BS2 as vehicle battery isolator controller
Spere
Posts: 9
I have a couple BS2s floating about from various other projects and would like to use them to setup a 'smart' vehicle battery isolator.
System Basics:
Goal of BS2 integration:
My understanding of the functional components:
Notes:
Questions:
Thanks much!
System Basics:
- This is being used on a Mobile Command Center (MCC/CIC) vehicle - think an RV with communications and logistical gear.
- There are 2 independent and electrically isolated battery systems (common ground), one for the chassis and another for the command center.
- The chassis system consists of one 12vdc battery and is charged from the alternator at typical vehicle voltages (14.4 Vmax)
- The command center system consists of a 12vdc battery bank and is charged using a 100amp programmable charger, itself powered from either shore power or an associated in vehicle generator.
- The command center batteries require 15.3 Volts for absorption and 15.6 Volts for equalization.
- The max voltage allowed on the chassis system is 14.4 Volts.
- There is currently a 200 amp isolation solenoid which can combine the systems to allow the alternator to charge the command center batteries when the vehicle engine is running.
- Currently, the solenoid is manually closed and opened via an spst.
Goal of BS2 integration:
- Monitor the voltages of both the chassis (V1) and command center (V2)
- Control the Solenoid based on the voltages or a user override.
My understanding of the functional components:
- ADC to acquire voltages
- User input of some kind
- Small LCD display to display status and voltages (also left over from an earlier project)
- Solenoid control circuit - likely via a mosfet.
Notes:
- It has been a long time (ok, a decade) since I worked with microcontrollers.
- my electrical theory/circuitry classes I had in college were before that.
Questions:
- What is the best way, and specific components, to get the voltages into the stamp?
- Do I need optoisolators?
- Is there a good way to make this fail open?
- What would a guess-timated response time be from measurement to opening the relay given reasonably efficient code?
- What else should I be considering / asking?
Thanks much!
Comments
The Stamp should be able to do this for you without too much trouble.
Because you have a common ground, the two batteries can be sensed on separate channels of a dual a/d converter ( ltc1298 is a possibility).
The LCD will be driven off a Stamp pin serially.
The inputs to the Stamp have to be 5 volts max so they will be through voltage dividers or opto-isolators. And, you will have to have a 5 volt supply for the Stamp. I'd suggest a 1 A switching-type just for good performance with your slightly varying input voltage. That switcher could be fed through isolation diodes from both batteries if you wish the redundancy. The Stamp power input could possibly benefit from a couple of small capacitors to keep the high frequency noise out of the system.
Driving the solenoid through a mosfet makes sense (with a kick-back diode on the solenoid coil)
As for speed of response, the solenoid will be the slowest thing in the circuit. I'd picture the Stamp scanning the inputs, updating the LCD, updating the a/d , and controlling the solenoid with a refresh of 0.5 or 0.75 seconds.
I'd suggest coming up with a proposed schematic and bit of description of what the Stamp inputs would be and the desired response to the various operating parameters.
Cheers,
I'll put together a schematic and diagram and add it to the thread.
Any assistance with keeping noise down (bypass cap sizing, trace routes for later PCB creation, and grounding, etc.) is very welcome.
Any thoughts on the HAAS 200-s Current sensor would also be greatly appreciated -- especially as configured in schematic.
Digikey page here:
http://www.digikey.com/product-search/en?KeyWords=398-1064-ND&WT.z_header=search_go
Data sheet is here:
http://www.lem.com/docs/products/hass_e_rev14.pdf
Circuit uses 1A at 5vdc switching power supply
Data sheet is here:
http://www.recom-power.com/pdf/Innoline/R-78xx-1.0.pdf
And, the schematic:
Vehicle Battery Isolator Relay Control - v2.pdf
Other thoughts and suggestions are also much appreciated.
As well, your choice of 5v supply seems more than adequate. Check for any recommended large capacitor on the output.
The Stamp might also benefit from a small cap ( 0.01 uF) in parallel with the 1.0 uF.
Keep the leads from the reset switch very short and away from any leads that may switch large currents. FWIW, I seldom use a reset because it usually causes more problems than it solves.
Keep us informed of your progress.
Cheers,
'
I don't know enough from your posts about the battery's. The voltages is confusing. You can mess up Lithium battery's with the wrong voltage.
'
Most member's don't have time to look though multiple links. But will review one or two at a time.
Hi Walt, thanks for the note and I appreciate your comment regarding LiFePo4 batteries. You hit on the heart of the project.
The circuit is specifically designed to
A. independently monitor the voltages of 1. the chassis and 2. the command center.
B. monitor the instantaneous current transfer between the Chassis and Command Center.
C. Only close (or maintain as closed) the isolation relay when the readings are compatible across both the Chassis and Command Center.
Note: In addition to being aware of incompatible battery voltages, the chassis electronics (ecu, obd modules, etc.) would likely be damaged by the (absorption & equalization) charging voltages of the Command Center - the circuit protects from this as well.
I have created a new thread for this project in the "Projects Forum" -- with a bit more concise information.
http://forums.parallax.com/showthread.php/159838-BS2-as-vehicle-battery-isolator-controller-help-request-%28with-schematic%29
Again, thank you for your thoughts and time.