Battery switching without tears

While I am reading these posts with interest, I confess to being an electrical illiterate. I just use two batteries, each with a fuse, and two switches. When switching, I turn on #2 before turning off #1.

If these circuits with diodes, resistors, make-before-break switches and so on are superior, please explain why, and if the case is compelling, a circuit diagram would be appreciated so that I might take advantage of the information.

After all, in aviation "R & D" actually stands for "Ripoff and Duplicate."

Your procedure generally works, but while both batteries are connected, battery #2 will be recharging battery #1 and powering your panel, so there's a chance you could blow the fuse on battery #2. That leaves you to finish your flight with only one nearly depleted battery.

Cheers,
...david


On Wednesday, April 15, 2020 at 9:18:08 AM UTC-4, wrote:
While I am reading these posts with interest, I confess to being an electrical illiterate. I just use two batteries, each with a fuse, and two switches. When switching, I turn on #2 before turning off #1.

If these circuits with diodes, resistors, make-before-break switches and so on are superior, please explain why, and if the case is compelling, a circuit diagram would be appreciated so that I might take advantage of the information.

After all, in aviation "R & D" actually stands for "Ripoff and Duplicate."

David- Thanks for the advice. However, I rarely have both battery switches ON for more than a second. Is this still a potential problem? I can add diodes if necessary.

No, two similar batteries have virtually no ability to cross charge like
that. People take introductory EE classes, learn about ideal voltage
sources, and assume batteries are like that. They're not.

Years ago, in a previous incantation of this same discussion, I
suggested someone take a charged and discharged battery, connect them
through an ammeter, and report the results. They did, and couldn't even
see a flicker of the needle. They concluded that ampere hours of charge
had instantly transferred from one battery to the other, before the
needle had a chance to twitch. I pointed out the ammeter would be
nothing more than a smoking hole in the table if that were true.

Mark can use his procedure if he wants, or better yet just keep both
switches on an forget about flipping switches. Unless he's a former 747
captain, who likes to fiddle with lots of switches.

Dave

P.S. Assumes batteries of the same chemistry



On 4/15/20 8:38 AM, David S wrote:
Your procedure generally works, but while both batteries are connected, battery #2 will be recharging battery #1 and powering your panel, so there's a chance you could blow the fuse on battery #2. That leaves you to finish your flight with only one nearly depleted battery.

Cheers,
...david


On Wednesday, April 15, 2020 at 9:18:08 AM UTC-4, wrote:
While I am reading these posts with interest, I confess to being an electrical illiterate. I just use two batteries, each with a fuse, and two switches. When switching, I turn on #2 before turning off #1.

If these circuits with diodes, resistors, make-before-break switches and so on are superior, please explain why, and if the case is compelling, a circuit diagram would be appreciated so that I might take advantage of the information.

After all, in aviation "R & D" actually stands for "Ripoff and Duplicate."

Unless he's a former 747 captain, who likes to fiddle with lots of switches.

Thanks for that advice, also. It's pretty much what I suspected. But, while I don't mind flipping switches, some people tell me I am better at pushing their buttons.

If you run with both batteries connected, a failure that should have blown one battery fuse with either blow both fuses or none at all. Both results are bad.

Cheers,
...david


On Wednesday, April 15, 2020 at 11:04:01 AM UTC-4, kinsell wrote:
Mark can use his procedure if he wants, or better yet just keep both
switches on an forget about flipping switches. Unless he's a former 747
captain, who likes to fiddle with lots of switches.

On Wednesday, April 15, 2020 at 8:04:01 AM UTC-7, kinsell wrote:
No, two similar batteries have virtually no ability to cross charge like
that. People take introductory EE classes, learn about ideal voltage
sources, and assume batteries are like that. They're not.

Years ago, in a previous incantation of this same discussion, I
suggested someone take a charged and discharged battery, connect them
through an ammeter, and report the results. They did, and couldn't even
see a flicker of the needle. They concluded that ampere hours of charge
had instantly transferred from one battery to the other, before the
needle had a chance to twitch. I pointed out the ammeter would be
nothing more than a smoking hole in the table if that were true.

Mark can use his procedure if he wants, or better yet just keep both
switches on an forget about flipping switches. Unless he's a former 747
captain, who likes to fiddle with lots of switches.

Dave

P.S. Assumes batteries of the same chemistry



On 4/15/20 8:38 AM, David S wrote:
Your procedure generally works, but while both batteries are connected, battery #2 will be recharging battery #1 and powering your panel, so there's a chance you could blow the fuse on battery #2. That leaves you to finish your flight with only one nearly depleted battery.

Cheers,
...david


On Wednesday, April 15, 2020 at 9:18:08 AM UTC-4, wrote:
While I am reading these posts with interest, I confess to being an electrical illiterate. I just use two batteries, each with a fuse, and two switches. When switching, I turn on #2 before turning off #1.

If these circuits with diodes, resistors, make-before-break switches and so on are superior, please explain why, and if the case is compelling, a circuit diagram would be appreciated so that I might take advantage of the information.

After all, in aviation "R & D" actually stands for "Ripoff and Duplicate."


You need to retake EE101 - if you EVER took it. Your ammeter's bandwidth (do you even know what "bandwidth" means?) WILL NOT remotely see the current flow - it just can't mechanically respond to the very short current pulse.

On Wednesday, April 15, 2020 at 10:38:25 AM UTC-4, David S wrote:
Your procedure generally works, but while both batteries are connected, battery #2 will be recharging battery #1 and powering your panel, so there's a chance you could blow the fuse on battery #2. That leaves you to finish your flight with only one nearly depleted battery.

Cheers,
...david


On Wednesday, April 15, 2020 at 9:18:08 AM UTC-4, wrote:
While I am reading these posts with interest, I confess to being an electrical illiterate. I just use two batteries, each with a fuse, and two switches. When switching, I turn on #2 before turning off #1.

If these circuits with diodes, resistors, make-before-break switches and so on are superior, please explain why, and if the case is compelling, a circuit diagram would be appreciated so that I might take advantage of the information.

After all, in aviation "R & D" actually stands for "Ripoff and Duplicate."

I have been doing this for more than 30 years and have never blown a fuse or had any adverse effect.
UH

I got so mad the last time we fought this battery switching battle, I went out and hooked a fresh 12v battery to a low 10v battery with the parallel circuit completed with an amp-meter! I saw no spike and only 300m/a current flow as the fresh battery tried to charge the low battery.........the switches didn’t melt, the amp-meter didn’t explode and the fuses didn’t blow!
I have recently solved the issue by only using one battery............15a/h lithium iron battery............have t seen voltage below 12.2 v, even after 4 hours at 2a average current flow!
Please don’t stop arguing this issue, it’s so entertaining to watch the EE’s chase imaginary amps around!
JJ

OK JJ or 9B so if I only want to keep the powerflarm running when switching to bat 2 what size cap and diode do I put in the +12vdc line to the powerflarm and does the cap go in series in the +12 line? or across the +12 -12 or ground?

CH