figured it out *
It is called a relay. Have questions about relays in comments
original:
hello all,
I am going to have two separate battery packs connected to the same circuit, however, they need to be charged separately. I was wondering if there is a programmable “railroad switch” device that can suffice this. Lets disregard how the batteries are being charged for simplicity. Battery pack 1(lithium ion batteries) has charge priority. Therefore, when the energy is coming it charges battery pack 1 only! When battery pack one is completely charged, I want the “railroad switch” to go Battery pack 2’s circuit. Battery pack 2 is a normal car battery that is running all the time. So there is no max charge.
Is there a railroad switch” device that I have never heard of?
Or am I totally off, but there is a clever way of doing this.
I would like this railroad switch to be programmable.
Links appreciated
thank you raschemmel, that is exactly it. I just am not aware of many EE devices, although I figured this one existed. do you know if I can track the current of the Li-ion battery( because when li-ion batteries are fully charge (within ~-5%) the current drops to almost 0. So in a program when the current drops, I can relay the energy to start charging the second battery(12v car battery). Is this feasible? any tips?
You need to know the CURRENT rating before you can order a relay.
What is the MAXIMUM load current to be switched ?
What is the charging current ?
If you get one of these you can measure the voltage drop across it and
divide by 0.05 ohms to get the current . (ICHARGING=VCSR/RCSR
and PDISSIPATED=VCSR*ICSR Where | "CSR" = current sense resistor
Put it in series between the charger and the Lithium Ion battery to measure charging current.
when the voltage drops by more than 25% or 30% then switch the relay.
You can use an LT1215 to make an Instrumentation Amplifier (see schematic on page-1 of datasheet) to amplify the voltage across the CSR. (+Vin is the positive side of the resistor and -Vin is
the negative side of the resistor)
Wow thank you. I just learned so much from that fantastic explanation. I will post in this thread again when I have answers to some of those questions. I am very happy that my idea of this schematic is reasonable thanks to you!
working on finding the current specs you asked for, but in the meant time, is there anyway I can measure the current from the lithium ion pack in real time? because when the current drops in the battery pack(indicating the lithium ion pack is fully charged. That is when I want the programmable relay(depends on what size) to charge the 12V car battery. Does this make sense? So I want real time current data to "control" the switch
Happy 100th post btw
Also, I just saw that you showed me how to measure current in real time. Thank you
raschemmel:
Put it in series between the charger and the Lithium Ion battery to measure charging current.
when the voltage drops by more than 25% or 30% then switch the relay.
also, I am not an EE so can you explain why you need those equations a little broader? of course I have seen those formulas before, but I am a little confused on what you calculated there. Thanks.
Again, still working on getting the current ratings.
I don't want to answer your question because you didn't post a schematic. I don't know if what you put in your text description is what it means to me.
Draw a schematic and I will answer your question.
The current sense resistor can go anywhere in series with the Li-on battery.
If you don't have the resistor then you can use a DMM if the current is less than 10A.
Do you have a DMM ?
Do you know how to measure current with a DMM ?
I will work on drawing out the schematic and posting it. I have a DMM, the thing is I want the programmable relay to be able to read this data(1) so it knows when to switch. So, I don't think a DMM will work. I can buy the resistor.
(1) Data - The measurement of current going to the lithium ion batteries. As the batterys begin to charge more and more the current drops. Once the current is 3-5% of its original status, I want the relay to switch.
Just to imagine, this link has a decent schematic. Although, I am going to put the 12V on the other side of the relay, and use a power source in my school's lab to power it, because I am using DC coming in. This way, I can control the maximum input voltage. Do you have any suggestions for relays that replicate electric scooter current??