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As for the actual brand name and battery model... Quote:
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Otis - It sounds like you have a well thought out electrical design.
Primarily as a personal query, do you have discrete panel indicators for your batteries and alternator? I have a smart indicator on each battery as well as my EMS showing bus voltage. I currently do not have an automatic “crowbar” component. |
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I had one over voltage incident over the years, and that is when I found out crowbar over voltage protection is great in theory but this time it did not work. It took a few minutes to recognize what was going on, then I tripped the alternator. Voltage got to about 16vdc, not enough to fry anything. My point, as the alternator output voltage increased the standard dumb battery I was using transformed the excess output current into heat. This provided a few minutes of time to figure out what was going on as the battery load kept the buss voltage from spiking. Based on all this discussion, I assume (correct me if I'm wrong) that when a BMS systems protects the battery from over voltage the battery is removed as a load on the alternator. So applying to my incident the buss voltage would have continued to rise. I wonder how many people flying with such batteries actually test whatever over voltage protection they are using. Considering the critical aspect, perhaps a primary and backup over voltage protection schemes would be appropriate. Carl |
Sounds like...
we need to keep in mind how voltage (pressure) works.
If an alternator/regulator in runaway is applying 17 volts of electromotive force across a pair of terminals that are in common with a battery, and said battery has a BMS that will not allow an inward (charging) current at that voltage level, the battery is effectively removed as a load and its float voltage of 13 or 14 volts is irrelevant to what the circuit will see. The impressed voltage from the alternator is all that matters in that case. The alternator/regulator will have to behave as if the battery is not present until the BMS decides to let the battery act as a load again (accept an inflow charging current). The fact that this taking-itself-offline behavior is temporary and automatically reversible for the EarthX BMS is a crucial point, and seems to be the crux of what Glen experienced when his non-EarthX battery surprised him and went offline for an unquantified period of time even after the bus voltage dropped below overvolt levels. Just my armchair quarterbacking, here. But I wanted to jump in and clarify that 13V and 17V cannot exist on the same wire at the same time. Voltage is pressure - not flow, not widgets. This thread has been very helpful in stimulating research and forethought, and in boosting confidence in the EarthX BMS in my planned application (2 B and C alternators and regulators with crowbar OVP). |
From my reading of different BMS?s behaviors, a key feature of the EarthX BMS appears to be its ability to differentiate a high operating temperature while under extreme load vs under a more normal load. This differentiation means it can shutdown under the condition of high internal temperature from excessive starter time but not shut down from high temperature environmental conditions.
While high environmental conditions are not good for the battery, the BMS has been designed to continue providing electricity. This is important for aircraft but less important for typical ground vehicles. Assuming my situation was caused by high heat (still not yet determined) I can assume the BMS in my battery does not differentiate the reason for heat and lumps it all under the category of ?battery self preservation? and takes preventative action to protect itself. |
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I’ve not mentioned the vendor as the situation is still under investigation and it would be inappropriate to suggest anything disparaging without all of the facts. My RV-8 has the battery on the firewall. |
your crowbar?
With all this analyzing OP wants us to start doing... this seems like a good time to ask why we don't all have overvoltage tripping devices installed in our airplanes?
B&C and PlanePower alternators have crowbars as standard, and you can buy a standalone crowbar from Bob Nuckolls (plus info on how to implement it), so to me there's really no excuse not to have one, especially if you choose to have a LiFePO battery on board. Which got me thinking how to test the crowbar in the airplane as part of a maintenance routine: you could connect a variable DC power supply to the B-post of the alternator, turn on the Master switch on the panel (if you don't have an Avionics Master, then pull the breakers/fuses to your expensive electronics), and then increase the voltage until the Field breaker pops. If it doesn't trip by, say, 16V, then you know you have a problem. |
Here is a LINK to a thread describing one way to test an over-voltage module.
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http://www.vansairforce.com/communit...Dual+batteries It is absolutely symmetrical, so it matters not at all which battery you choose to act as primary on a given flight, and there are no emergency procedures. The essential loads switches and voltmeters are located in a vertical sub-panel console below the throttle(RV-7A), and the relative voltage readings tell you which is on the main bus and which is on diodes. If your altetnator has a built-in regulator, replacing it with a B&C and crowbar protected regulator will be a very worthwhile investment.- Otis |
Postmortem: alternator internal voltage regulator failure
tl;dr
To answer which problem came first, the alternator or the battery? The alternator. details: I performed a bench test of the alternator (standard Vans model with internal voltage regulator installed 590 hours ago). At the engine equivalent of 1000RPM, the alternator output voltage was 16.1V with a 2Amp load. With an old PC680 battery - with an initial no load voltage of 12.3V - added to the test circuit, the circuit voltage was 14.7 and starting to climb back up. My conclusion is the Antigravity ATX20-RS BMS internal regulator - which is designed to handle short spikes - had worked much longer than it was designed and the battery internal temperature rose to the point the BMS eventually disengaged. Up until that point, the battery was taking enough load to keep my EMS voltage sensor below the 15V warning setting. Once the battery disconnected, the remaining circuits were not a significant load, and the voltage started to rise. |
finding a ''crowbar'' that disconnects the alternator b lead from the system is not as easy as calling some vendors ,even though they advertise a product. they will discourage its use for this purpose.
perihelion [?] does have equipment made for exactly this application. i put one of their ovm's in that disconnects a 200 amp relay between the alternator and the main bus. also, anyone thinking about checking their ovm should be aware that you may fry an alternator by disconnecting it from a heavy load. |
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