|
Bruce,
?
I do encourage people to know what they are doing.
It's good we have this conversation to alert them of the dangers of large batteries.
?
Most of us think nothing of barrelling down the road at 70mph wrapped up in a steel cocoon
with 15 gallons of gasoline and a lead acid battery.? A battery protected by automotive fuses.
That's considerably more dangerous than anything we've discussed here.
?
I'm sure many in the forum have a lead acid battery sitting under the desk for backup power.
An LiFePO4 battery is a better choice, for both safety and performance.
I remain convinced that an automotive fuse inline with 16awg wire is sufficient
to safely power a QMX from a large 12v battery.
?
Jerry, KE7ER
?
?
?
?
Let's not get too carried away with special $150 fuses and such, that only discourages the use of these batteries.
Large high current batteries should be treated with respect, but are very useful for the amateur.
Used properly and with some understanding of what's going on, they are not dangerous.
Jerry.?
To save you any more Arc welding experiments :? The maximum breaking capacity I've ever seen quoted for ATO fuses is 1kA at 32V..? ? Which is a lot ... surprisingly so . . but in some cases, close to a battery,? not enough..
For the record I really cannot agree that safety should be put aside to encourage those less experienced (aka no idea 'what's going on') to use large battery storage without proper protective devices but it's up to you for you I guess.?
As I was saying the T fuses are the expensive way to do it properly and it's already identified that there are several better cheaper ones that also do the job safely and properly and/or even better.?
|
Let's not get too carried away with special $150 fuses and such, that only discourages the use of these batteries.
Large high current batteries should be treated with respect, but are very useful for the amateur.
Used properly and with some understanding of what's going on, they are not dangerous.
Jerry.?
To save you any more Arc welding experiments :? The maximum breaking capacity I've ever seen quoted for ATO fuses is 1kA at 32V..? ? Which is a lot ... surprisingly so . . but in some cases, close to a battery,? not enough..
For the record I really cannot agree that safety should be put aside to encourage those less experienced (aka no idea 'what's going on') to use large battery storage without proper protective devices but it's up to you for you I guess.?
As I was saying the T fuses are the expensive way to do it properly and it's already identified that there are several better cheaper ones that also do the job safely and properly and/or even better.?
|
Let's not get too carried away with special $150 fuses and such, that only discourages the use of these batteries.
Large high current batteries should be treated with respect, but are very useful for the amateur.
Used properly and with some understanding of what's going on, they are not dangerous.
Far less dangerous than the 2000 kV plate supplies of an old school transmitter.
?
My advice for powering a QMX is to just use something like16 AWG wire, not 0000 welding cable.
16 AWG is 0.004 ohms/ft, so 6 ft of wire round trip is 0.024 Ohms, at 1A that's only 0.024 of voltage drop.
A 2A automotive fuse in the power supply wires is fine, and the wire will go if the fuse does not for some reason.
Try not to drop a screwdriver across the battery terminals.
?
As an experiment, I donned my safety goggles and shorted out our 30kwh 48v off-grid battery bank
using two feet of 6 AWG copper wire and a 7.5A ATO automotive fuse, curious if the fuse would arc over.
It did not, just a nice pop and flash of light inside the fuse.
I am not confident that this would always be the case for a 48v supply, for example this may depend
on how large a gap gets established by the initial current surge, or who made the fuse.
I am confident that such an automotive fuse is adequate for a 12v supply.
After all, a lead-acid starting battery can also deliver several thousand amps when shorted.
?
Here's a quick video that drives home why we care about high voltage DC arcs.
https://www.youtube.com/watch?v=Zez2r1RPpWY
The AC arc self quenches whenever the sine wave crosses zero volts, at 60Hz*2 = 120 times per second.
The DC arc has no such quenching action, the ionized air in the arc remains conducting till the arc is quite long.
In this case it's 240 Volts DC, not 12 Volts.
?
LiFePO4 is a very good choice.
Safer than most other lithium chemistries, and has reasonably good power density.
A 100AH battery is good for half a week with key down at 5W out on a QMX.
Excellent for emergency backup communications.
?
Jerry, KE7ER
?
?
On Mon, Apr 14, 2025 at 07:52 AM, Bruce Akhurst wrote:
?
On Thu, Apr 10, 2025 at 02:52 PM, Bruce Akhurst wrote:
Hope you’ve got your fault protection sorted.?
Prospective short circuit will be 10kA and an auto fuse ain’t going to stop that arcing ..
It can be as simple as a fusible link.? Go down 4 wire size numbers, so for example #16AWG link in #12AWG conductor, a foot long, connected in series with the main 12AWG line with compression crimp splices NOT solder.?
The link including splices and at least an inch beyond (I cover about 2-3 inches), is covered with fire sleeve.?
I use an 18 inch long sleeve for a 12 inch link; the idea is to contain and cool the hot gases if the link fuses so leave room
Exactly.? ?I see a lot of DIY/ RV stuff where 100's of Ah of lithium batteries are merrily connected to quite low consumption projects in inflammable locations without properly thinking through the prospective fault/short circuit currents and consequences.? ?
Large current DC arcs are hot and self sustaining and something you only want to see once and not in your workshop /office /Van/ home.?
In theory the better batteries may have BMS or other internal protection but it's hard to test that without damaging the battery and it may not be there or not reliable anyway.? ?
T grade fuses are $150 for a high interrupting current fuse+holder so cheaper alternatives are useful.? ? ? ?
Also don't ignore marine grade Switch/Breakers which are resettable, re-usable? and decent ones by Buss etc (no not ebay clone/copy ones) can typically carry and switch 15 - 100A or more as circuit breakers and interrupt 6000 amps in fault conditions for less money than a T fuse . .??
Note a 'battery switch' or 'breaker' or 'resettable fuse' while cheaper,? are not necessarily able to interrupt large DC fault currents and this figure usually missing from their specs?
Bruce
|
?
On Thu, Apr 10, 2025 at 02:52 PM, Bruce Akhurst wrote:
Hope you’ve got your fault protection sorted.?
Prospective short circuit will be 10kA and an auto fuse ain’t going to stop that arcing ..
It can be as simple as a fusible link.? Go down 4 wire size numbers, so for example #16AWG link in #12AWG conductor, a foot long, connected in series with the main 12AWG line with compression crimp splices NOT solder.?
The link including splices and at least an inch beyond (I cover about 2-3 inches), is covered with fire sleeve.?
I use an 18 inch long sleeve for a 12 inch link; the idea is to contain and cool the hot gases if the link fuses so leave room
Exactly.? ?I see a lot of DIY/ RV stuff where 100's of Ah of lithium batteries are merrily connected to quite low consumption projects in inflammable locations without properly thinking through the prospective fault/short circuit currents and consequences.? ?
Large current DC arcs are hot and self sustaining and something you only want to see once and not in your workshop /office /Van/ home.?
In theory the better batteries may have BMS or other internal protection but it's hard to test that without damaging the battery and it may not be there or not reliable anyway.? ?
T grade fuses are $150 for a high interrupting current fuse+holder so cheaper alternatives are useful.? ? ? ?
Also don't ignore marine grade Switch/Breakers which are resettable, re-usable? and decent ones by Buss etc (no not ebay clone/copy ones) can typically carry and switch 15 - 100A or more as circuit breakers and interrupt 6000 amps in fault conditions for less money than a T fuse . .??
Note a 'battery switch' or 'breaker' or 'resettable fuse' while cheaper,? are not necessarily able to interrupt large DC fault currents and this figure usually missing from their specs?
Bruce
|
Most buck converters already have such capacitors, but they are definitely needed with the 78xx linear regulators.?
|
On Sun, Apr 13, 2025 at 09:00 PM, Braden Glett wrote:
Where do you place the 100 pf caps?
Right across the input and output DC connections; noise can be conducted/radiated from the input as well as the output; control lines, too.
At less than a dime apiece for chip caps I am pretty liberal with their use, I am a belt-and-suspenders kind of guy.??
73, Don N2VGU
|
Hello Don,
Thank you for the added information! Although, as I had said, I detect no noise from the Drok, I'm sure someone reading this thread will find your tip to be invaluable.?
Where do you place the 100 pf caps? Across the output (+ and -) leads of the regulator output? Somewhere else?
73
Braden Glett KD8ZM?
|
On Sat, Apr 12, 2025 at 08:41 AM, Braden Glett wrote:
I live on a 20 acre horse ranch where there is absolutely no neighborhood RF noise, and even in that low-noise environment, I cannot detect any noise from the Drok.
I keep a supply of 100pF and 1000pF NP0 leaded capacitors handy.? It only takes a second to tack-solder a couple onto a board or slip them into terminal block connections to help with RF bypassing power supply outputs.
It is easy to add leads to chip caps, which is essentially what the epoxy-dipped caps are, if that's what you've got.
73, Don N2VGU
|
Jerry, thank you. That helps a lot. I live on a 20 acre horse ranch where there is absolutely no neighborhood RF noise, and even in that low-noise environment, I cannot detect any noise from the Drok. I can't take credit for choosing the Drok, someone on this forum suggested it as a good regulatory to use, and they were correct, apparently!
Thanks again and 73!
Braden Glett KD8ZM?
|
On Thu, Apr 10, 2025 at 02:52 PM, Bruce Akhurst wrote:
Hope you’ve got your fault protection sorted.?
Prospective short circuit will be 10kA and an auto fuse ain’t going to stop that arcing ..
It can be as simple as a fusible link.? Go down 4 wire size numbers, so for example #16AWG link in #12AWG conductor, a foot long, connected in series with the main 12AWG line with compression crimp splices NOT solder.?
The link including splices and at least an inch beyond (I cover about 2-3 inches), is covered with fire sleeve.?
I use an 18 inch long sleeve for a 12 inch link; the idea is to contain and cool the hot gases if the link fuses so leave room.? Close each end of the sleeve with a zip tie or flat lacing tape.? Extra style points for two ties 1/2 inch apart.
?
More folks should be aware of the advantages of lacing tape over zip ties in applications like this, especially where someone has cut the zip tie surplus with a diagonal cutter, leaving two flesh-shredding hooks exposed.? A tool like this will properly tension and cut the tie with a blunt end, save time and avoid much bloodshed: ?
Lacing tape:
?
Of course an appropriate fuse is generally needed to protect against nuisance overloads as well; they are easier to replace than a link.
?
Let's be safe out there.
73, Don N2VGU
?
?
?
?
?
?
|
Braden,
?
Tisha is saying that linear regulators burn the difference between Vin and Vout as heat.
Your DROK is a switcher, not a linear regulators, that's a good solution if it doesn't create too much noise.
About half of the posts in this thread are about linear regulators.
?
Tisha's advice on linear regulators is good.
1)? Linear regulators should have caps on input and output to keep them stable, or they may oscillate and cause noise.
2)? Also check the datasheet for the dropout voltage, some require that Vin be a couple volts greater than Vout.
?
Some linear regulators have a dropout of less than half a volt.
?
Don ND6T descripted an effectively zero dropout circuit he had seen in SPRAT:
?
Jerry, KE7ER
?
?
?
On Fri, Apr 11, 2025 at 04:02 PM, Braden Glett wrote:
Tisha,
I wanted to make sure I'm understanding what you are saying.
As stated earlier, I am using a Drok to regulate from a 12v LiFePo Bienno 3 Ah (actually 13v as I measure it), down to 11.9v. I hear you saying I might be losing more in heat from the Drok than the rig is putting out in power when transmitting (a lot more, in fact!). Yet, I don't feel any detectable heat coming from the Drok.
Is there something I've misunderstood?
TY 73
Braden Glett KD8ZM?
|
IF you getting noise form 78xx parts its your fault.
?
The input need minimally 1uf cap with short leads and the
output not less than .1uf.? ?The 78xx part are linear regulators
and if there is noise its because the bypassing is poor and
its oscillating.
?
I've seen that in many cases, used wrong it does bad things.
?
--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.
|
Tisha,
I wanted to make sure I'm understanding what you are saying.
As stated earlier, I am using a Drok to regulate from a 12v LiFePo Bienno 3 Ah (actually 13v as I measure it), down to 11.9v. I hear you saying I might be losing more in heat from the Drok than the rig is putting out in power when transmitting (a lot more, in fact!). Yet, I don't feel any detectable heat coming from the Drok.
Is there something I've misunderstood?
TY 73
Braden Glett KD8ZM?
|
The suggestion on adding a low value (100-1000 pF) capacitor in parallel with the 20-1000 uF bypass capacitors if the best answer. It has to do with the frequency response of the capacitors and their ability to nibble away at the high frequency component.
?
With linear regulators you need to have a few volts higher on the input when compared to the output so the regulator has something to regulate and drop voltage. Not too much because that voltage drop during regulation is converted to heat. For example; If you had a 18 volt input and a 12 volt regulated output at 2 amps that 6 volts of drop, multiplied by 2 amps would be 12 watts of (thermal) that would need a substantial heat sink to dissipate.
?
The other way is bad too, a 12 volt regulator with a 12.5 volt supply. The 78xx series regulates best when the input voltage is > ~2.5V up to ~10V. Below that differential and the regulator cannot function correctly and you would be better off with just a diode string.
--
Tisha Hayes
AA4HA
|
On Fri, Apr 11, 2025 at 08:22 AM, Richard Barnich wrote:
The 78/79 hundred families of regulators expect bypassing on both input and output sides of the regulator.
I always parallel a 100- or 1000pF cap with the bulk bypass for additional RF bypassing/filtering.? Those larger values do not work effectively at higher frequencies.
73, Don N2VGU
|
I am using a Drok buck converter from Amazon. DROK DC Buck Converter:
It works great, and no noise. I set it at 11.9 volts and just leave it there. I put anderson powerpole connectors on each side input and output: https://www.amazon.com/dp/B0CNZ1V5CL?ref=ppx_pop_mob_ap_share
I predict you will like this solution.
73
Braden Glett KD8ZM?
|
The 78/79 hundred families of regulators expect bypassing on both input and output sides of the regulator.Look at the data sheet for recommended values. Typically, 3.3uf and 0.1 or 0.01uf on the output. Short lead lengths are also recommended. without these, stray inductance is going to cause the regulators to oscillate.
Rick K8BMA
?
|
I used 7812 and there was slight noise. I returned to one diod instead and everything is ok now. 09:32, 11 April 2025, "Alan G4ZFQ via groups.io" <alan4alan@...>:
On 10/04/2025 18:28, Petrov Sergey via groups.io wrote:
?It generates slight RF noize. Which is annoying.
Do you mean the 7809 is producing RF noise?
If so, then suspect the decoupling capacitors.
A 7809 should be noise-free.
73 Alan G4ZFQ
--
Sent from Yandex?Mail for mobile
|
On 10/04/2025 18:28, Petrov Sergey via groups.io wrote: It generates slight RF noize. Which is annoying. Do you mean the 7809 is producing RF noise? If so, then suspect the decoupling capacitors. A 7809 should be noise-free. 73 Alan G4ZFQ
|
Hope you’ve got your fault protection sorted.?
Prospective short circuit will be 10kA and an auto fuse ain’t going to stop that arcing ..
|
Bruce Akhurst
Donald S Brant Jr
Braden Glett
Tisha Hayes, AA4HA