Do I need another BMS after a step down converter

[bds70]

Hi, I am going to build a 48v battery for my updated setup. However I also need a small 12v battery for my 12v appliances.

Using a step down 48/12 converter will I still need a BMS in the 12v battery?

 

[Partimewages]

If you're going to a 12 volt lifepo4 battery then yes.

 

[bds70]

If you're going to a 12 volt lifepo4 battery then yes.

Thanks. Glad I thought to ask

 

[bds70]

If you're going to a 12 volt lifepo4 battery then yes.

Just a thought, U said "if", would that mean I could use a gel hybrid 12v, without a bms as I happen to have 1 hanging about?

 

[Partimewages]

Yes, just watch the charge parameters for it. It has to be totally isolated from the Lifepo4 bank. You can't combine chemistries.

 

[Skypower]

How much current do you need at 12volts?
These are great if you don’t need much current. They have almost nil standby current, highly efficient under load and extremely clean output. Only $30

https://a.co/d/4tMzVY5

 

[bds70]

The biggest load is the macerator motor at 18amps. The other 12v stuff is minimal, led lights, water pump, and a couple of extraction fans. So I reckon that would do.

 

[bds70]

Yes, just watch the charge parameters for it. It has to be totally isolated from the Lifepo4 bank. You can't combine chemistries.

The converter would achieve that isolation?

 

[Partimewages]

The converter would achieve that isolation?

Yes, but check the min/max voltage on the 12 volt side. I don't know if it fluctuates with the 48v side.

 

[Skypower]

The biggest load is the macerator motor at 18amps. The other 12v stuff is minimal, led lights, water pump, and a couple of extraction fans. So I reckon that would do.

The macerator may be too much for that. 18 amps is probably the running current not the inrush to start or minor jam.

 

[Partimewages]

@Lt.Dan don't you use a 48v to 12v converter?

 

[Skypower]

The converter would achieve that isolation?

The converter that I showed is Not isolated. The two negatives show continuity. You’d have to step up to a Victron dc-dc converter/charger for that. Good but not cheap.

 

[Partimewages]

Victron has new Orion models coming this year.

 

[Lt.Dan]

@Lt.Dan don't you use a 48v to 12v converter?

I used to use a 100a Daygreen model on my last RV. I am currently using a 40a model like the one posted above and it works great.

If the 12v loads do not exceed 20-30a, then using a converter like posted above, without a battery, is a very viable option.

 

[bds70]

The macerator may be too much for that. 18 amps is probably the running current not the inrush to start or minor jam.

Lol, not saying anything, but ....... Haha
But a 30 amp converter should be enough to handle that. Maybe I need to create a jam, and run the clamp meter on that circuit see what it pulls.

"hey wife, can you cook your ma's meat loaf tonight?"

 

[bds70]

Victron has new Orion models coming this year.

Yeah very expensive though

 

[bds70]

I used to use a 100a Daygreen model on my last RV. I am currently using a 40a model like the one posted above and it works great.

If the 12v loads do not exceed 20-30a, then using a converter like posted above, without a battery, is a very viable option.

Hadn't thought of that, so you would connect the terminals direct to a fuse distribution box, that I already have? Is that right?

 

[Lt.Dan]

Hadn't thought of that, so you would connect the terminals direct to a fuse distribution box, that I already have? Is that right?

Correct, the 12v output of the converter would go direct to fuse block/distribution panel.

Edit: Here is the one I'm currently using: https://www.amazon.com/gp/product/B01MYMVGSU/ref=ppx_yo_dt_b_search_asin_title

 

[bds70]

After all that, I have had to revert to plan A. It's not financially feasible to go the 48v route. Thank you to all who have helped me. I shall now ask some questions on a new thread regarding 12v feeling a bit pissed off. Ah well. Another day another dollar poorer!

 

[Skypower]

I think that if you were going to go with a 30 amp model that you might want to go with the model that Lt.Dan listed. Mine hasn’t been pushed hard and my assumption is that Dan’s has been or better tested. I’ve bought about a dozen of these in different sizes and boost or bucking. There’s at least 6 brands and they look like they all came out of the same factory/mould same sticker just a different name on the label. Perhaps they are that good at stealing each other’s ideas in China. I had only one failure and that was a Supernight boost 12 to 24 10 amp which fell on its face at half load.
Reading though all the reviews the common complaint on all varieties is not holding up under load. Pretty much they fail early or not at all so test yours out under load before the return period runs out. Every buck or boost of this type is not isolated. They make bigger converters but I don’t know how efficient they are.