230V AC to 12V DC Step Down Converter

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clementhk

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Feb 12, 2020
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14
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 2000W230V AC to 12V DC inverter, I'm currently doing it by using a battery charger chargingthe 12V battery all the time.

I looked around and can't find a good 2000W230V AC to 12V DCinverter, if any of you have any idea please let me know.
I also heard that I could just use the battery charger as a[size=small][size=small][size=small]23[/size][/size][size=small][size=small]0V AC to 12V DC[/size][/size][size=small][size=small]inverter but I'm not sure if that's a good idea..[/size][/size][/size]

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.
 
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 :)
 
clementhk said:
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 2000W230V AC to 12V DC inverter, I'm currently doing it by using a battery charger chargingthe 12V battery all the time.

I looked around and can't find a good 2000W230V AC to 12V DCinverter, if any of you have any idea please let me know.
I also heard that I could just use the battery charger as a[size=small][size=small][size=small]23[/size][/size][size=small][size=small]0V AC to 12V DC[/size][/size][size=small][size=small]inverter but I'm not sure if that's a good idea..[/size][/size][/size]

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.
Click to expand...


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 arelay 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.
 
OffGridInTheCity said:
clementhk said:
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 2000W230V AC to 12V DC inverter, I'm currently doing it by using a battery charger chargingthe 12V battery all the time.

I looked around and can't find a good 2000W230V AC to 12V DCinverter, if any of you have any idea please let me know.
I also heard that I could just use the battery charger as a[size=small][size=small][size=small]23[/size][/size][size=small][size=small]0V AC to 12V DC[/size][/size][size=small][size=small]inverter but I'm not sure if that's a good idea..[/size][/size][/size]

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.
Click to expand...


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 arelay 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.
Click to expand...


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/collection...c-step-down-converter-voltage-regulator-w-acc
https://www.daygreen.com/products/3...rter-voltage-regulator?variant=11912663564335


Thanks!!
 
clementhk said:
OffGridInTheCity said:
clementhk said:
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 2000W230V AC to 12V DC inverter, I'm currently doing it by using a battery charger chargingthe 12V battery all the time.

I looked around and can't find a good 2000W230V AC to 12V DCinverter, if any of you have any idea please let me know.
I also heard that I could just use the battery charger as a[size=small][size=small][size=small]23[/size][/size][size=small][size=small]0V AC to 12V DC[/size][/size][size=small][size=small]inverter but I'm not sure if that's a good idea..[/size][/size][/size]

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.
Click to expand...


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 arelay 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.
Click to expand...


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/collection...c-step-down-converter-voltage-regulator-w-acc
https://www.daygreen.com/products/3...rter-voltage-regulator?variant=11912663564335


Thanks!!
Click to expand...

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.
 
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!
 
OffGridInTheCity said:
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.
Click to expand...

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.
 
Korishan said:
OffGridInTheCity said:
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.
Click to expand...

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.
Click to expand...
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) contactorwith 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.
 
Redpacket said:
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!
Click to expand...

It's a RV, I have heater, fridge, lights, etc running on it.
I just checked and it's actually1200W according to the fuses.

OffGridInTheCity said:
Korishan said:
OffGridInTheCity said:
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.
Click to expand...

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.
Click to expand...
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) contactorwith 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.
Click to expand...

I found a few DC oneson 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?
 
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.
 
clementhk said:
https://uk.rs-online.com/web/p/contactors/8175020/
What does that 3 pole mean?
Click to expand...

3 pole means 3 phase. If you look at the front, it shows L1, L2, L3. L = Line.

You can use a 3 pole contactor and not use it for 3 phase. Let's say you have 1 input and 3 output, for example. but you want power to disconnected all at once if any of the one legs has an issue. This would be similar to a mains breaker that pops disconnect a whole panel if a major enough event occurs.
Problem is, you wouldn't be able to individually disconnect lines unless they went through a second contactor/breaker (which could be done w/o issues as well)
 
3 pole doesnt necesary have to be 3 phases but actually 3 different isolated contacts.

For instance you buy 2 pole to accomondate full isolation of battery and you get 4 pole for full isolation of 3phase systems ;)
 
Redpacket said:
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.
Click to expand...

Thanks, I'll look into splitting up my load.

Korishan said:
clementhk said:
https://uk.rs-online.com/web/p/contactors/8175020/
What does that 3 pole mean?
Click to expand...

3 pole means 3 phase. If you look at the front, it shows L1, L2, L3. L = Line.

You can use a 3 pole contactor and not use it for 3 phase. Let's say you have 1 input and 3 output, for example. but you want power to disconnected all at once if any of the one legs has an issue. This would be similar to a mains breaker that pops disconnect a whole panel if a major enough event occurs.
Problem is, you wouldn't be able to individually disconnect lines unless they went through a second contactor/breaker (which could be done w/o issues as well)
Click to expand...

Thanks, if I only use one of the 3pole, can the load still go up to 80A on this contactor?
 
300VDC @ 80A is the max each of the contacts can handle. so yeah, each contact can do 80A. Also, you can drop voltage and increase amp rating. So halving the voltage to 150VDC won't double the amps to 160A. You are still limited to 80A.
 
Use these in parallel :
https://secondlifestorage.com/showthread.php?tid=8065

The idle losses are about 7W each and you can stack up as many as you want in parallel for higher amps because they are fully isolated.

Don't solder to them and try to get the crimp terminal plugs to fit.

The units can be switched on and off with a few mA between two pins... however the supply for each board would need a separate fuse.

Also with a 3 pole breaker you can just use all 3 contacts in parallel, so if you have an 80A breaker, wire all 3 in paralle and you get 240A. BUT...... beware that the contacts need to be good as you can end up with one pole thermally tripping the device early. For example if you end up with 60A, 60A, 90A flowing. the third pole at 90A will try to trip the device.

I have used some cheap 4 pole DC breakers in paralle with copper busbars (consumer / fuse unit bars) to cross connect the poles. Using lower amp rated poles in parallel eases contact isseus, like using a 4 pole 20A breaker in paralell for a 80A supply.
 
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