Hi, I'd like a 10kW 48V DC instant water heater. Just like this Stiebel-Eltron product but 48V DC. I'm pretty sure this doesn't exist as a commercial product, but could someone build me one?

 

Is your power supply capable of providing over 200 amps?

\(I=\frac{P}{V}=\frac{10KW}{48V}=208A\)

Are you competent to work with high power?

 

My power supply is a 57kWh lithium battery bank, so 10kW is less than 0.2C, so should be fine (lithium batteries can usually safely be discharged at about 0.4C).

> Are you competent to work with high power?

Nope! But will get some help from someone who is before turning this system on.

 

My power supply is a 57kWh lithium battery bank, so 10kW is less than 0.2C, so should be fine (lithium batteries can usually safely be discharged at about 0.4C).

> Are you competent to work with high power?

Nope! But will get some help from someone who is before turning this system on.

KWh and KW are two different things. You need to know how much current your battery can provide.

 

The "C" rating of a battery means the power that would be provided if the battery was fully drained in one hour - e.g. 1C = 57kW, and 0.2C = 11.4kW for this battery:

https://batteryuniversity.com/learn/article/what_is_the_c_rate

 

The "C" rating of a battery means the power that would be provided if the battery was fully drained in one hour - e.g. 1C = 57kW, and 0.2C = 11.4kW for this battery:

https://batteryuniversity.com/learn/article/what_is_the_c_rate

I know what C means, do you know what KWh means? It's not a different way of spelling KW.

 

Yes, but 1C for a 57kWh battery is 57kW... right?

 

Yes, but 1C for a 57kWh battery is 57kW... right?

The actual ability for the battery to deliver current is more complex than a simple C rating. You need to know things like ESR which will limit the delivery and derating due to heating. That simple conversion is just an estimate.

You need to know if the battery you want to use to generate 200A for a period as long as the heating element will need to run.

 

Just to be clear, that is a lot of current.

 

These are the cells I'm using... This spec page lists 0.5C as the max discharge current:

https://www.evlithium.com/hot-lithium-battery/946.html

... so I'm confident that the battery pack I'm using will easily supply 10kW for the duration that it's needed...

Here's some chat about someone with basically the same battery pack as mine (4 x 1P16S) talking about internal resistance and heating... sounds like it's not a big issue: https://diysolarforum.com/threads/heat-build-up-at-0-125c-discharge-rate.13907/

 

These are the cells I'm using... This spec page lists 0.5C as the max discharge current:

https://www.evlithium.com/hot-lithium-battery/946.html

... so I'm confident that the battery pack I'm using will easily supply 10kW for the duration that it's needed...

Here's some chat about someone with basically the same battery pack as mine (4 x 1P16S) talking about internal resistance and heating... sounds like it's not a big issue: https://diysolarforum.com/threads/heat-build-up-at-0-125c-discharge-rate.13907/

The battery may be able to handle it, though I am not sure about long term. Another consideration is that you will need to run something like 2/0 AWG wire to the heating element. If you were running 480V you'd only need 20A and the conductors would be a much more reasonable size.

Whatever you do, PLEASE, be very careful and make sure the margins for safety are large. You are thinking about playing with a LOT of current. Make sure you get someone who knows such things to vet all of it.

 

What do you propose to use as the heating element(s)?

 

No idea... Was looking for suggestions really!

 

Whatever you use is going to be very expensive. In theory you could parallel a load of mains-rated 2kW immersion heaters. At 240V rating you'd need 25 x 5 = 125 to get 10kW at 48V !!!. Not very practical .

 

These are the cells I'm using... This spec page lists 0.5C as the max discharge current:

https://www.evlithium.com/hot-lithium-battery/946.html

... so I'm confident that the battery pack I'm using will easily supply 10kW for the duration that it's needed...

Here's some chat about someone with basically the same battery pack as mine (4 x 1P16S) talking about internal resistance and heating... sounds like it's not a big issue: https://diysolarforum.com/threads/heat-build-up-at-0-125c-discharge-rate.13907/

Those cells you link to have a 280Ah capacity (at 0.5C). Running them at 200A will give just over an hour's worth of current at rated voltage - assuming you get everything together...
Also, that 280Ah rating is to a point where the cells drop to 2.5V, after which the battery is basically drained. That means your 3.2Vx15 = 48V will quickly become 2.5Vx15 = 37.5V. And, current will drop (as will the 10kW heat)

 

No idea... Was looking for suggestions really!

https://www.amazon.com/DERNORD-Foldback-Element-Immersion-Electric/dp/B018S4AO8W

Expensive is realative. I think the batteries will cost more.

Bob

 

I'll try to save you some time. Look for somebody who has already done this. If you can't buy it now, you probably won't be able to get it unless you are NASA. There is nothing ordinary about your request.

 

48 volts is an uncommon voltage for heating elements. 12V, 120V, 208V, and 240V immersion heating elements are off the shelf parts. Calculate the resistance of a few readily available heating elements and see if you can assemble them in a series/parallel arrangement that suits your needs.

Or just use a photovoltaic inverter to obtain 240VAC. I'm assuming by the fact that you *have* such a battery bank at your disposal that this is already part of an existing photovoltaic or peak-shaving system, which begs the question; why bother trying to heat water using DC? If inverter losses are a concern then adding more PV modules to compensate would be a far more economical and less laborious option than embarking on a venture such as this.

 

Those cells you link to have a 280Ah capacity (at 0.5C). Running them at 200A will give just over an hour's worth of current at rated voltage - assuming you get everything together...

The system is composed of four independent 1P16S batteries in parallel... So each battery provides 52A.

 

OK everyone, thanks for all you help. It seems like this will be too difficult / expensive so I'm cancelling this part of the project.