A communication with an electrician made me somewhat unsure about my installation. I am 70% through installing a new system on a sailing boat, as schematically illustrated in the attached document. My question concerns the Orion XS: can that be installed after the FET?
I like the Orion to be at the FET because a shore powered charger on the starter battery will then never activate the Orion. With the alternator running, the other (non-lithium) batteries will act as a voltage buffer, so that the Orion XS can be activated based on a sufficiently high voltage. Most of the time, i.e. when the alternator is not running, however, the Orion will not have an input.
This is not a great idea, since by definition the ArgoFET outputs are separated from each other, which means that the Orion XS will not have the required Pb battery on its input as a âbufferâ.
It would likely work in this configuration for a while, but the Orion XS is likely to suffer non-warrantable failure in this proposed non-supported installation.
hmmmm, I would like to argue that the battery serves as a buffer to the Orion despite both being separated by a FET (provided the difference between âshutdown voltageâ and âstart voltageâ is not chosen too large).
Here is my rational: when the alternator is running, there is a voltage at the battery of about 1.0 to 1.5 V above the current the battery would/will acquire without an alternator. For all voltages within that window of voltage, the FET is âopenâ towards the Pb batteries. That gives a window of, say, 0.7 V (between âstart voltageâ and âshutdown voltageâ) for the Orion XS to safely operate. The Orion XS, once it starts to draw current (during charging), will lead to a drop in voltage on all FET outputs. If the voltage drop, however, is kept within the window of (say) 0.7V, there will always be a counter voltage on the conventional Pb batteries (i.e. the FET is open towards the Ph batteries). This is what I referred to as âbufferâ, because the current/voltage control of the Orion can operate with sound current stability due to the other Pb batteries. Do I make a mistake in this thought (you are an Expert and I value your response)?
By definition the ArgoFET Battery Isolator prevents the Orion from being connected to the Pb batteries, so by connecting the Orion to one of its outputs youâre isolating the Orion from the Pb batteries. Something that itâs isolated from canât be a buffer for it. I understand the rationale that the batteries present on the first two outputs will help stabilize the input voltage, but thatâs a theoretical approach that depends on the operation of those two batteries, whether theyâre fully charged or not, whether their main fuses are intact, and doesnât assist in the event of voltage spike caused by sudden output cessation from an instance like the BMS shutting off the ATC.
Why not just connect it from one of your start batteries, and use an ignition trigger so that it doesnât turn on unless your ignition is on?
yes, I assume (one of) the two Ph batteries are intact. If they wouldnât my alternator would overheat and blow.
Wiring the ignition trigger is quite some effort on my boat, but earlier, I considered an electronic switch, which turns the Orion XS off, once AC voltage for the shore power charger is on. I would like a set-up without an additional switch, according to the scheme attached in my initial post - but based on your comment I might reconsider this concept. Thanks for your answer.
I havnât tested the setup yet. I am still convinced I have a voltage window of about 1 to 1.5 V (which the alternator provides on top of the Pb batteries voltage). This window should be sufficient to operate the Orion XS. But no, I yet have to realize this connection and thoroughly test it.
Iâve thought about this setup since it is nearly identical to mine (in my case, the AGM charger was turned off). I believe I have narrowed down the issue that causes the voltage spikes. I have not tested this reasoning, but it is the only explanation that makes sense to meâboth for my setup and for yours. Feel free to disagree or point out errors in my reasoning; I would appreciate it. See also: What is wrong with this Agrofet and Orion-Tr Smart installation?
Your setup is likely to cause voltage spikes at the alternator and the batteries. An Agrofet should not be used with an Orion charger when the damping battery is behind an Agrofet output. Hereâs why:
Remember that the Agrofet will close (allow current to flow) when the voltage at the input is slightly higher than the voltage at an output. The sequence that causes spikes is as follows (example in a 24V system):
The alternator is turned on and generates a steady 28V. This is higher than the output voltage at both the battery and the Orion. The Agrofet allows current to flow to both outputs.
The battery voltage rises to 28V as expected.
After a whileâdepending on your Orion configurationâthe Orion starts charging. This causes an immediate drop in voltage that can be measured at the alternator.
The battery is slower to lower its voltage (itâs a battery!), so for a brief moment the output side of the Agrofet (to the battery) has a higher voltage than the input of the Agrofet. The Agrofet opens this circuit and disconnects the battery completely.
Now the damping battery is no longer connected to the running alternator. This causes the voltage to fluctuate. The Orion, if it is cycling on and off, compounds the problem (for example, due to voltage lock).
When the alternator voltage rises above the battery voltage (say it spikes to 30V), the Agrofet allows current to flow to the battery. This raises the battery voltage, stabilizes the alternator at 28V, and then immediately disconnects the battery again (since the battery is now sitting around 30V, higher than the alternatorâs stable voltage).
This cycleâlasting only a few millisecondsârepeats over and over. In my case, I observed brief voltages as high as 40V.