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230V AC to 12V DC Step Down Converter
#1
Hi,

I have put a "power wall" in my RV and now the RV has 230V AC power supply, but I want to get rid of the old 12V battery that is currently running a bunch of stuff, so I need a 2000W 230V AC to 12V DC inverter, I'm currently doing it by using a battery charger charging the 12V battery all the time.

I looked around and can't find a good 2000W 230V AC to 12V DC inverter, if any of you have any idea please let me know.
I also heard that I could just use the battery charger as a 230V AC to 12V DC inverter but I'm not sure if that's a good idea..

And I'm trying to achieve as high efficiency as possible as my RV is 100% off grid.
Any suggestion would be welcomed.

The reason I wanna do it via the 230V AC inverter charger instead of the 48V battery is because the inverter charger has a configurable Low Battery Cut Out protection which I've set to 40V. It would also be pretty cool if this is fixable then I can just get a 48V to 12V DC step down that are everywhere.
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#2
So you going to go from 48v to 230vac and then back to 12v? You do know that 2kw at 12v system. Is ~200a?? Also you waste ton of energy.

Either change to 48v appliances or run 48v to 12vdc. Alot more efficienct Smile
Korishan likes this post
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#3
(03-02-2020, 07:31 PM)clementhk Wrote: Hi,

I have put a "power wall" in my RV and now the RV has 230V AC power supply, but I want to get rid of the old 12V battery that is currently running a bunch of stuff, so I need a 2000W 230V AC to 12V DC inverter, I'm currently doing it by using a battery charger charging the 12V battery all the time.

I looked around and can't find a good 2000W 230V AC to 12V DC inverter, if any of you have any idea please let me know.
I also heard that I could just use the battery charger as a 230V AC to 12V DC inverter but I'm not sure if that's a good idea..

And I'm trying to achieve as high efficiency as possible as my RV is 100% off grid.
Any suggestion would be welcomed.

The reason I wanna do it via the 230V AC inverter charger instead of the 48V battery is because the inverter charger has a configurable Low Battery Cut Out protection which I've set to 40V. It would also be pretty cool if this is fixable then I can just get a 48V to 12V DC step down that are everywhere.

I think you'll find 48v DC -> 12v DC + relay more available/cheaper/power-efficient than 240v -> 12v dc.   For an on/off - you can use a relay with 120/240v coil powered by the Inverter - e.g. when inverter is on, the relay turns on 48v power to the DC - DC step down.
clementhk and Korishan like this post
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#4
(03-02-2020, 08:08 PM)OffGridInTheCity Wrote:
(03-02-2020, 07:31 PM)clementhk Wrote: Hi,

I have put a "power wall" in my RV and now the RV has 230V AC power supply, but I want to get rid of the old 12V battery that is currently running a bunch of stuff, so I need a 2000W 230V AC to 12V DC inverter, I'm currently doing it by using a battery charger charging the 12V battery all the time.

I looked around and can't find a good 2000W 230V AC to 12V DC inverter, if any of you have any idea please let me know.
I also heard that I could just use the battery charger as a 230V AC to 12V DC inverter but I'm not sure if that's a good idea..

And I'm trying to achieve as high efficiency as possible as my RV is 100% off grid.
Any suggestion would be welcomed.

The reason I wanna do it via the 230V AC inverter charger instead of the 48V battery is because the inverter charger has a configurable Low Battery Cut Out protection which I've set to 40V. It would also be pretty cool if this is fixable then I can just get a 48V to 12V DC step down that are everywhere.

I think you'll find 48v DC -> 12v DC  +  relay more available/cheaper/power-efficient than 240v -> 12v dc.   For an on/off - you can use a relay with 120/240v coil powered by the Inverter - e.g. when inverter is on, the relay turns on 48v power to the DC - DC step down.

I think that's doable!
Do you know any relay that would work?
And any recommendation for the 48v DC -> 12v DC? This is what I found.
https://www.daygreen.com/collections/36v...ator-w-acc
https://www.daygreen.com/products/36v-48...2663564335


Thanks!!
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#5
(03-02-2020, 08:24 PM)clementhk Wrote:
(03-02-2020, 08:08 PM)OffGridInTheCity Wrote:
(03-02-2020, 07:31 PM)clementhk Wrote: Hi,

I have put a "power wall" in my RV and now the RV has 230V AC power supply, but I want to get rid of the old 12V battery that is currently running a bunch of stuff, so I need a 2000W 230V AC to 12V DC inverter, I'm currently doing it by using a battery charger charging the 12V battery all the time.

I looked around and can't find a good 2000W 230V AC to 12V DC inverter, if any of you have any idea please let me know.
I also heard that I could just use the battery charger as a 230V AC to 12V DC inverter but I'm not sure if that's a good idea..

And I'm trying to achieve as high efficiency as possible as my RV is 100% off grid.
Any suggestion would be welcomed.

The reason I wanna do it via the 230V AC inverter charger instead of the 48V battery is because the inverter charger has a configurable Low Battery Cut Out protection which I've set to 40V. It would also be pretty cool if this is fixable then I can just get a 48V to 12V DC step down that are everywhere.

I think you'll find 48v DC -> 12v DC  +  relay more available/cheaper/power-efficient than 240v -> 12v dc.   For an on/off - you can use a relay with 120/240v coil powered by the Inverter - e.g. when inverter is on, the relay turns on 48v power to the DC - DC step down.

I think that's doable!
Do you know any relay that would work?
And any recommendation for the 48v DC -> 12v DC? This is what I found.
https://www.daygreen.com/collections/36v...ator-w-acc
https://www.daygreen.com/products/36v-48...2663564335


Thanks!!
For 2000w of 48vdc to 12vdc - the links above seem 'about what I would expect' for pricing. 

2000w/48v = 42a going into the 48vdc side of the step-down.  So you'd need a relay with contactors that can handle 50a -  a quick google of "50a contactor 240v coil relay" turn up this....     https://www.spadepot.com/Contactor-DP-240V-50A-DPC50-240-P7689C179.aspx

Relay's are pretty straight-forward - so any would do as long as the contactors can handle the 50a.
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#6
Are you sure you need 2000W at 12V?
If you had a 12V system with your inverter to 230VAC connected to that battery, then sure, 2000W could be used.
You have your 230VAC inverter on the new 48V pack now right?
Most other 12V items don't use nearly that much juice!
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#7
(03-02-2020, 09:29 PM)OffGridInTheCity Wrote: For 2000w of 48vdc to 12vdc - the links above seem 'about what I would expect' for pricing. 

2000w/48v = 42a going into the 48vdc side of the step-down.  So you'd need a relay with contactors that can handle 50a -  a quick google of "50a contactor 240v coil relay" turn up this....     https://www.spadepot.com/Contactor-DP-240V-50A-DPC50-240-P7689C179.aspx

Relay's are pretty straight-forward - so any would do as long as the contactors can handle the 50a.

Were you referring to that contactor for the DC side, or the AC side? That contactor is for AC only. If you try to use it for DC at 50A, it'll burn the contactor pads after awhile, or fuse them together.
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#8
(03-02-2020, 11:06 PM)Korishan Wrote:
(03-02-2020, 09:29 PM)OffGridInTheCity Wrote: For 2000w of 48vdc to 12vdc - the links above seem 'about what I would expect' for pricing. 

2000w/48v = 42a going into the 48vdc side of the step-down.  So you'd need a relay with contactors that can handle 50a -  a quick google of "50a contactor 240v coil relay" turn up this....     https://www.spadepot.com/Contactor-DP-240V-50A-DPC50-240-P7689C179.aspx

Relay's are pretty straight-forward - so any would do as long as the contactors can handle the 50a.

Were you referring to that contactor for the DC side, or the AC side? That contactor is for AC only. If you try to use it for DC at 50A, it'll burn the contactor pads after awhile, or fuse them together.
According to the info, that's 2000w/48vdc = 42a to be turned on/off as input to the 48vdc -> 12vdc step-down unit.  So the contactors (of the relay) need to be able to handle 42a dc - e.g. suggesting 50a (dc) contactor with a 240v coil should be available with some searching. I agree it can be a bit unclear as to 50a ac vs dc as they don't specify a lot of the time - but for example this one seems to suggest dc - https://www.ato.com/50-amps-ac-contactor - as down in the description it says "....The contactor can be divided into an AC contactor and a DC contactor according to the type of the controlled current. ...". I've had good luck finding a physical relay (indoor/outdoor, I like it's mounting method, its wire hookup method etc) and then contact the manufacturer to confirm 50a ?? (ac or dc and anything else) and get help ordering the exact model number.
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#9
(03-02-2020, 10:14 PM)Redpacket Wrote: Are you sure you need 2000W at 12V?
If you had a 12V system with your inverter to 230VAC connected to that battery, then sure, 2000W could be used.
You have your 230VAC inverter on the new 48V pack now right?
Most other 12V items don't use nearly that much juice!

It's a RV, I have heater, fridge, lights, etc running on it.
I just checked and it's actually 1200W according to the fuses.

(03-03-2020, 01:58 AM)OffGridInTheCity Wrote:
(03-02-2020, 11:06 PM)Korishan Wrote:
(03-02-2020, 09:29 PM)OffGridInTheCity Wrote: For 2000w of 48vdc to 12vdc - the links above seem 'about what I would expect' for pricing. 

2000w/48v = 42a going into the 48vdc side of the step-down.  So you'd need a relay with contactors that can handle 50a -  a quick google of "50a contactor 240v coil relay" turn up this....     https://www.spadepot.com/Contactor-DP-240V-50A-DPC50-240-P7689C179.aspx

Relay's are pretty straight-forward - so any would do as long as the contactors can handle the 50a.

Were you referring to that contactor for the DC side, or the AC side? That contactor is for AC only. If you try to use it for DC at 50A, it'll burn the contactor pads after awhile, or fuse them together.
According to the info, that's 2000w/48vdc = 42a to be turned on/off as input to the 48vdc -> 12vdc step-down unit.  So the contactors (of the relay) need to be able to handle 42a dc - e.g. suggesting 50a (dc) contactor with a 240v coil should be available with some searching.    I agree it can be a bit unclear as to 50a  ac vs dc as they don't specify a lot of the time - but for example this one seems to suggest dc - https://www.ato.com/50-amps-ac-contactor  -  as down in the description it says "....The contactor can be divided into an AC contactor and a DC contactor according to the type of the controlled current. ...".    I've had good luck finding a physical relay (indoor/outdoor, I like it's mounting method, its wire hookup method etc) and then contact the manufacturer to confirm 50a  ??  (ac or dc and anything else) and get help ordering the exact model number.

I found a few DC ones on the website you provided, but it has more pole, can I use a 3 pole contactor here?
https://uk.rs-online.com/web/p/contactors/8175020/
What does that 3 pole mean?
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#10
I'm thinking it might make sense to split up your loads eg
- get the low amps items onto one smaller converter & use a low voltage cutout to switch that on/off
- for the high load gear, if you really want to switch it, you need to be looking for an EV (electric vehicle) type contactor with precharge. Note regular automotive & marine ones are usually only rated for max 32VDC, you've got approx 50+ volts from a full "48V" pack. If you're lucky, some gear goes up to 60V.
- low voltage on/off control of the large inverter would be a much better way to do it (if you can find a way to control your inverter this way)
- also note connecting a big inverters input to batteries is an exciting time because of inrush currents, you'll get a massive "splat" spark as you connect,
- also think about a delay so after low volts tripped, it won't reconnect for a bit or you will get a nasty on/off/on/off... oscillation happening.
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