6 ----> 24 volts

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Desert_Rat

Guest
Anyone see any issues with this first (test) bank?

1) Double crimped
2) Dialectric grease applied
3) 2 AWG cable. I wanted 2/0 but ordered incorrectly. Based on what I've read, it's fine. Bank will be < 5' from MPPT and Inverter

edit: Couple of questions I have are:
1) I'm surprised + is on the negative lead, and visa versa. I guess I should attach the black cable to the + terminal?
2) How much of a gap between batteries should I have when I move them to the box? I'll have 1 24v fan and a vent, both about 3-4" squared.
 

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Desert_Rat

Guest
Funny, I saw a reference to that an hour ago and was all.... what tha...?

Is that really legit?
 

SeilerBird

Well-known member
Joined
Feb 25, 2012
Posts
15,691
Location
St Cloud Florida USA
Desert_Rat said:
Funny, I saw a reference to that an hour ago and was all.... what tha...?

Is that really legit?
I am sorry, that is wrong. It only gives you 12 volts and you wanted 24. What do you want 24 volts for?
 
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Desert_Rat

Guest
One MPPT for over 2kw of PV. Pretty much mandatory, and on the low side - I'll still need a 100A MPPT.
 

HueyPilotVN

Well-known member
Joined
Jun 5, 2012
Posts
2,277
The series wiring of the four 6 volt batteries will give you 24 volts.

I am still however not sure that I understand why you want to make your system in a non standard (for RVs) voltage.

There is an advantage in that 24 volt systems might use smaller cables than a 12 volt system just as 110 volt systems also do not need large conductors.

The biggest disadvantage is that you are going to need to convert much of your electrical system back to 12 volts either at the battery bank or multiple times at the loads.

You are also going to have to take this into consideration with every component that you buy or convert to 12 volts.

I am just throwing this out there since you are mostly still in the planning stage.

Good Luck with whatever you do and keep us in the loop so that we can learn from your experience with this different approach.

As a side comment my company does use 24 volt power in our Mobile Hospital Units for certain dedicated uses.  The electric servo motors for the hydraulics in the huge slideouts are 24 volt systems but these are stand alone closed systems and the standard for other DC uses in these unit is 12 volts.
 

AStravelers

Well-known member
Joined
Nov 14, 2016
Posts
1,591
Location
San Antonio, TX
Desert_Rat said:
Anyone see any issues with this first (test) bank?

1) Double crimped
2) Dialectric grease applied
3) 2 AWG cable. I wanted 2/0 but ordered incorrectly. Based on what I've read, it's fine. Bank will be < 5' from MPPT and Inverter

edit: Couple of questions I have are:
1) I'm surprised + is on the negative lead, and visa versa. I guess I should attach the black cable to the + terminal?
2) How much of a gap between batteries should I have when I move them to the box? I'll have 1 24v fan and a vent, both about 3-4" squared.
I don't see anything wrong with the way the batteries are wired for a 24V system.  So don't understand you question #1.

I don't know that you need a gap between the batteries, but they should be tied or clamped down.

These are flooded cell batteries so you need good ventilation.  Using a fan I would push air into the compartment.  I am not sure if an exhaust fan could ignite the hydrogen gas given off by the batteries. 

The wire size depends on how much current you push though the wire.  Assuming you used a wire size calculator and accounted for 10' of wire and not the one way distance of 5' then you should be OK. 
 

HueyPilotVN

Well-known member
Joined
Jun 5, 2012
Posts
2,277
Desert_Rat said:
One MPPT for over 2kw of PV. Pretty much mandatory, and on the low side - I'll still need a 100A MPPT.

As I reread your post it may be that your choice of 24 volts may be mostly driven by your plans for the way you intend to handle the "Solar Charging" side of the system.

Most Solar Power systems in RVs take advantage of the fact that there may well be several sources of recharging your batteries.  These input sources include a convertor/charger, possibly an Invertor/Charger, the Alternator from the vehicles engine, as well as the fact that you can have multiple charge lines from different Solar Charge Controllers.

If in fact you are committed to using a single very large charge controller, then you will need large heavy cables to carry the amperage to the batteries.  However this is not the only way to get lots of electrical charge back into your batteries.  You can use multiple charge controllers, (all with smaller cables feeding into a common point).

This will allow you to leave all of your 12 volt system intact.

I have also mentioned in other posts that another alternative is using more than one dedicated battery bank and splitting the loads and the charging sources.
This option would also reduce the weight as opposed to mounting one large battery bank on your trailer tongue.

Just trying to help with alternate suggestions.
 

Ernie n Tara

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Joined
May 16, 2009
Posts
4,063
Location
Ft Myers, FL
I'd reconsider the 24 V issue. There are two reasons for that; first conversion back from 24 to 12 V is going to be perhaps 90% efficient so you're giving away 200 W of that hard earned power when you use your standard appliances. Second, 24 V equipment is usually much more expensive, if you elect not to down convert, since it is less used and usually designed for commercial applications.

I can't believe it won't be more eficient and less costly to just use larger cables (or more of them).

Ernie
 
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Desert_Rat

Guest
AStravelers said:
I don't see anything wrong with the way the batteries are wired for a 24V system.  So don't understand you question #1.

If you notice, the red lead (standard + lead)  is tied to the + terminal, but my voltmeter is connected in reverse to get its positive reading. I'm just curious why the positive charge is at the negative terminal on the bank instead of at its positive terminal. It's obviously inherent to a series connect but I found it odd is all.
 
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Desert_Rat

Guest
Y'all may not believe it, but if I chose to share this project on a board centrally dedicated to solar, this 12v curiosity would be about 48v instead. 'You can't use 24v, that's just wrong!' 'I would highly recommend you move to 36 or 48v instead'

Yup

Understand that I've been researching this project for a good while, and while my conclusions may not be perfect, they are conclusions I'm determined to run with. I understand the advantages and disadvantages of 12, 24, 48v. Each has been thoroughly weighed, and my reasoning to go 24v has been addressed here for all to see. This is not a 400 watt project that would be more suitable at 12v, it's gonna be over 2kW and you simply cannot competently manage that at 12v, or you shouldn't have to anyway.

The reason I'm sharing is because I'm a novice with all skills necessary to build the system properly, so I'm seeking more informed guidance along the way. Like I said on my battery box post, 'I'm not a carpenter or metal worker, but I think it came out ok'. But did it? Will 1.5" pine be able to withstand 720lb of batteries... on the road no less? How about tongue weight (that was covered). Was my 2 AWG fitting crimped properly? Are the different cable lengths used considered ok?

Thank you for any and all input.
 
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markbarendt

Guest
Desert_Rat said:
If you notice, the red lead (standard + lead)  is tied to the + terminal, but my voltmeter is connected in reverse to get its positive reading. I'm just curious why the positive charge is at the negative terminal on the bank instead of at its positive terminal. It's obviously inherent to a series connect but I found it odd is all.

The black lead should be plugged into the "common" on the meter. Once you correct the plug positions it will read correctly.
 
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Desert_Rat

Guest
Look at the voltmeter, it's reading correctly as is - backwards

Must be inherent to a series connect. positive charge on - terminal, negative charge on + terminal.
 
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markbarendt

Guest
Desert_Rat said:
If you notice, the red lead (standard + lead)  is tied to the + terminal, but my voltmeter is connected in reverse to get its positive reading. I'm just curious why the positive charge is at the negative terminal on the bank instead of at its positive terminal. It's obviously inherent to a series connect but I found it odd is all.
Second point. No.

When working with electricity and meters it is important that you understand what to expect.

Finding it odd was the correct response to the reading you got.

When you get an unexpected reading like that asking why is the next step, you did well asking here.

Never assume odd results are inherent, they almost never are.

 
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markbarendt

Guest
Desert_Rat said:
Look at the voltmeter, it's reading correctly as is - backwards

Must be inherent to a series connect. positive charge on - terminal, negative charge on + terminal.
No

Swap the wires on your meter.

Black to "Com" Red to V
 
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Desert_Rat

Guest
What tha... didn't notice that. I'm blaming it on the dog. yeah, that's it!
 
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markbarendt

Guest
Can't tell what the dog breed is exactly from your avatar but both Ausies and Border Collies are too smart to get that wrong.
 
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