Using two chargers ?

Tikvah · May 03, 2017, 03:14:57 PM

I think I already know the answer, but I want to double check before I smoke something.

24V House Bank (8 Golf cart batteries) On Pole power
I have an inverter that charges my batteries, but occasionally I want faster charge. So I have a second, 50A/24V charger. Can the charger and the inverter/charger both charge the batteries at the same time? I plan to attach the + /- charging cables to the same location and turn them both on.

Any problem with backfeed?

bobofthenorth · May 03, 2017, 04:45:28 PM

Its unlikely that they will play nice with each other but I can't see a scenario that lets the smoke out either. Only one of them will end up doing most of the charging. Even so-called smart chargers can't defy Ohms law. Most likely your fast charger will only look at voltage so it will be the first to drop out. On the boat I had three charge systems - dual alternators on the engines, solar & a Freedom 25. I did precisely nothing to help them co-exist and they worked just fine.

Tikvah · May 03, 2017, 04:48:05 PM

It crosses my mind that there are occasions that the engine is running while still on pole power (or generator) and both the alternator and inverter/charger are potentially sending power to the batteries.

Utahclaimjumper · May 04, 2017, 02:07:50 AM

They are also seperatly regulated,, so no harm no foul.>>>Dan

bevans6 · May 04, 2017, 06:02:36 AM

As noted, depending on how smart the chargers are at sensing battery state of charge, one or both will essentially turn off and go to trickle charge or off regardless of the batteries actual state of charge. I did that once, by oversight, and basically nothing happened, nothing good or bad. The chargers both decided the batteries were at 100% and quit.

Oonrahnjay · May 04, 2017, 06:23:57 AM

Quote from: bevans6 on May 04, 2017, 06:02:36 AM... The chargers both decided the batteries were at 100% and quit.

Brian, if the batteries weren't fully charged, isn't that kinda bad? Undercharging is bad for batteries and can/will contribute to reduced battery life. It sort of seems to me that one good charger - of the correct charging capacity - is the best way to go to get good, uncomplicated full charging as quickly as possible. I don't know of any real problem caused, but it seems to me that there's a pretty good chance of two chargers "crosstalking" and making each other "think" that incorrect states are correct.

Uncle Augie · May 04, 2017, 07:54:54 AM

Quote from: Oonrahnjay on May 04, 2017, 06:23:57 AM
Brian, if the batteries weren't fully charged, isn't that kinda bad? Undercharging is bad for batteries and can/will contribute to reduced battery life.

Lead Acid like to be as clost to 100% as much of the time as possible. Lipo are ok never getting to 100% always floating around 60-80%

bobofthenorth · May 04, 2017, 02:20:35 PM

Quote from: bevans6 on May 04, 2017, 06:02:36 AM
As noted, depending on how smart the chargers are at sensing battery state of charge, one or both will essentially turn off and go to trickle charge or off regardless of the batteries actual state of charge. I did that once, by oversight, and basically nothing happened, nothing good or bad. The chargers both decided the batteries were at 100% and quit.

I'm sorry Brian but that makes no sense. The chargers see the voltage across the batteries. All chargers that I am familiar with make some use of voltage in their charge algorithm. The more complex chargers look for voltage and current but they all start with voltage. Until the batteries are charged both those chargers had to see less than "charged" (pick a number) voltage so at least one of them should have kept on charging at least until the battery voltage exceeded what each charger considered a charged voltage.

I can imagine a situation where a pair of 3 stage chargers could fool each other into going into float early in the cycle before the battery had any significant charge but they would still continue to charge, just at a much reduced rate.

Lee Bradley · May 04, 2017, 02:56:23 PM

If the charges see voltage across the batteries and another charger is hooked across the battery, wouldn't the charger see the other charger voltage instead of the battery voltage?

Utahclaimjumper · May 04, 2017, 07:56:11 PM

NO the battery/s will average and smooth the charge level.>>>Dan (same as a capacitor)

buswarrior · May 05, 2017, 05:36:55 AM

Tikvah, do you have a decent SOC meter/system?

An experiment is in order?

See if connecting them both changes any of the readings, or the outcome?

the consensus is that the two will just argue with each other, and that ultimately, something will go into the batteries, without damaging anything.

So, field test time?

happy coaching!
buswarrior

bevans6 · May 05, 2017, 05:40:39 AM

Quote from: bobofthenorth on May 04, 2017, 02:20:35 PM
I'm sorry Brian but that makes no sense. The chargers see the voltage across the batteries. All chargers that I am familiar with make some use of voltage in their charge algorithm. The more complex chargers look for voltage and current but they all start with voltage. Until the batteries are charged both those chargers had to see less than "charged" (pick a number) voltage so at least one of them should have kept on charging at least until the battery voltage exceeded what each charger considered a charged voltage.

I can imagine a situation where a pair of 3 stage chargers could fool each other into going into float early in the cycle before the battery had any significant charge but they would still continue to charge, just at a much reduced rate.

"I can imagine a situation where a pair of 3 stage chargers could fool each other into going into float early in the cycle before the battery had any significant charge but they would still continue to charge, just at a much reduced rate." which is exactly what happened. One was a small, cheap three stage Schumacher that is prone to going to float charge ( basically no amps and 13.6 volts) somewhat prematurely, and one was another smart charger of uncertain brand. Basically they both went to float charge. I just unhooked one and reset the other, probably. I have a lot of different chargers. That little 6A Schumacher is great for float maintenence, but lousy for charging. I have another 30 amp smart charger that is great for charging but doesn't have a maintenance mode, so it lets the batteries discharge after it turns off. Now, of course, I use the Magnum for the bus, but the truck and the tractor are a pita.

Lee Bradley · May 05, 2017, 12:38:34 PM

Quote from: Utahclaimjumper on May 04, 2017, 07:56:11 PM
NO the battery/s will average and smooth the charge level.>>>Dan (same as a capacitor)

But the battery doesn't determine charging voltage that is done by the charger. The system voltage must be greater than the battery voltage or no charging takes place.

Iceni John · May 05, 2017, 03:37:54 PM

On the NAWS solar forum the general consensus of opinion from the gurus there is that you can have more than one solar charge controller connected to a battery bank, and each CC will charge according to its designated charging parameters. Wouldn't normal battery chargers follow these same principles?

There's a "smart" charger that goes under the name of Mean Well (would you trust anything called that?) that resolutely refuses to function at all if there's anything else connected to the battery! Just like with some people, "smart" doesn't always equate to "practical in the real world".

John