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Nzgrant

Battery charger an solar

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Do I need to disconnect the solar panel if I need to run the battery charger? And yes yes I know with solar I wont need to run the charger but I did have to.

 

Also a mate was told to disconnect his solar panel when he starts the engine. Any idea why that would be? We certainly dont. Am I doing it wrong?

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No on both counts. No need to disconnect panels or charge regulators for any normal reason.
There should be back current/surge protection built into the reg unless it is a realy nasty cheap piece of crap.
And when ever other charge source/s are connected, the one that puts out the greater regulated voltage ends up causing the other regs to back off and the greater charge voltage becomes sole charge source. This is a real pain in the A when you want the greater charge current to be the primary charge source. Someone needs to design a single charge reg that combines all source currents and feeds that as a single regulated output.

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I turn off my panels when running engine so the alternator is the sole provider of charging current.  I assumed the charge voltage of the solar charging would limit the current from the alternator as the reg would see the high voltage?

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If the voltage is high, the batts will only accept a small charge. No need to turn any regulated charge source off. As wheels said, the reg with the highest voltage setting will win. Otherwise, if the batts volts is low, all sources will charge until they reach their cut off voltage.

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This is a real pain in the A when you want the greater charge current to be the primary charge source. Someone needs to design a single charge reg that combines all source currents and feeds that as a single regulated output.

Apparently the guys at Wakespeed are working on a device such as this right now, how long until it gets to market could be another thing entirely. Their WS500 alternator reg is very good though.

http://www.wakespeed.com/

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 This is a real pain in the A when you want the greater charge current to be the primary charge source. Someone needs to design a single charge reg that combines all source currents and feeds that as a single regulated output.

 

The batteries resistance dictates charge acceptance and ohms law would cause a higher current if available to be the primary source.     

 

You could easily combine multiple different output voltages into a single static output voltage using  buck boost regulators and feed the single regulated voltage to a single Mttp controller that could handle the combined amperage.   I would exclude a wind generator from this though. 

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The batteries resistance dictates charge acceptance and ohms law would cause a higher current if available to be the primary source.

 

You don't understand how these regs work. First of all, you cannot use ohms law to calculate the charge current into the battery. Your comment would be correct if it were simple single stage current regulation. But multistep charge regulators don't work that way. They are changing modes from Voltage regulation to Current regulation and then Voltage regulation again. They sense the voltage level, placing then into their different modes or steps of regulation depending on the Voltage sensed and depending on the trigger points of the steps. Of which, some regs can have those trigger points manually set. For instance, the bulk charge voltage can usually range from 14.1V (nominal is 14,4V) to 14.8V. The float charge can range from 13.3V to 13.8V. So while bulk charging, all regs are poking in current. As soon as a reg senses the trigger voltage, it's output drops to float level and no longer charges due to the other reg/s continuing to supply the greater bulk charge. If you have a sophisticated reg that does a 3 step regulation producing an absorption charge, then that reg no longer pushes current into the battery. It is like a tandem bike and one regulator is not trying hard peddling letting the other do all the work.

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While that is true Wheels, normally they all work while in Bulk, which usually gets the batts to about 80%. Its not called bulk for no reason, it's where most of the charging happens. After that, then any sources will drop off one by one, the one with the highest voltage settings last. Once lead acid batts are over 80%, the charge accepted drops away pretty quickly, and the fuller the charge, the lower the charge rate, so as you approach full you don't need a huge charger, as the batts wont accept it anyway.

Of course, none of that means you should not think about this, and set up your sources to get the best possible benefit - which, by the way, is not just fast charging, but maintenance resulting in healthy, long lived batts.

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 First of all, you cannot use ohms law to calculate the charge current into the battery.

 

Easy.   Batteries resistance [at its current state of charge - this changes as it charges] / voltage = Current.    I = R/V is ohms law and this is a prefect example of how it works.   A battery changer can not rewrite the laws of physics.

 

I am very aware of how these chargers work but they are mostly a triumph of marketing over technology. 

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.... What about the battery EMF which is increasing as the battery charges? You can't say that the resistance is the charging voltage/charging current. The battery internal resistance will be (charging voltage - battery EMF)/charging current.

I'll be generous and suggest I=R/V is a typo on your part.

Edited by Luigi Vercotti

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