It's small, has both voltage outputs from one package, and I can easily disconnect it for recharge (no special charger needed, just a standard 5V USB wall wart.)
Pros - low cost, single small package geometry fits available space, convenient connect/disconnect and recharge, plenty of capacity.
Cons - 5V charger port requires minimum maintained 100mA to stay "ON", 12V port is constant on and capable of 300A output if shorted.
To resolve "cons"...
A 50R resistor across the 5V output keeps the power on for the processor and relay modules. That only drains 100mA, so no problem for the planned three hour max. run time.
The 12V will be fused and switched, with max. draw of near 15A@12V. Total "ON" time at 15A about 0.3h per session....about 4.5Ah. So the 8Ah capacity is good.
Automotive batteries charge somewhere between 13.6 and 14.5(?) volts they are typically not well regulated and as mentioned could have a lot of ripple (small variations in the voltage, wither at 60Hz or 120 Hz)
Guys....thank you for the feedback. this is not a charger...its called that, but it jump starts cars. It's basically a high output LiPo battery. I should have changed the title.
It measures a steady 12.4VDC. Since a LiPO battery, should be flat DC.
The phone charger port puts out 5.12V, drops to 5.03V under max load.
I posted because of concerns on the potential 300 amp output and to see if anyone had experience with this, or an even simpler approach.
I don't know how long that relay module will last with 13amps going through it at once. Wouldn't it be better to use MOSFETs instead of relays as you're using DC. You can get them on modules and they would be more reliable than relays. You're doing a lot of on/off over time and those relays will start to drop in a matter of months. I'm guessing the power source is ok though.
Rob - max switching through a single relay is about 4A. The 13 comes from 3 relays x 4A at once and another relay at less than 1A. Not all thru same relay.
In a three hour typical run a single relays will activate maybe a max of 30 times. At only 5-10 runs per year, thats 300 cycles per year on a relay.
I like the concept but you might want to fit some suppression capacitors (say 0.1) across the relay contacts to help minimise arcing when they open. Also, don't expect to get the full 8Ah from the battery pack, manufacturer claims with respect to capacity often leave a lot to be desired.
jackrae,
Great, thank you.
Not shown in the attachment, but there are a total 18 relays...9 switching 12V,4A heater coils and 9 switching 12V, 20mA solenoid driven air valves. I have flyback (name?) diodes on the 9 solenoids.
Can/should I also put capacitors on those relays?
I'd suggest fitting them unless the relays are specified capable of carrying at least 10A DC. Note that relay contact DC ratings will usually be much less than the AC ratings. This generally applies to both voltage and current unless the relays are specifically designed for full rating at dual voltage and waveform (ie super expensive)
Relay contacts are rated 10ADC. These are seeing a max of less than 5A at any time, and very infrequent activation.
Likely will add diodes.
Thanks all.
