PD or Iota for my upgrade?
I'm thinking about a converter and battery upgrade. The batteries will be wet cell lead acid 6 volt Possible T-105s or the 230AH, EGC2 from Sam's club. I'll probably go for four. (Does nayone have...
Forum Discussion
I know I've made some lengthy posts, but I want to post an olive branch kind of post. I love facts, and hate disputes. If you read my posts, you might conclude that the dynamic impedance of a battery, as calculated in other posts, isn't relevant to anything in the RV battery system. Nothing could be further from the truth. It's incredibly important to designing the charging system, particularly when it comes to selecting battery charging cables for a charger that does not have a remote sensor on the battery voltage.
The dynamic model resistance (which I've also called AC or dynamic impedance/resistance) plus the cabling resistance sets the charging current flow when you subtract the "ideal" voltage of the battery.
If the resistance of the cables is comparable to the dynamic model resistance, the charging current will be halved. You want the voltage drop across the cables to be significantly less than the dynamic model resistance for maximum charge rate. Of course, you have to know the dynamic resistance (or at least the expected lowest dynamic resistance under high charge rate conditions) to achieve that design goal so you can select the proper low resistance cables.
To put it differently, you want the dynamic model resistance of the battery to dominate the charging behavior of your system, not the cabling resistance if you want short charging times and maximum current output from the charger.
Explaining why large diameter/short cables are important is impossible without an explanation of the dynamic resistance in the battery model. In that scenario, the dynamic model resistance is important and the steady state DC resistance I calculated is irrelevant. OTOH, in testing maximum current capabilities of a charger, it's the other way around. The DC steady state model resistance is relevant and the dynamic model irrelevant.
And to put that differently - the steady state DC resistance model will tell you what the charger can do - the best performance it is capable of achieving. The AC model resistance, in combination with the cabling resistance will tell you what the charger will actually do in your system when charging your batteries having that model resistance through your charging cables.
:)
The dynamic model resistance (which I've also called AC or dynamic impedance/resistance) plus the cabling resistance sets the charging current flow when you subtract the "ideal" voltage of the battery.
If the resistance of the cables is comparable to the dynamic model resistance, the charging current will be halved. You want the voltage drop across the cables to be significantly less than the dynamic model resistance for maximum charge rate. Of course, you have to know the dynamic resistance (or at least the expected lowest dynamic resistance under high charge rate conditions) to achieve that design goal so you can select the proper low resistance cables.
To put it differently, you want the dynamic model resistance of the battery to dominate the charging behavior of your system, not the cabling resistance if you want short charging times and maximum current output from the charger.
Explaining why large diameter/short cables are important is impossible without an explanation of the dynamic resistance in the battery model. In that scenario, the dynamic model resistance is important and the steady state DC resistance I calculated is irrelevant. OTOH, in testing maximum current capabilities of a charger, it's the other way around. The DC steady state model resistance is relevant and the dynamic model irrelevant.
And to put that differently - the steady state DC resistance model will tell you what the charger can do - the best performance it is capable of achieving. The AC model resistance, in combination with the cabling resistance will tell you what the charger will actually do in your system when charging your batteries having that model resistance through your charging cables.
:)
