Why does no one make a generic DC to DC charger for motorhomers?

[urban_biker]

What I'm looking for is a DC device that I can connect to the leisure battery and can produce a range of DC output voltages from around 3V - 50V DC at up to around 500 watts. And includes the ability to attach multple types of output plug.

The idea being that most devices that use 230V AC mains in our motorhomes end up with a large brick power supply that then converts the AC power to some other DC voltage in the range described above. So a system with an inverter ends up converting 12VDC to 230V AC (with inefficiency and heat loss) and then back down to say 18V dc (with inefficiency and heat loss) for a laptop power supply.

It would be great to take the inverter out of the system for most low wattage uses.

Is such a thing possible and does anyone make one?

I know some of the DC to DC battery to battery chargers (E.G Victron Orion) can supply DC up to around 15 V and could easily be configured as a power supply/charger but I'm finding lots of devices that require a higher voltage than that.


What devices could be powered in this way?

For me it would be , Dyson vacum cleaner charging, electric bike charging, laptop power supply/charging.

 

[Langtoftlad]

Scale

 

[urban_biker]

Scale

You mean the small market for such a product means its not viable right? But I'm guessing its technically possible?

 

[chaser]

What I'm looking for is a DC device that I can connect to the leisure battery and can produce a range of DC output voltages from around 3V - 50V DC at up to around 500 watts. And includes the ability to attach multple types of output plug.

The idea being that most devices that use 230V AC mains in our motorhomes end up with a large brick power supply that then converts the AC power to some other DC voltage in the range described above. So a system with an inverter ends up converting 12VDC to 230V AC (with inefficiency and heat loss) and then back down to say 18V dc (with inefficiency and heat loss) for a laptop power supply.

It would be great to take the inverter out of the system for most low wattage uses.

Is such a thing possible and does anyone make one?

I know some of the DC to DC battery to battery chargers (E.G Victron Orion) can supply DC up to around 15 V and could easily be configured as a power supply/charger but I'm finding lots of devices that require a higher voltage than that.


What devices could be powered in this way?

For me it would be , Dyson vacum cleaner charging, electric bike charging, laptop power supply/charging.

Have a look on eBay there are various things like you describe but maybe not big enough.

 

[urban_biker]

Have a look on eBay there are various things like you describe but maybe not big enough.

yes - you can find something that will do part of the spec above but nothing that can do all of it.

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[chaser]

yes - you can find something that will do part of the spec above but nothing that can do all of it.

Maybe join two or more different ones together?
Or perhaps start with one of these power bank things.

 

[Jev88]

Like this? Plug it into your one inverter and it gives you whatever DC out you want ?

Programmable DC Power Supply (0-30 V 0-10 A) High Precision 4-Digit Multiple Protection with PC Software and USB Charging https://www.amazon.co.uk/dp/B0928LX2D1?ref_=cm_sw_r_apan_dp_0YKFW45N0P9GW6AVA57M

 

[poppycamper]

Like this? Plug it into your one inverter and it gives you whatever DC out you want ?

Programmable DC Power Supply (0-30 V 0-10 A) High Precision 4-Digit Multiple Protection with PC Software and USB Charging https://www.amazon.co.uk/dp/B0928LX2D1?ref_=cm_sw_r_apan_dp_0YKFW45N0P9GW6AVA57M

Link no worky... at least nit on my phone..

 

[Jev88]

Link no worky... at least nit on my phone..

Screen shot instead......

 

[tonka]

Google buck converter and the spec you want. Maybe that would do it ?

Amazon product ASIN B0B2111VF6

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[The Wino]

Nowhere near the power output you want but this does several voltages
https://www.ebay.co.uk/itm/19389981...d=link&campid=5338547443&toolid=20001&mkevt=1

 

[Hoovie]

Like this? Plug it into your one inverter and it gives you whatever DC out you want ?

Programmable DC Power Supply (0-30 V 0-10 A) High Precision 4-Digit Multiple Protection with PC Software and USB Charging https://www.amazon.co.uk/dp/B0928LX2D1?ref_=cm_sw_r_apan_dp_0YKFW45N0P9GW6AVA57M

Except .... What I think he wants to do is (for some reason) charge all these various devices that start life with chargers that are essentially AC-DC transformers but have different DC voltage outputs.

So what he will get with the type of device you linked to is a way to use an Inverter to avoid using an Inverter . If the above was an option, he could just use the provided chargers to start with . (which TBH, I don't know why people don't, instead of faffing around with a multitude of DC-DC converters.)


And to answer the original question with a "gotcha" .... imagine you got this super-flexible DC-DC voltage converter/charger and you used it to charge the batteries on your 18V laptop, and your 48V ebike, and your 12V cordless drill... Set it to 48V for the bike. Then plug in the cable for your 12V drill battery. But you forgot to change the voltage! Well, that battery is toast (maybe literally!).

Too many things that can go wrong and damage kit plugged into it to make anyone who would be interested to make one of these actually interested in making one commercially. To be frank, the user base for product like this would be too small and too careless (to always remember to check - OR to even know the voltages).
And I include myself in the latter 'careless' bit. I guarantee if a user had a device like that, they would blow something up within a year (hell, within a month probably!). And who would get the blame and a request to replace the blown up battery?

 

[urban_biker]

Too many things that can go wrong and damage kit plugged into it to make anyone who would be interested to make one of these actually interested in making one commercially. To be frank, the user base for product like this would be too small and too careless (to always remember to check - OR to even know the voltages).
And I include myself in the latter 'careless' bit. I guarantee if a user had a device like that, they would blow something up within a year (hell, within a month probably!). And who would get the blame and a request to replace the blown up battery?

I guess that's probably a key reason. It would have to be fairly fool proof. perhaps a programmable interface with selectable devices that you were able to pre-program for voltage, polarity, connector type and charge profile (if applicable).

But the reason I would like one is fairly sound I think; that the conversion from DC to AC (Inverter) and back again (adaptor block) is wasteful in energy terms. i.e your leisure battery drains much faster than it needs to!

I guess it would be good to have some data on what that impact is.

 

[Gromett]

Except .... What I think he wants to do is (for some reason) charge all these various devices that start life with chargers that are essentially AC-DC transformers but have different DC voltage outputs.

So what he will get with the type of device you linked to is a way to use an Inverter to avoid using an Inverter . If the above was an option, he could just use the provided chargers to start with . (which TBH, I don't know why people don't, instead of faffing around with a multitude of DC-DC converters.)


And to answer the original question with a "gotcha" .... imagine you got this super-flexible DC-DC voltage converter/charger and you used it to charge the batteries on your 18V laptop, and your 48V ebike, and your 12V cordless drill... Set it to 48V for the bike. Then plug in the cable for your 12V drill battery. But you forgot to change the voltage! Well, that battery is toast (maybe literally!).

Too many things that can go wrong and damage kit plugged into it to make anyone who would be interested to make one of these actually interested in making one commercially. To be frank, the user base for product like this would be too small and too careless (to always remember to check - OR to even know the voltages).
And I include myself in the latter 'careless' bit. I guarantee if a user had a device like that, they would blow something up within a year (hell, within a month probably!). And who would get the blame and a request to replace the blown up battery?

I didn't like the idea but didn't know why. Something was nagging at the back of my brain. You got it and reminded me. About 20 years ago I had a universal 12v to xV converter for laptops. Back then I had multiple laptops.
Without thinking I plugged it into my 12V laptop while it was still set to 19V and blew it up.

I do not like universal supplies for this reason. Too easy to have a brain fart and destroy things. Nicely put Hoovie

DC-DC converters are so cheap these days that it is worth getting a dedicated one for each device and hard wiring it.

 

[Hoovie]

I guess that's probably a key reason. It would have to be fairly fool proof. perhaps a programmable interface with selectable devices that you were able to pre-program for voltage, polarity, connector type and charge profile (if applicable).

But the reason I would like one is fairly sound I think; that the conversion from DC to AC (Inverter) and back again (adaptor block) is wasteful in energy terms. i.e your leisure battery drains much faster than it needs to!

I guess it would be good to have some data on what that impact is.

I can fully understand the WHY of why this would be of use to you and others. Using an Inverter to convert DC to AC to only then convert back to DC again is energy-inefficient.
However ... getting an adapter for a Laptop to run off DC (which means a DC-DC conversion is needed, which has its own overheads), and another adapter for an eBike DC charger, and an adapter for a Power Tool DC charger, etc, etc, is pretty financially-inefficient when you already have all these chargers in the form of AC ones.

I would equate the energy-efficency of the AC-DC Charger with its equivalent DC-DC converter you might buy and then the power wastage you have to think of is the Inverter efficiency and overhead. The smaller the inverter, the more efficient it will be for smaller loads (i.e. you don't want to buy a 3000W inverter if you want to power a laptop), and the smaller the load, the higher percentage is wasted on conversion due to overhead (e.g. you turn on an Inverter to power an Amazon Alexa Echo pulling 4W, you will use probably twice that just to have the inverter on).
In my own motorhome, I have converted the very low power devices that come with AC transformers to a DC supply e.g. the Amazon Echos, as I don't want to have my 1350W inverter running just to power stuff that just needs a few watts. But I have an AC Compressor Fridge rather than a DC Compressor Fridge. I will accept the extra 10W Inverter power waste when the compressor calls for power in exchange for saving around £800 on the buy price (as said, taking financial-efficiency over energy efficiency). Middle of the road devices, I have a charger for a 12V battery charger that comes with a 240V-12V transformer, so I just fitted a 12V accessory plug on the lead instead. The Laptops ... just use the normal AC Bricks. Personally, I see little value in spending money on adapters which I don't need if I use the Inverter instead, especially when it gets used for just a few hours a weeks, and will take a few Ahs a week of waste happily.

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[Hoovie]

I didn't like the idea but didn't know why. Something was nagging at the back of my brain. You got it and reminded me. About 20 years ago I had a universal 12v to xV converter for laptops. Back then I had multiple laptops.
Without thinking I plugged it into my 12V laptop while it was still set to 19V and blew it up.

I have a little lithium jump starter kit and it comes with a "universal laptop kit" - bunch of different sized jackplugs, plus a selectable voltage between 12V, 15V, 16V and 19V. Plus ... and this is another gotcha I didn't mention but for a universal kit is another way to break things .... a selectable polarity - as usually the centre pin in a jackplug is the +ve, but sometimes it is the -ve.

As you might imagine, I have NEVER used this laptop charger feature on the Jump Starter kit

I do not like universal supplies for this reason. Too easy to have a brain fart and destroy things. Nicely put Hoovie

DC-DC converters are so cheap these days that it is worth getting a dedicated one for each device and hard wiring it.

 

[urban_biker]

DC-DC converters are so cheap these days that it is worth getting a dedicated one for each device and hard wiring it.

Good point - maybe this is a better way to go or probably even easier to just to live with the inverter loss. Thanks for the discussion!

 

[Gromett]

But I have an AC Compressor Fridge rather than a DC Compressor Fridge. I will accept the extra 10W Inverter power waste when the compressor calls for power in exchange for saving around £800 on the buy price (as said, taking financial-efficiency over energy efficiency).

Someone on here years ago made a modification to a domestic fridge whereby the thermostat was linked to a relay which turned on the inverter. So the inverter wasn't running all the time.

 

[DBK]

I guess that's probably a key reason. It would have to be fairly fool proof. perhaps a programmable interface with selectable devices that you were able to pre-program for voltage, polarity, connector type and charge profile (if applicable).

But the reason I would like one is fairly sound I think; that the conversion from DC to AC (Inverter) and back again (adaptor block) is wasteful in energy terms. i.e your leisure battery drains much faster than it needs to!

I guess it would be good to have some data on what that impact is.

I think you are over-stating the losses in the inverter. We often use ours when not on EHU to recharge the Dyson and the current drawn is negligible and if the sun is shining the 200W solar will also be putting a few amps into the batteries at the same time.

 

[Hoovie]

Some on here years ago made a modification to a domestic fridge whereby the thermostat was linked to a relay which turned on the inverter. So the inverter wasn't running all the time.

The choice of Inverter can be key to efficiency of course.

As an example, I used the Victron Multiplus 12/1600 - that is a 1350W inverter and at Zero Load (i.e. ON but driving nothing), it uses 10-12W (can't recall exactly). So using it to run a 4W device like an Amazon Echo, which would be on all the time (mine is, anyway) would be incredibly inefficient. But set that inverter to AES Search Mode, where it is off, but checks for a load demand every few seconds, the overhead of the inverter drops down to around 2W. That equates to around 2Ah/Day of power, and for me, the convenience of having AC power "on tap" rather than having to actively turn the inverter on when I want to say use the Laptop or the Microwave or whatever is worth that slight overhead.
My Multiplus supplies all the AC outlets in my Motorhome, but if you have an Inverter however that is dedicated to a specific function like yours is, such as a compressor fridge that only needs power around 25% of the time, your approach is for sure the most energy efficient (plus you can also size the inverter specifically for the fridge, whereas my Inverter, while its most common use is for the Fridge is too big ideally for that, as I sized the Multiplus to cope with my largest load, not the most common one)

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[urban_biker]

I think you are over-stating the losses in the inverter. We often use ours when not on EHU to recharge the Dyson and the current drawn is negligible and if the sun is shining the 200W solar will also be putting a few amps into the batteries at the same time.

Yes, probably so. I had a look around for some data and it seems that inverters are around 93 to 96% efficient. Which is pretty impressive really.
230v AC to DC transformers are around 85 to 90% efficient.

And a DC to DC transformer is around 95%.

So overall you are losing around 14% using an inverter combined with an AC transformer ( and most of that loss is coming from the transformer). Vs 5% using just a DC to DC transformer. Probably easier/cheaper/simpler to get a 9% bigger battery and live with the power loss.

 

[Hoovie]

Yes, probably so. I had a look around for some data and it seems that inverters are around 93 to 96% efficient. Which is pretty impressive really.
230v AC to DC transformers are around 85 to 90% efficient.

And a DC to DC transformer is around 95%.

So overall you are losing around 14% using an inverter combined with an AC transformer ( and most of that loss is coming from the transformer). Vs 5% using just a DC to DC transformer. Probably easier/cheaper/simpler to get a 9% bigger battery and live with the power loss.

a extra cost of a 9% bigger battery will likely be cheaper than a host of DC-DC converters And that 9% would be based on the inverter in use 100% of the time AND the only loads are from the Inverter - the actual extra needed is more like 1-2% bigger. Once the maths is done, you realise the losses from an inverter are typically just noise in the overall scheme of things as far as battery usage goes.

PS. the efficiency is linked to the load, remember. The nearer you are to the max rating of the inverter, the more efficient it is in terms of losses (which is why you don't just get the biggest inverter you can find 'just in case' or because it was a good deal).

 

[Gromett]

But set that inverter to AES Search Mode, where it is off, but checks for a load demand every few seconds, the overhead of the inverter drops down to around 2W.

Didn't realise they now did that. My last Multiplus was bought in 2007 and I seem to recall losing around 20-25AH a day with it being on but not in use.

 

[Old Gibber]

So a system with an inverter ends up converting 12VDC to 230V AC (with inefficiency and heat loss) and then back down to say 18V dc (with inefficiency and heat loss) for a laptop power supply.

It would be great to take the inverter out of the system for most low wattage uses.

Basically any electronic device that converts 12v dc to 18v dc still uses an electronic inverter. It converts the dc to a high frequency AC, which then goes through a transformer to be then rectified back to dc again.

 

[Hoovie]

Didn't realise they now did that. My last Multiplus was bought in 2007 and I seem to recall losing around 20-25AH a day with it being on but not in use.

Multiplus from 2007 is before my experience of them so can't be sure if my comments are applicable that far back?
With the current range and ones going back to maybe the last 10 years (or more?), you have to set up the AES mode, and the only way to do that used to be with a PC running VE.Config and Mk3 (or older Mk2) Dongle, so not many end users could configure that. Another way is to connect via VRM if you have a GX device to remove the need for the dongle.

20-25Ah a day sounds about right for an Multiplus left on but unused.

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[autorouter]

You also have to distinguish between a DC-DC converter and a DC-DC charger. A converter just gives you a constant regulated voltage, indefinitely. A charger monitors the battery state and cuts off to avoid overcharging. A DC-DC converter giving 19V is OK for a laptop because the laptop has an inbuilt charger and just needs a 19V supply. However for a 36V ebike battery you need a DC-DC charger that will cut off when the battery is full.

There are any number of DC-DC converters around that will give you any voltage and amps you want. Look on the RS website for example. DC-DC chargers are a bit more difficult to find, apart from standard ones like B2Bs and USB-C

 

[Raul]

Screen shot instead......

View attachment 775954

All of those, require a 230v AC input.

 

[Jev88]

All of those, require a 230v AC input.

Exactly my point. ONE inverter and this box plugs in - allowing you to run any device from this box.

 

[Raul]

Exactly my point. ONE inverter and this box plugs in - allowing you to run any device from this box.

But, we back to power adapters?

 

[Raul]

Multiplus from 2007 is before my experience of them so can't be sure if my comments are applicable that far back?
With the current range and ones going back to maybe the last 10 years (or more?), you have to set up the AES mode, and the only way to do that used to be with a PC running VE.Config and Mk3 (or older Mk2) Dongle, so not many end users could configure that. Another way is to connect via VRM if you have a GX device to remove the need for the dongle.

20-25Ah a day sounds about right for an Multiplus left on but unused.

It can be done via dip switches on the pcb, no need for a mk2-3. And before the multiplus was on phoenix, and before the phoenix was on the Atlas. All with dip switches. On later multiplus the search mode was added, the real AES is totaly diferent to the search mode. AES runs on reduced switching, resulting in less power draw. Search mode cycles every 2s but at full switching, so sine wave is maintained.

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