Can you show us the other side of the drive? Curious what make/model this is supposed to be. Best guess is that this is yet another attempt by a PC manufacturer to sell un-upgradeable units that need to be either replaced as a whole, services only by then, or had at with wire snips and a soldering iron.
I’d say it’s time to carefully cut out that tab (leaving the keys intact), and to start being more careful about what you buy.
The relay will cause a short voltage drop when switching. This could be a problem if your circuit can’t handle a short voltage drop.
Probably the Mean Well has adjustable output voltage. If you can trim the output voltage of the power supply to a higher voltage than your battery, then you can probably just run each power source through a diode and merge them after the diodes.
note that if you do have issues with the voltage fluctuating when the relay switches, you can often connect a ceramic capacitor across the coil contacts of ~1uF along with a small diode acting as a flyback connected in reverse polarity, and it’s enough to smooth out a good bit of that draw and/or switch-off flux pulse. Filtering saves lives
Thanks, I don’t think there are any external settings for the power supply, but it does provide a few more volts than I strictly need. Toggling a single relay hasn’t caused me any issues in the limited testing I’ve done. A momentary drop to as low as 5V should be perfectly fine, although, looking over the specs for my components, I see I’m getting dangerously close to the upper limits for the power supply’s current rating. I’ll have to look into connecting 2 supplies in parallel (or getting a larger supply) I suppose.
I haven’t worked with battery backups yet, so I was thinking it would be best to keep that element simple to minimize potential issues like a trickle charge draining the battery unexpectedly, or damaging the battery from overcharge. The minimum requirement is just to ensure the hardware (a motorized ball valve) returns to a closed position if power is lost. The battery needs to provide at least 9V to power the motor, so I could use a 9V (or a few smaller cells in series) to keep it below the 12V supply.
With your solution using a diode on each voltage source, would there be any risk of a trickle charge draining the battery unexpectedly if the battery? If so, in that configuration I’d need to do more research and figure out how to use a BMS, rather than an externally recharged or disposable cell.
With your solution using a diode on each voltage source, would there be any risk of a trickle charge draining the battery unexpectedly if the battery?
Current flows from high to low voltage, but the battery is at a lower voltage than the supply. Check the diode’s datasheet for the reverse current at the voltage that would be across it. It should be negligible
Unless otherwise specified at certain loads, relay duty cycles are always 100%.
Most relay duty cycles are in relation to switching currents, not the coil operation. There is always a slight resistance between dissimilar contacts, and carrying current across the contacts creates heat, so they have a max rated current for continuous use. They can often exceed this, but only for short periods before needing a duty cycle cooldown.
When the relay switches high near-max currents, especially in DC, it generates a large arc across the contacts. This makes them heat up. This limits the actuation frequency because too many arcs at max/overcurrent will overheat the contacts and could cause them to fuse together.
But the coil itself is designed such that it will never overheat on it’s own just from the trigger voltage. Granted it’ll waste a lot of power to resistive heating that is undesirable if your goal is power efficiency, but it will be perfectly OK.
I’m a little new to the terminology, so to clarify, the switching current refers to the amperage across the terminals other than the coil, right? I’m definitely within those limits; I don’t expect to transfer more than ~1/8 of the maximum amperage.
Is there a rule of thumb for the minimum current I should allow across the coil? The only specification I see on the datasheet for coil amperage is that it was tested to failure at 100mA. I don’t think power consumption is too big of a deal with this use case, but resistive heating sounds like it could shorten component life (and even if it’s only a secondary consideration here, I’d still prefer to minimize waste).
the switching current refers to the amperage across the terminals other than the coil
Yes. “Switching current” is the load current being controlled across the main contacts. I figured you were well within specs, I was just clarifying what typically limits relay duty cycle other than the coil.
Is there a rule of thumb for the minimum current I should allow across the coil?
Stick to the rated coil voltage in the datasheet or below and you’ll be fine. They set the coil resistance to be within the safe current zone per V=IR at rated control voltage.
Many relays can reliably switch well underneath their rated control voltage depending on their design- there’s a lot of safety factor built in. I’ve had some 12v automotive relays switch successfully at around 5v (by accident, lol). Experiment a bit and you may be able to cut down on waste power
Just be aware that control voltage (coil) and rated switching voltage (load) is often different, since many relays use low control voltages to switch high voltage loads. Don’t confuse the two!
Thanks, that’s good to know! The datasheet doesn’t seem to include the word “duty” anywhere, so I think that must have been omitted. Ostensibly that means the maximum duty cycle is unlimited, but I don’t have enough experience here to say that with any confidence.
Just about any soldering iron should work. Chisel tips are better than round tips for most work. I really like J tips as well, they’ve got a range of usable surface sizes without having to change tip just by turning the iron around.
Put a piece of heat shrink tubing on one wire.
Strip the ends, and form a Western Union splice in the wires to hold them.
Set the iron to 350°C, and let it heat up. If your iron doesn’t have temperature control, it’s cheap crap and should probably just be thrown in the trash since it’ll tend to over-heat and lift pads when soldering PCBs. Continue for now, that doesn’t matter as much for soldering wires.
Then apply a tiny bit of solder to the tip of the iron so that it can make good contact, apply flux to the bit where the wires join (do NOT skip flux), touch the solder to the wires, and then touch the iron to the other side of the wires. The solder should quickly melt & flow into the joint.
Remove the solder, then remove the iron.
Let the joint cool, then slide the heat shrink up over the joint and shrink it with a heat gun.
Crimp connectors tend to be stronger and more vibration-proof than solder, but sometimes space constraints mean that soldered splices are necessary. Also crimpers are expensive, for many wire-to-wire crimp families the official crimpers are several hundred dollars.
Sixfab uses the Telit ME910C1-WW chip on some of their USB models and the Quectel EC25-A for others. They are available as M2 form factor inserts, or you can buy just the chip.
Thanks for the input. I had already looked up the EC25 which is based on the same Qualcomm chip and a tad larger than the L6, but am unfamiliar with Sixfab and the telit chip you mentioned. I’ll look them up more. Cheers.
Edit: the Telit chip is 28x28mm and is LTE UE Cat-M1 with 1Mbps up/down from what I understand. Does not seem to offer LTE cat 4 speeds.
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