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Maintaining of a 24 v battery set.


PaulF007
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Would it be possible to use 2 x 12v battery chargers ( Cheap ones) to maintain a back up generator's batteries?

The generator gets used maybe once every two moths but has now failed for the second time because of the batteries . I dont want to fork out R 1500 for a 24v charger so I'm thinking using two small trickle changers to maintain the batteries or will it go poof :) ( AKA @The Terrible Triplett  )

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Interestingly, the Multigrid has the option for a 2nd battery connection to keep it topped up.

Not sure about the Easy Solar.

Do what @Jaco de Jongh did.

Take a 75/15 controller, make the 48v bank the "solar panel".
Connect the 24v batteries to the battery connectors of the 75/15.

 

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I am sure no expert, but that just sounds like a horrible idea :P

Even if it worked, should one of your chargers fail (High likely hood seeing as you have 2) what would happen then?

Pony up and get yourself a nice 24V Charger and you get to sleep safe at night knowing you aren't ruining a nice 24V starter battery :)

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1 hour ago, PaulF007 said:

Would it be possible to use 2 x 12v battery chargers ( Cheap ones) to maintain a back up generator's batteries?

It should work just fine. As long as neither of them does something stupid like earth the negative side. The load side is open circuit, so there is really no way for the current to go than through the one battery it is connected to.

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13 minutes ago, PJJ said:

... sounds like a horrible idea ...

O it works very well. The 75/15 has a lot of configuration. 

How it gets the power does not matter, as long as it is within the controller specs, and 48v bank will never see 75v.

It will keep the batts nice on float, and equalize every 30 day, if it is set to do that. 

So more configuration and cheaper at +-R1100 than a 24v charger.

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1 minute ago, The Terrible Triplett said:

O it works very well. The 75/15 has a lot of configuration. 

How it gets the power does not matter, as long as it is within the controller specs, and 48v bank will never see 75v.

It will keep the batts nice on float, and equalize every 30 day, if it is set to do that. 

So more configuration and cheaper at +-R1100 than a 24v charger.

Oops, I see I  didn't qoute the OP, I was talking about the chargers 2 12V chargers in series.

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2 minutes ago, PaulF007 said:

Cool idea but I would like to use AC , 

Why? Controller uses milliamps if the batts are full?

Any case, the ideas are now flowing! :-) 

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Wait... Do a cost analysis...

The only way I can see this working (properly) with 2 seperate chargers connected in series to a 24V setup (like your generator) is that you will need to have some kind of monitoring device and a battery balancer? Cost of a battery balancer + cost of a monitoring device like a BMV702 (you want to watch the midpoint in case a single cell fails in one of the batteries), just seems to hugely outweigh the cost of a 24V charger/monitor...

There are right ways & cheapie ways - if staying cheapie, then stick with the 2 12V chargers and monitor yourself once a month (on a maintenance schedule) - Its not fool proof, but will limit your risk. Right way is a decent 24v charger, a battery balancer, and something that will monitor the midpoint in case a cell fails or voltage falls below what you need to start gen.

Manual monitoring will work, but not if it's critical to your environment. Do you take the risk of having to setup/purchase a new battery when offline?

Mine is only a 12V starter, but I have a 48V bank nearby to jumpstart manually if ness, and I also have 2 spare batteries continuously charged, so I can lug into place if needed... Different solution to the issue, but extremely manual and frustrating when I need to use. So not a valid solution to your question.

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PS: And keep a spare also on charge if going manual - nothing you can do late at night or a weekend when no-one open, if a battery is poked... I have about 4 old car batteries around that I manually charge up about 3 times per year, weren't good enough for the cars they where in, but still operational and can deliver about 40A starter current if needed. Use these crappies to even help out when cars have been standing too long.

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1 hour ago, PaulF007 said:

Now that is in my Price range - got a link by any chance 

Got one for my father in law some time ago. They may or may not have them anymore. Can't find it on their website. It looks like a smaller C-tek. It is very likely some cheapie from China.

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9 minutes ago, KLEVA said:

2 seperate chargers connected in series

Nope. One charger is connected to the one battery. The other charger is connected to the other battery. The positive of one battery happens to be at the same potential as the negative of the other, but since the chargers are completely isolated this is of no concern. As long as the bank itself is open circuit on the other end there is no current flow between the two batteries and no need for balancing. They are simply being independently maintained.

Once you have a load on them... then yes... then things become a bit more complex. Then current flows from one battery to the other, and indeed possible also from one charger through the other.

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Another Odd PS and maybe an option to consider: A cheapie Solar Charger can usually handle both 12 & 24 V systems - Maybe consider a cheapie Solar charger (R800 or less) and basic solar panel to keep charge - It's what I do in my van, then NO Eskom/Municipality. Still gonna be a manual system, but then you at least not paying Eskom/Municipality to keep them charged?

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@plonkster - Apologies - I didn't mean the chargers in series, I (in my head) was reffering to the batteries in series... Although, series charger might work as long as it is isolated properly... Just need to test the charger and make sure it doesn't pull to ground/negative... It would have to give a full 24V without making sparks, so apologies if thats what it seemed like I was suggesting, it's a big risk of sparks and earth tripping on cheapie chargers.

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@PaulF007 - Sorry, lot's of options and confusions in my posts, my head sometimes thinks about 20steps faster than I type - My simplest answer now considering your question and the idea to keep it as cheap as possible is as follows:

  • Get a cheap solar charger (almost all can do 24V, just read the specs)
  • Either connect the Solar charger to small low wattage panels (my preference), or feed the controller with "fake" solar power at 18-32V (dependant on the controller above specs, or whatever basic transformer you can find)
  • The solar charger (PWM) will keep the transformer or the solar panels from overcharging/damaging, and will keep the costs as low as I can think to make them

That should solve your issue keeping the batteries charged - It's not fool proof, but might be cheaper than the 24V battery charger.

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If I look at importing then this should do the trick and it is cheap :)
 

It is quite cool to see all the different solutions that we can up with, 

@KLEVA  - 

1 hour ago, KLEVA said:

Cost of a battery balancer + cost of a monitoring device like a BMV702 (you want to watch the midpoint in case a single cell fails in one of the batteries)

This was brilliant !! 

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3 hours ago, PJJ said:

I am sure no expert, but that just sounds like a horrible idea :P

 

3 hours ago, The Terrible Triplett said:

O it works very well.

Believe me, this started of as a test, 2 years ago and this test gave me serious respect for blue. I bought the 75/15 second hand to play with and wanted to see what it will take to blow it. With it still running , I guess I failed....  That 75/15 handled everything I through its way with ease...

I ordered my second one to go in parallel with this one. Was supposed to be delivered today.  I am changing the system a bit but the 48Volt will remain wired as a backup. A flick of a switch and my 48V bank will be supplying these two Mppt's.

3 hours ago, PaulF007 said:

Cool idea but I would like to use AC , 

Why I dont like this way, PV (DC) to AC, AC to Charger back to almost DC. 

From the calculations I did way back, DC to AC to DC conversions had more conversion losses than

DC (PV) > 48V to 48V - 12V

At the time I was trying to see How long I could run my system off grid so every watt counted.  

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I would avoid that kind of generic charger - thats the same as you can buy at a Midas or similar - Absolutely no control or protection - these chargers are definately not for permanent use - they have limited or NO logic.

I like PJJ solution, but would prefer to throw in the forum store. We know the people. But the products/thoughts are the same, and we support our own?... pricey, but obviously the high quality... and supported...
https://powerforum-store.co.za/collections/controllers/products/victron-bluesolar-pwm-light-12-24v-10a
https://powerforum-store.co.za/collections/solar-panels/products/enersol-50-watts

Please remember the 24V spec - You need 28V for that controller in a 24V system so 2 smaller panels would work just as well to keep those batteries charged sufficiently
https://powerforum-store.co.za/collections/solar-panels/products/enersol-20-watts

Edited by KLEVA
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3 minutes ago, Jaco de Jongh said:

Believe me, this started of as a test, 2 years ago and this test gave me serious respect for blue. I bought the 75/15 second hand to play with and wanted to see what it will take to blow it. With it still running , I guess I failed....  That 75/15 handled everything I through its way with ease...

I ordered my second one to go in parallel with this one. Was supposed to be delivered today.  I am changing the system a bit but the 48Volt will remain wired as a backup. A flick of a switch and my 48V bank will be supplying these two Mppt's.

I have no doubt that that would work, I think you missed my post here:

3 hours ago, PJJ said:

Oops, I see I  didn't qoute the OP, I was talking about the chargers 2 12V chargers in series.

 

3 minutes ago, KLEVA said:

I like PJJ solution, but would prefer to throw in the forum store. We know the people. But the products/thoughts are the same, and we support our own?... pricey, but obviously the high quality... and supported...

No problem with that, local is lekker as they say :)

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