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Backup for charging PV battery pack

 
pollinator
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https://www.ebay.com/itm/254451756993?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&mkcid=2&itemid=254451756993&targetid=1263094004826&device=c&mktype=pla&googleloc=21161&poi=&campaignid=10454522294&mkgroupid=121089751606&rlsatarget=pla-1263094004826&abcId=2146002&merchantid=6296724&gclid=CjwKCAjw87SHBhBiEiwAukSeUUd-4Q6F2BycyI05JmUjjHd1mNlQEYpvhmOm9Z7EInu1p-vEXtahBRoCNt4QAvD_BwE


Not endorsing this product, but throwing it out here for discussion.  I read of a lot of folks going to 48v battery packs for the PV systems.  This kind of alternator ( probably not one but in multiples to get enough power) looks like it would be a good candidate connected to a small diesel engine to recharge the battery pack when days are cloudy, or some part of the system is not functioning  properly.  Am I am on the right track?  Does a 48v alternator actually product more than 48v?  My ebike battery charger is 48v, but it charges up to 53 or 54 volts.
 
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Yes it will be above 48v.  Charging is only done when the voltage is higher at the alternator than the battery.  The voltage pushes it there.  It is like water that is in two buckets that are connected at the bottom with a pipe.  If you fill one the other will fill until they are equal.

The voltage for battery charging depends on the type of batteries. Lead acid is usually between 54 and 56 volts set by a regulator.

I just finished a project using 2 x 48v x 200amp alternators.  I used a mechanical regulator to control both fields/alternators at the same time.  The 48v nominal solar power is quite common here.   Inverters react much quicker with the higher voltage and the line sizes are smaller.  Brushless permanent magnet are my favorote.

 
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I guess if you had the motor laying around and had something to mount it to and could rig up a fuel tank and everything associated with it then that would be an option.  But otherwise you would be miles ahead just buying a generator.  You can get a 2000W generator for only a few bucks more.
 
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Charging battery packs from a solar panel isn't as straightforward as you think – even if the solar panel output is regulated. We recently tested 10 different battery packs and 6 had serious problems with solar charging, while 2 more had minor problems
 
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