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electrical:12v:multipoint_charging [2022/05/25 16:26]
frater_secessus [why one source wins] |
electrical:12v:multipoint_charging [2025/08/02 15:17] (current)
frater_secessus [how to make them cooperate] I=V/R |
| So how do we make them all charge all the time?((and this even a thing you want?)) | So how do we make them all charge all the time?((and this even a thing you want?)) |
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| Barring heroic measures((exotic alternators/regulators, [[electrical:12v:b2b|DC-DC chargers]])) the alternator is going to stop contributing at some point during Bulk charging. That is ok, the alternator provided a ton of current while it was charging. | Without outside help from [[electrical:12v:b2b|DC-DC chargers]] or exotic alternators/regulators, alternator contribution is going to taper and eventually stop. Direct charging with a relay uses the difference in voltage between the higher chassis voltage and lower bank voltage to get current into the bank. As bank voltage rises this voltage difference ("delta") decreases therefore so does current.((At some point solar-charged bank voltage may be higher than the chassis voltage, at which point the solar is helping run the chassis electronics. This may slow bank charging so you could [[electrical:12v:alternator#disabling_alternator_charging|disable alternator charging]] at that point.)) This relationship is described in the formula [[electrical:12v:directcharginglfp#the_formula_in_60_seconds|I=V/R]]. |
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| But if you want to the charge controllers (and some [[electrical:converter|converters]]) can be convinced to stay //roughly// in sync and keep charging together. This is done by **configuring the Absorption and Float setpoints on the controllers to be the same**.((including Absorption termination setpoints like time or current)) There will be short periods where one controller makes a change before the other, but for most of the time both will be contributing at the same time. | But if you want to the charge controllers (and some [[electrical:converter|converters]]) can be convinced to stay //roughly// in sync and keep charging together. This is done by **configuring the Absorption and Float setpoints on the controllers to be the same**.((including Absorption termination setpoints like time or current)) There will be short periods where one controller makes a change before the other, but for most of the time both will be contributing at the same time. Even if they contribute unequally it is a non-issue because the voltage setpoint is being held. If a big load is added or conditions deteriorate it will be "all hands on deck" as in the Bulk stage scenario above. |
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| Note: there are high-end controllers/chargers which communicate with each other to coordinate charging. That feature is beyond the scope of this article. | Note: there are high-end controllers/chargers which communicate with each other to coordinate charging. That feature is beyond the scope of this article. |
| Some of these are observed, and some are theoretical. | Some of these are observed, and some are theoretical. |
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| * the vagaries of voltage sag across the system may result in the various charging sources seeing slightly different voltages. Voltage Sense wires can help with this issue. | * the vagaries of voltage sag across the system may result in the various charging sources seeing slightly different voltages and therefore contributing in unpredictable ways.((probably a non-issue as long as the bank is getting properly charged)) Voltage Sense wires can help with this issue. |
| * Multiple controllers set up to trigger Float from endAmps((trailing amps)) may enter float early since they are providing only some of the charging current. | * Multiple non-communicating controllers set up to trigger Float from endAmps((trailing amps)) may enter float early since they are providing only some of the charging current. |
| * Multiple sources may inadvertently exceed the bank's recommended charging current | * Multiple sources may inadvertently exceed the bank's recommended charging current, or your preferred current. Example: a lithium battery wants 50A max but each charging source can make 30A. This might result in overcurrent (60A) during Bulk. |
| * theoretical: low-frequency PWM controllers in parallel with MPPT controllers may confuse the MPPT with a varying Vbatt reference. | * theoretical: low-frequency PWM controllers in parallel with MPPT controllers may confuse the latter with an unstable reference voltage. |
| | * some systems may throw a warning if chassis voltage > alternator output voltage((https://www.cruisersforum.com/forums/f14/alternator-solar-panel-conflict-233083.html)) |
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