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Drive capability of the LOW output
My question is about the Low output for the low fuel light. You stated in your documentation that the output is "10 to 12 volts". Does the output have enough drive capability to operate an automotive style relay? If I connect it to a relay coil would I also need a snubber diode across the coil?
I am using the AMP for a motorcycle conversion. I have a Curtis 1238 controller driving an HPEVS AC-20 motor and a 32 cell 100AH GBS battery pack. I want to switch one of the inputs to the Curtis (Economy Mode) using a small relay driven from the AMP.
The LOW (and TACH) circuits can both sink and source current. At the moment, the AMP will make that LOW signal (as in Low battery status) go HIGH (to around 10 volts) when the SOC goes below whatever threshold you set up with the software.
The engineer who designed these circuits is working on some documentation showing exactly how this circuit works, how to connect to a relay and what the maximum current draw would be. We will get some updates posted here shortly.
Also, what is the part number of the relay you were thinking of using? We might also give you some suggestions if you want.
Thanks for getting back to me. I haven't picked out a relay yet so if you have a suggestion let me know. Would a solid state relay be a good choice? An opto coupled control circuit would eliminate the need for the diode and cap.
The sketch is helpful in understanding what the circuitry looks like. I look forward to more info. In the sketch you provided the LOW signal would have to act as the sink for the current through the relay coil. Would that mean the input is active (relay ON) until the battery gets low? I guess I need to see how the source driver is configured.
I am switching a 12V logic input to the Curtis controller and want to drive an LED indicator on the instrument panel at the same time. I need a normally open output until the battery gets low. A SPDT relay could invert this by using the NC contact. The 12V logic voltage to be switched has to be isolated from the 12 volt DC/DC converter (the Curtis provide its own logic voltage), thus the need for a relay.
The LOW circuit will be used to put the controller in Economy mode which has its own current limit settings. The idea is to set the current limit to a low number as a sort of limp home mode. This isn't holding me up, I just thought is would be a neat feature to try out. If worse comes to worse, I can just turn on a light and have the human flip a switch.
I'm almost done with the 12V wiring and should be ready for a test drive soon. Family coming into town for Easter, so I don't know if it will be this weekend or not.
The LOW signal is active-high. When the State Of Charge goes below the set threshold, the LOW output will drive high (~12V).
LOW condition met: Output is at 12V, can source current.
Low condition not met: Output is at GND, can sink current.
The purpose of my (messy) sketch was to show how to drive a relay using the LOW drive circuit as a current sink, which may suit your application or not. The impedance of the drive circuit is less when using it as a current sink. However, there is no reason why you can't use the LOW output as a current source. Any general purpose relay, such as Digikey part# PB1321-ND, will work just fine with the LOW output. Long story short, the LOW output can drive a small to medium sized relay without any problems.
Also, the LOW output should be able to drive an opto just fine. Feel free to send any datasheets for components you are considering interfacing to the LOW output and I can make further recommendations.
LOW output as a current source: LOW --> load(coil) --> GND (same GND as the ABAmp)
Summary: This will be a 12V drive into the load.
LOW output as a current sink: V+ --> load(coil) --> LOW
Note: GND of V+ must be the same as ABAmp GND.
Summary: This configuration can sink current from voltage sources less than 12V.
I hope this helps.
Thanks. On the motorcycle project I have used the standard automotive type relays for everything else. They typically have a coil resistance of about 85 ohms. The Digikey relay you suggested lists a 200 ohm coil resistance. Is 85 ohms too much of a load? I will probably make a small board with some 6 pin dip opto relays that can switch 2 amps out current with only a 10 mA control current. A 30 amp automotive style relay is overkill for switching an LED indicator and a logic input.
This weekend I hope to get the instrument panel and indicators connected to try all this out.
Again, thanks for the help.
85 Ohms should be fine, and it still leaves some headroom.
I got to do the initial ride around the block on Sunday (4-27-14). The bike runs great and the AMP works as advertised. I was curious to see whether the tach ammeter would see the regen current and it does indeed. Great fun!
I have a question about the ZERO line and the fuel gauge reset. After driving around for twenty five miles or so the fuel gauge was showing a little less than 2/3 full. That seems about right. I connected the charger and let it charge for about a half hour before I disconnected the charger and turned the 12V off the first time. It looked like the fuel gauge had moved slightly back towards 3/4 before I shut everything off. The next time I turned the 12V back on the fuel gauge showed full. The charger only had enough time to add about 6 amp hours (100AH pack) so I would not have expected it to go all the way back to full.
I have not connected the ZERO line to anything yet, it is floating. Should I use a pull up resistior? Do I need to leave the 12V to the AMP turned on to retain the fuel gauge reading? If I have to leave 12V connected all the time what is the current draw?
I will be testing more this weekend, I'll let you know if I figure anything out.
Sorry for the late reply... my last post got lost, or isn't up here anymore.
I checked and the ABAmp currently does not store the State of Charge to survive a power cycle. Sorry.
However, the ABAmp only draws 30mA (with no external loads active). You may be able to leave it connected to your system indefinitely.
What is the size/capacity of your battery array?
My battery pack is a 100AH X 32 cell system, about 10KWH. My 12V system runs on a DC-DC converter which powers up all the 12V loads. I have a small (1.2AH) 12V bootstrap battery to operate the relay that turns on the DC-DC converter. 30 mA from the main pack would not be an issue, but with the little 1.2 AH starting battery it would only last for a day or two.
I will turn off all the 12V loads except the AMP to see what I can get the current draw down to with the DC-DC converter powered up. Right now with all the 12V loads on except the lights, I draw about 0.9 amp off the main pack. I might have to rearrange some connections to minimize the loads with the key off.
Is it possible with the current hardware design to include a standby function? I have a GPS speedometer installed that has a standby line to retain the position information. They must be keeping a memory function alive because it only draws 25 micro amps. I have that tied to my little starting battery. Future upgrade perhaps?
Our design requires that the State of Charge be stored in a non-volatile RAM. Actually, this is one of the features that is at the top of the list. I'll try to get you an ETA on when that function will be released.
Any update on the NV storage of the fuel gauge level? The AMP is working great otherwise.
Fuel Gauge Update
To save the fuel gauge reading between recharges, I added a second DC/DC converter to keep the AMP powered at all times. I found a small (24 Watt) unit that only draws about 15 mA from the main pack when connected to the AMP. So far so good.
While I was installing the new power supply last night I finally got around to installing a push button switch on the ZERO line. Per the documentation I carefully hooked one side of the switch to the ZERO line and the other to ground. Then I went for a test drive to use up some of the charge since at the time I had just finished recharging. The plan was to push the button to see the fuel gauge reset, charge back to full, then reset once more.
When I drove off, I noticed the amp reading was staying on zero. Strange, that has worked perfectly since day one. Returned to the shop to investigate. I finally determined that the push button I had installed was a normally closed type that opened when I pushed the button. Not sure where it came from, it was in my electronics box. Of cooourse I did not put the meter on it before hand to verify what type of switch it was. Go figure. FYI, when I noticed the amp meter not responding I naturally hit the throttle with what would typically be a 300 amp or so blast (with the Zero line grounded). However, once I disconnected the switch it was apparent that things were not as they were before.
I was finally able to connect the laptop and get the fuel gauge and tach/ammeter working again, but I had to go through the fuel gauge settings, re zero and cycle power a few times to get it to work. At one point when I powered up the AMP, the tach would go to 550 amps and stay there with no current flowing through the sensor. I (momentarily) grounded the Zero line and the reading went back to normal.
Here is the interesting part: the fuel gauge settings are close but not exactly the same as before.
Recall this is a Speed Hut fuel gauge and 6000 RPM tach. Previously I had Full at 986 and Empty at 476. Now its Full at 920 and empty at 460. I did I hurt something or was I just a little off before? I haven't been paying too much attention to the fuel gauge because it would reset every time I turned off the key.
Also, I noticed a difference in the gauge readings (in test mode) when I disconnected the external 12V power source and ran only on the USB power vs. having both connected. With only USB power, the settings were 380 empty and 760 full. Is this normal?
Aside from my own screw up with the N/C switch, the unit seems to be working well. I have almost a thousand miles on the bike now and it runs and drives great.
Let me know what the plan is with the non volatile storage feature.
I just got an autoblockamp and want to use a raspberry PI for display/control in my EV. Do you have a version that works on the pi? I've tried processing 3.0 on the PI, and basically have given up. It can't seem to find the setControlFont, for the SOClevellabel. I've tried running the processing engine on a Mac and on a PI and get different errors on all of them. I probably have the libraries set up incorrectly, but before I spend more time I figured I'd ask.
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