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Safety Concerns for 48V Battery in RV

Ceefiveceefive

Ceefiveceefive

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Sep 28, 2019
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Hello all! I now have two 48V - 9.6kWh LG Powerwall Systems from BigBattery. I am going to put them into parallel for some nice storage!
I will use these with the new 6048 Inverter System from MPP.

I am brand new to 48V systems as this will be my first install into my RV. I understand that getting into 48V has more danger than 24V & 12V.

What are safety concerns I ought to be aware of?
Does anyone have suggestions / no-no's as to how I can use these safely?
 
Weight is the one I would be concerned about. RVs don’t really have all the cargo weight because the water weight gets subtracted from this cargo weight. I get 5.3 KW with four golf cart FLA batteries, and that weighs about 300 LBS.

Another thing I’m struggling with is how to power efficiently the 12 volt items I have. I have very little 12 volt draw except when I run the propane heater and the blower motor kicks on. I’ve seen my leveling jacks draw 50 amps, and others have seen 100 amps or 200 amps. Those ranges are beyond what I’ve found for 24 volt to 12 volt DC converts and now a 12 volt battery needs to stay in the system and now its an additional charger.
 
I'm in a similar boat. I'm adding a 48V Lithium battery + solar + inverter system to an RV with an existing 12 Lead Acid system. Some of the gear on the RV draws from 12V and I want to keep those batteries charged from the 48V pack.

Most DC -> DC converters that I've seen are meant for supplying 12v and thus are tuned for low-12V and won't effectively keep the Lead battery bank charged. Would it make sense to just run a 12V battery charger that's plugged into the 120v system? All the ones I'm seeing just have alligator clips and seem to be intended for short term usage.
 
Victron does not make a 48 volt to 12 volt DC charger. The 24 volt to 12 volt charger wears hard enough to find.

Only 24 volt to 12 volt chargers. One thing I’m wondering is how efficient that is, especially since most of my energy is 12 volt. I‘d probably lose 15%, but I need to look more. I woud think a 120 volt charger would be really inefficient, maybe another 15% With the DC to AC back to DC.

If you do go that route, the alligator clips can be removed and ring terminals added, but the better battery chargers I’ve seen have a removable clamps where you can attach ring terminals, at least on the 12 volt and 24 volt.

You would think a 48 volt to 12 volt charger is put there and that you’d not be the first to try it. The two things on my trailer that need a 12 volt battery and not converter are a breakaway trailer brake and also the leveling system. Maybe the brake can be done off a converter, I don’t know. In a pinch the leveling can be done manually, but its not an easy thing to do.
 
Why wouldn't a small 12 v charger and a smallish 12V lead acid battery as your 12V "surge" bank be the most cost effective and elegant solution for intermittent loads like leveling jacks, vs a massive 48-12V DC-DC?
 
Quoted from elsewhere
“ The IEC defines 'Safe Extra Low Voltage' (SELV) as DC less than 50V. This is because 50 volts is generally not enough to penetrate the (intact) skin of a human. You could touch the contacts of a 48V battery without getting a shock. However, if you have a cut, or there's a sharp point on one of them that pierces your skin, all bets are off. Still, electrical shock usually isn't dangerous until there's a current path through your heart. (only touch with one hand).”

The big problem with the kind of low voltage systems discussed on this board is the large amounts of stored power. If these discharge in an uncontrolled way then it’s certainly not safe!

Shorts are the way uncontrolled discharge primarily happens. This can be vibration damaged wires or tools accidentally touching the wrong bits

Safety tips

Design your system with correct fusing/breakers and wire sizing. Fuses protect the wires from being over loaded through shorting.

Use insulated tools where possible (minimal exposed metal). Electricians screwdrivers are typically insulated (plastic covered) so that just the tip is exposed. Plenty of people on here use shrink wrap or insulating tape to insulate socket wrenches and spanners.

Make sure all connections are put together correctly and are tight enough. Poor connections don’t conduct electricity properly so can become hot and there fire a risk.

Be wary of working in hot confined spaces. Sweaty arms conduct power uncomfortably ?

Code should be the minimum safety standard applied ?

48V is very unlikely to kill you via electric shock

Hope this helps
 
Trabuco said:
Why wouldn't a small 12 v charger and a smallish 12V lead acid battery as your 12V "surge" bank be the most cost effective and elegant solution for intermittent loads like leveling jacks, vs a massive 48-12V DC-DC?
Click to expand...
Which smallish 12 volt charger do you have in mind? I am having trouble finding DC to DC chargers, and I did not find 48 volt to 12 volt charger. I found one 24 volt to 12 volt charger for Victron I'd use. If there's a smallish charger I'm missing, please point me in the correct direction.
 
ianganderton said:
Quoted from elsewhere
“ The IEC defines 'Safe Extra Low Voltage' (SELV) as DC less than 50V. This is because 50 volts is generally not enough to penetrate the (intact) skin of a human. You could touch the contacts of a 48V battery without getting a shock. However, if you have a cut, or there's a sharp point on one of them that pierces your skin, all bets are off. Still, electrical shock usually isn't dangerous until there's a current path through your heart. (only touch with one hand).”

The big problem with the kind of low voltage systems discussed on this board is the large amounts of stored power. If these discharge in an uncontrolled way then it’s certainly not safe!

Shorts are the way uncontrolled discharge primarily happens. This can be vibration damaged wires or tools accidentally touching the wrong bits

Safety tips

Design your system with correct fusing/breakers and wire sizing. Fuses protect the wires from being over loaded through shorting.

Use insulated tools where possible (minimal exposed metal). Electricians screwdrivers are typically insulated (plastic covered) so that just the tip is exposed. Plenty of people on here use shrink wrap or insulating tape to insulate socket wrenches and spanners.

Make sure all connections are put together correctly and are tight enough. Poor connections don’t conduct electricity properly so can become hot and there fire a risk.

Be wary of working in hot confined spaces. Sweaty arms conduct power uncomfortably ?

Code should be the minimum safety standard applied ?

48V is very unlikely to kill you via electric shock

Hope this helps
Click to expand...
Thanks! Just the kind of info I was looking for!
 
chrisski said:
Which smallish 12 volt charger do you have in mind? I am having trouble finding DC to DC chargers, and I did not find 48 volt to 12 volt charger. I found one 24 volt to 12 volt charger for Victron I'd use. If there's a smallish charger I'm missing, please point me in the correct direction.
Click to expand...
1st one I pulled up. Not sure what smallish vs your budget looks like, but here's a 96V input rated solar charge controller for less than sixty bucks that will deliver any number of lead acid 12V charge profiles, including sealed, flooded, and AGM.

Looks like it will charge your phone and keep the lights running, too. ;)

Use your 48V system to feed the solar input. Dig deeper into ebay, and I'm sure you'll find many more at cheaper prices.

 
Last edited:
Trabuco said:
1st one I pulled up. Not sure what smallish vs your budget looks like, but here's a 96V input rated solar charge controller for less than sixty bucks that will deliver any number of lead acid 12V charge profiles, including sealed, flooded, and AGM.
Click to expand...
What a brilliant idea. A charge controller from a 48 volt battery bank to a 12 volt battery bank. I never thought of using a charge controller and was hooked at "must find DC to DC Charger." Seems like a brilliantly simple idea, becasue what is a solar charge controller besides a DC to DC charger? This makes limitless choices now. Thanks.
 
It took me a minute to come up with something that would shoot holes in the idea of using a solar charge controller instead of a DC-DC charger. The solar charge controller is going to keep pulling power out of the 48v battery forever. The DC-DC charger can be configured to stop pulling power at X volts (as seen from the source battery).

Victron has the Orion Tr 48/12-9 charger.
 
HRTKD said:
It took me a minute to come up with something that would shoot holes in the idea of using a solar charge controller instead of a DC-DC charger. The solar charge controller is going to keep pulling power out of the 48v battery forever. The DC-DC charger can be configured to stop pulling power at X volts (as seen from the source battery).

Victron has the Orion Tr 48/12-9 charger.
Click to expand...
The one I linked to transitions to float charging with a “the charging current almost be zero when controller is floating charge” note.

I wonder what the draw is in float mode. Might be quite low. As a “solar” charger it “should” be designed to be efficient.

It can’t pull significant amounts of power forever if it’s got no where to deliver them, unless it is just radiating heat. It is just a specialty DC-DC converter.
 
A solar charger uses a limited current input, the value of the panel. Would you have to limit available amps in from the battery to stop it from destroying itself?
Just a thought.....
 
HRTKD said:
The DC-DC charger can be configured to stop pulling power at X volts (as seen from the source battery).

Victron has the Orion Tr 48/12-9 charger.
Click to expand...
Much better idea than the SCC. I still think the SCC is a good idea, but not going to be the first on my block to try it, especially with one from a reputable company available. Also months and lots of $ has went into this 12 volt build, so why risk it?

I skipped over it because it says converter, but the tech sheet says it charged a 12volt or 24 volt battery.
 
Daniel Beardsley said:
I'm in a similar boat. I'm adding a 48V Lithium battery + solar + inverter system to an RV with an existing 12 Lead Acid system. Some of the gear on the RV draws from 12V and I want to keep those batteries charged from the 48V pack.

Most DC -> DC converters that I've seen are meant for supplying 12v and thus are tuned for low-12V and won't effectively keep the Lead battery bank charged. Would it make sense to just run a 12V battery charger that's plugged into the 120v system? All the ones I'm seeing just have alligator clips and seem to be intended for short term usage.
Click to expand...
Maybe it's obvious to others but I'm going to ask anyway; why not use a bucky converter? It can take any higher voltage, and provide reliable and steady voltage on the output as long as it's a lower voltage. IE it can easily and efficiently convert 48v to 12v. Would that not be the simplest solution?
 
Kodack said:
Maybe it's obvious to others but I'm going to ask anyway; why not use a bucky converter? It can take any higher voltage, and provide reliable and steady voltage on the output as long as it's a lower voltage. IE it can easily and efficiently convert 48v to 12v. Would that not be the simplest solution?
Click to expand...

My thought on that solution is that the buck converter is likely to provide a constant voltage/constant current to the 12v battery, which may not be ideal for the longevity of the 12v battery.
 
HRTKD said:
My thought on that solution is that the buck converter is likely to provide a constant voltage/constant current to the 12v battery, which may not be ideal for the longevity of the 12v battery.
Click to expand...
Oh you want to charge a 12v battery off 48v, not run a 12v appliance? I was thinking you wanted to remove the 12v battery and just buck convert down to 12 for your accessories. Less points of failure.

For charging a 12v battery off 48v you'd just need a DC/DC battery charger. They are fairly common, just make sure the input voltage works from up to 48v. The main thing is you just want to avoid any kind of linear regulators as they create waste heat and are inefficient.
 
Kodack said:
Oh you want to charge a 12v battery off 48v, not run a 12v appliance? I was thinking you wanted to remove the 12v battery and just buck convert down to 12 for your accessories.
Click to expand...

Not me. I'm not the OP of this thread. I'm the guy offering constructive criticism.
 
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