good reputation.? I will disconnect it from the fully charged battery and test again. I will be upgrading my batteries, solar panels and charge controller in the near future.? As Tim Taylor was fond of saying, "More power!"? Maybe then I will have the output I would like to have. I live on a small Greek island in the Aegean Sea.? I am surrounded by salt water.? My antennas are located about 150 meters above sea level.? I am amazed and quite pleased sometimes at the SSB contacts I make with "only" 50-70 watts of power.? It is even more pleasing when I have a QSO with someone who is also doing portable, low power, not necessarily QRP. I am kind of portable, inasmuch nothing is permanently installed, and I can take my stuff on my motor scooter to another location.? The island is small, so there is really no point from a radio standpoint, to go anywhere else.? I operate out of my olive grove. Vy 73! David SV0SGS Am 22.06.21 um 17:13 schrieb stephen
shearer:
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开云体育David, yes the
Genasum are good units.? 14V IS full charge.? QRP is fun
too...? I am often amazed what it will do.? steve WB3LGC On 6/22/21 12:17 PM, David via
groups.io wrote:
Thx for your reply.?? |
开云体育Hi, Bernhard!Thanks for writing.? I will be upgrading my batteries and photovoltaic system in the near future and look forward to 100W output. Vy 73 David SV0SGS Am 22.06.21 um 16:59 schrieb B J
Greatrix via groups.io:
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I use an MFJ-446C Battery Booster to keep the transmitter at 13.8 Volts up to 25 amps. Booster drops out on receive so no noise issue controlled by xcvr PTT or manually. Input can be set to shutdown when available battery voltage under load drops to 9, 10 or 11 volts depending on placement of a jumper.
Bill AF4B |
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Ed, KD8YQQ
There are a number of possible factors involved here that will cause this when using a battery vs a power supply.
Like most mobiles, the Yaesu FT-891 will roll back the output power whenever the input voltage drops and it will try to find a "happy" medium between the input power and what it will allow on the output, this helps in preventing the finals from overheating.? ? In your case, powering the radio with a 12AH battery indicates that the battery is under a 1.25C load current in order to output 15 amps for 100W RF output.? ?As you increase the discharge rate, also known as C Rate,? of a battery, the internal resistance has more of an impact on the voltage drop.? In contrast, a heavy duty lead acid truck battery, is likely rated around 105AH or more of "reserve" capacity.? In this instance, a 15 amp load will create only a? 0.14C discharge rate on the battery, so the voltage drop when the MIC is keyed will be significantly less, which is why you did not see this before.? With the smaller voltage drop, the Yaesu did not attempt to fold back the output power. This may be more detailed of an explanation then you were? looking for, but it is early morning, I have had too much coffee, and felt like typing :) Anyway here are some suggestions... #1 - The Lithium Battery you are using is undersized to hold the voltage the radio looks for when running at 100W, if? your wallet allows it, consider going to a larger lithium in order to minimize the voltage drop.? If I were to guess, I would say a 75AH or higher Battery, however this may be an expensive route. #2 - The MFJ Battery Booster will regulate the voltage to the radio and get you 100W for a while by pulling some additional current from the battery.? However, you battery is still undersized and the battery booster will drive it even harder as it tries to compensate for the voltage loss.? This may not be a good path if you plan to do a lot of TX'ing.? #3 - If the cost get's too crazy, consider going back to a Heavy Duty Truck battery, it will likely be your cheapest option.? ? #4 - Just to throw it in there, make sure you are using 12 Gauge or larger wiring between the radio and the battery.? If it is a long distance between the radio and battery, consider 10 gauge or larger. ? Ed - KD8YQQ |
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I agree with Ed.. I am curious if the lifepo4 battery was giving 100w RF power in the past or never did? If not then you can parallel in more battery and save a little $. if it did give more power then there maybe some deterioration of the battery but "a bad cell" should show up as a drop in voltage of around 3.2volts..? your asking too much of that battery on transmit IMHO
73 KD9MDL? |
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I also agree with Ed, especially regarding the C rating of your LiFEPO4 batteries. I built a solar generator based on Julian’s (OH8STN) 576W design and when researching this chemistry I found there was a wide range of C values, which tells the amperage that the cells can put out. It would be interesting to see what your cells’ C rating is.
BTW, operating in an olive grove surrounded by salt water sounds like a very pleasant operating environment! Jay 73 de N0SR? |
开云体育Thank you to everyone who has given me advice on this issue.? I have gotten great lessons in battery chemistry and management.? I also realize too that I had greater expectations on my battery than it could deliver.? I am planning an upgrade of my photovoltaic system including batteries with greater capacity. So I expect that will get my TX up to 100w.? I don't plan on running an afterburner, aka amplifier, figuring I can compensate for more power (sorry, Tim Taylor) with my location (high, surrounded by salt water) and? good antennas.?I am one of two radio amateurs on the island.? The one has a "super station" but is 100% dependent on the grid.? I prefer to work portable and off grid.? One never knows if and for how long the electricity will be cut off here.? No APRS activity here, but I do have some good (PAT) Winlink connections up in Switzerand and Germany so I can get information out and receive it.? Not many people here are impressed with the communications possibilities of amateur radio.? Too into internet and 3g/4g/5g cellphone service, I guess. Vy 73 to all Ops! David SV0SGS ?23.06.21 um 19:45 schrieb JaySheepdog: I also agree with Ed, especially regarding the C rating of your LiFEPO4 batteries. I built a solar generator based on Julian’s (OH8STN) 576W design and when researching this chemistry I found there was a wide range of C values, which tells the amperage that the cells can put out. It would be interesting to see what your cells’ C rating is. |
MIKE AI8Z
Bill Lamm
JaySheepdog
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