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24 volt to 12 volt battery charging method?

MKorodini

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Joined
Oct 18, 2021
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Im currently building a 24 volt battery bank in my RV and Im searching for a method to charge the 12 volt batteries used to power the landing gear, slides and lights. I’ve come down to either having the inverter convert it to 110 volts and then have the onboard converter charge the 12 volt batteries. The other method I’m thinking of is to use a 24 to 12 volt dc to dc charger, as this one:
Any input is greatly appreciated.
Apologies if this has already been covered but I haven’t found anything.
 
Last edited:
If you're going to maintain a 12v battery bank, why bother with 24v? That 12v battery bank also has to power your breakaway brake system, assuming we're talking about a trailer and not a motorhome.

Rather than maintain a separate 12v battery system, some forum members are using step down converters that can handle high amp loads. The Victron Orion 24/12-70 is one suggestion. If you go with something like this, be sure it's on while traveling if you need it for the breakaway brake system.
 
If you're going to maintain a 12v battery bank, why bother with 24v? That 12v battery bank also has to power your breakaway brake system, assuming we're talking about a trailer and not a motorhome.

Rather than maintain a separate 12v battery system, some forum members are using step down converters that can handle high amp loads. The Victron Orion 24/12-70 is one suggestion. If you go with something like this, be sure it's on while traveling if you need it for the breakaway brake system.
Thanks for the reply. Im looking to use a growatt all in one inverter. To my knowledge they do not make one for 12 volts, hence the reason for a 24 volt battery bank.
I’ve looked at the step down converter. I would need to use multiple ones to achieve the 250 amps the landing gear can draw. I’ve seen some people have used the step down converter for the lights inside the rig and kept a separate battery for slides and landing gear.
 
I’ve looked at the step down converter. I would need to use multiple ones to achieve the 250 amps the landing gear can draw.
How do you get 250 amps?

My two axle fifth wheel has 50 amps measured on a battery monitor when I raise and lower it. I am installing the Orion 24 volt to 12 volt 70 amp converter for the leveling jacks. If there is some surge which causes the jacks to act odd that the battery monitor can’t pick up, I could put a second converter in parallel with the first.

I hope 250 amps is not that correct. The wiring to these jacks is not that thick.
 
That’s what the sticker on the side is the hydraulic pump says. I haven’t actually measured it myself. I was surprised too. The factory breaker is also a 250amp to the pump.
 
That’s what the sticker on the side is the hydraulic pump says. I haven’t actually measured it myself. I was surprised too. The factory breaker is also a 250amp to the pump.
Just for a sanity check...
This is a 12 volt pump, confirm?
What size wire is going to/coming from the pump?
 
It is a 12 volt pump. I believe it’s a 4awg wire. Ill check once I’m back to my rig.
4 awg wire with 105C insulation is only rated for 160 amps in free air.
But still, its 4 awg wire which suggests that the pump draws serious current.
More than the feeder circuit for most power centers.
 
I feel like I am missing something in your original question as to why you are questioning ac or dc as a source. The growatt has two inputs if it is like mine, solar and 120v ac. The chargers in them will put out a good bit of current (I think 60 amp for that size if i recall, maybe 40) from either the solar or incoming 120v substantially more than the buck boost transformer and its built in. I dont understand why would you want to use a buck boost transformer with the built in charger already, is it your electrical source (ac vs dc?)? If you are using them in series probably best to charge them in series. Make sure that they both of your batteries are the same capacity and at the same state of charge prior to starting. LifePo4 or SLA? You might want to look at something like the battery balancer that watts247 offers. I found inbalance overall to be a limitation in building larger lithium batteries with 280ah cells by breaking them into 12V versions with individual BMS to be moveable and still use them in a 48V series configuration. Once one battery hits full charge it shuts down the whole charging system. The balancer will act as a shunt to balance and charge the series battery bank as a whole if they become imbalanced.
 
In typical fashion for me I’ll ask the question: is there any reason why you can’t run a single 12V deep cycle and a 100W panel with pwm like https://www.amazon.com/dp/B00JML23X0/ref=cm_sw_r_cp_api_glt_fabc_E99XDCJP80VR6MPP2HX3 and keep that for non-inverted loads like the jack? (Price though- I paid $185 for this brand with two 100W panels 3-4 years ago!)

Then you have the best of two worlds and redundancies for lights. Separate the converter charge for that circuit with a switch? I’m guessing you are more than smart enough to get that going lol

Had you considered this? Especially since you probably have an RV lead acid now? With light responsible use and monthly acid level check the lead acid battery could go for 5 or more years. That WindyNation pwm did very well for me; it is clonie looking but from others that look like it I suspect it is a grade above or different- menus are great.
 
4 awg wire with 105C insulation is only rated for 160 amps in free air.
But still, its 4 awg wire which suggests that the pump draws serious current.
More than the feeder circuit for most power
I feel like I am missing something in your original question as to why you are questioning ac or dc as a source. The growatt has two inputs if it is like mine, solar and 120v ac. The chargers in them will put out a good bit of current (I think 60 amp for that size if i recall, maybe 40) from either the solar or incoming 120v substantially more than the buck boost transformer and its built in. I dont understand why would you want to use a buck boost transformer with the built in charger already, is it your electrical source (ac vs dc?)? If you are using them in series probably best to charge them in series. Make sure that they both of your batteries are the same capacity and at the same state of charge prior to starting. LifePo4 or SLA? You might want to look at something like the battery balancer that watts247 offers. I found inbalance overall to be a limitation in building larger lithium batteries with 280ah cells by breaking them into 12V versions with individual BMS to be moveable and still use them in a 48V series configuration. Once one battery hits full charge it shuts down the whole charging system. The balancer will act as a shunt to balance and charge the series battery bank as a whole if they become imbalanced.
The growatt will be charging the 24 volt battery bank via solar or shore power. I’m not worried about that battery bank. It’s the 12 volt batteries that will be powering the 12 volt lights/landing gear/slides…. I’m looking at the most efficient way to keep these 12 volt batteries charged.
 
In typical fashion for me I’ll ask the question: is there any reason why you can’t run a single 12V deep cycle and a 100W panel with pwm like https://www.amazon.com/dp/B00JML23X0/ref=cm_sw_r_cp_api_glt_fabc_E99XDCJP80VR6MPP2HX3 and keep that for non-inverted loads like the jack? (Price though- I paid $185 for this brand with two 100W panels 3-4 years ago!)

Then you have the best of two worlds and redundancies for lights. Separate the converter charge for that circuit with a switch? I’m guessing you are more than smart enough to get that going lol

Had you considered this? Especially since you probably have an RV lead acid now? With light responsible use and monthly acid level check the lead acid battery could go for 5 or more years. That WindyNation pwm did very well for me; it is clonie looking but from others that look like it I suspect it is a grade above or different- menus are great.
Haven’t thought of that. I like that idea.
 
Thanks for the reply. Im looking to use a growatt all in one inverter. To my knowledge they do not make one for 12 volts, hence the reason for a 24 volt battery bank.
I’ve looked at the step down converter. I would need to use multiple ones to achieve the 250 amps the landing gear can draw. I’ve seen some people have used the step down converter for the lights inside the rig and kept a separate battery for slides and landing gear.
Continue to have the one 12v battery to power all the high load stuff (like landing gear etc) that is short duration. Just use a standard 12v charger to keep it topped off.
 
Continue to have the one 12v battery to power all the high load stuff (like landing gear etc) that is short duration. Just use a standard 12v charger to keep it topped off.
he will still have other ‘house’ 12V stuff
 
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