24 VDC and 12 VDC brakes in Fifth Wheel

[chrisski]

I’ll take a look at this calculator when I get home.

What I have now to put this battery box and inverter together on top of the batteries I mentioned is an ANL 300 amp inline fuse to hook next to the battery, and the battery cabling is 2/0 welding cable, and there‘s potential to have the inverter with 4’ positive cable, and 4’ negative cable, but more likely 2’ feet away. Whatever wiring I use to go from the battery to the inverter will likely be purchased from Home Depot, so THHN I think.

 

[John Frum]

I’ll take a look at this calculator when I get home.

What I have now to put this battery box and inverter together on top of the batteries I mentioned is an ANL 300 amp inline fuse to hook next to the battery, and the battery cabling is 2/0 welding cable, and there‘s potential to have the inverter with 4’ positive cable, and 4’ negative cable, but more likely 2’ feet away. Whatever wiring I use to go from the battery to the inverter will likely be purchased from Home Depot, so THHN I think.

Thhn != Welding cable.

 

[chrisski]

I’m admittedly new to the wiring, but the 2/0 welding cable I have to attach the batterues is really flexible, and the 2/0 I get locally is quite stiff and takes some effort to bend. I’ll see exactly what cable it is when I get home.

I was an electronics techician a while ago, but never dealt with thick wiring. Also, our tool kits were provided for us and had all the tools we needed in them, and doing this on my own, I was surprised to see what it takes to tool up.

 

[piciu1982]

I have similar setup right now, 24V, I do not use 12V dc/dc inverter for electric brakes, you can buy small 12V battery (they have whole setup at etrailer.com with small battery box, charge indicator etc) and connect it only to 7 pin round connector , its getting charged from truck , and its used only to power break away switch anyway

 

[chrisski]

I have similar setup right now, 24V, I do not use 12V dc/dc inverter for electric brakes, you can buy small 12V battery (they have whole setup at etrailer.com with small battery box, charge indicator etc) and connect it only to 7 pin round connector , its getting charged from truck , and its used only to power break away switch anyway

So, the only thing the 7 pin powers is the battery? The way I see that working is all 12 volts except the battery comes from the 24 to 12 VDC converter except the breaks, which are powered by that battery.

Also, do you remove this small battery and store it if the trailer is not used for a while?

 

[piciu1982]

google 7 pin trailer connector pinout, one of the pins is aux power, its on when ignition is on, its to charge anything 12v on the trailer, only thing that needs to be charged is 12 v small battery, battery powers brake away switch, witch is not in use until u pull emergency break away switch thats connected to your hitch, nothing else, u dont have to charge it from trailer side, when its charged it stays like that for a long time, brake signal comes from trucks brake controller on different pin, goes straight to your brakes, its separate from everything else

 

[chrisski]

For a high frequency inverter.
ac continous watts * 1.15 conversion factor / low voltage cutoff = dc amps
dc amps * 1.5 fuse headroom = fuse amps
now plug dc amps and wire length and system voltage into this calculator.
Please post the resulting wire gage and fuse size so that I know you are engaged.

219 DC AMPS
328 Fuse Amps

For 10 feet of wire, worst case 5' each way from battery:

2/0--1.46%
1/0--1.84%
1--2.33%

Not sure of the math for "How long will the 478 AH battery bank last discharching 219 amps" is done but another reference I got says that Peukert's law says my 478 amp hour battery bank should only discharge 143 amps if drained in one hour. I don't know exactly how to determine the Pukert Constant of a Trojan battery. Its not in the owners manual and I can't find anything about a max discharge rate. I did a one amp calculation and came up with it will last for 274 hours at one amp. Not quite what I'm trying to do though.

google 7 pin trailer connector pinout, one of the pins is aux power, its on when ignition is on, its to charge anything 12v on the trailer, only thing that needs to be charged is 12 v small battery, battery powers brake away switch, witch is not in use until u pull emergency break away switch thats connected to your hitch, nothing else, u dont have to charge it from trailer side, when its charged it stays like that for a long time, brake signal comes from trucks brake controller on different pin, goes straight to your brakes, its separate from everything else

That's an idea do you do this?

 

[John Frum]

219 DC AMPS
328 Fuse Amps

For 10 feet of wire, worst case 5' each way from battery:

2/0--1.46%
1/0--1.84%
1--2.33%

Not sure of the math for "How long will the 478 AH battery bank last discharching 219 amps" is done but another reference I got says that Peukert's law says my 478 amp hour battery bank should only discharge 143 amps if drained in one hour. I don't know exactly how to determine the Pukert Constant of a Trojan battery. Its not in the owners manual and I can't find anything about a max discharge rate. I did a one amp calculation and came up with it will last for 274 hours at one amp. Not quite what I'm trying to do though.



That's an idea do you do this?

Ok so 2/0 wire so that your fuse protects the wire and not the other way around.
What voltage is you use for low cutoff?

 

[chrisski]

Ok so 2/0 wire so that your fuse protects the wire and not the other way around.
What voltage is you use for low cutoff?

I used 10.5. The manual said 10.5 ± .3

 

[John Frum]

I used 10.5. The manual said 10.5 ± .3

You should only discharge your lead acid batteries to 50% for longevity.

 

[chrisski]

You should only discharge your lead acid batteries to 50% for longevity.

I've got a battery monitor to install to keep me above that.

Ultimately, what I'd like to do is run an 1700 watt electric kettle with 1.7 liters of water in it, that takes seven minutes to boil, and do this four times a day. Since the only benchmark I have is the one hour rate is 178 amps, math in my head tells me that running the electric kettle twice may get me pretty close to the 50% mark. If that's the case, I think I'd need a much bigger battery bank to use the electric kettle.

 

[piciu1982]

219 DC AMPS
328 Fuse Amps

For 10 feet of wire, worst case 5' each way from battery:

2/0--1.46%
1/0--1.84%
1--2.33%

Not sure of the math for "How long will the 478 AH battery bank last discharching 219 amps" is done but another reference I got says that Peukert's law says my 478 amp hour battery bank should only discharge 143 amps if drained in one hour. I don't know exactly how to determine the Pukert Constant of a Trojan battery. Its not in the owners manual and I can't find anything about a max discharge rate. I did a one amp calculation and came up with it will last for 274 hours at one amp. Not quite what I'm trying to do though.



That's an idea do you do this?

Thats how all trailers r wired, beside res and travel trailers that have shore power inverter that also charge the same battery

 

[piciu1982]

https://www.etrailer.com/Trailer-Breakaway-Kit/Bright-Way/3802339.html?feed=npn&gclid=Cj0KCQjw-O35BRDVARIsAJU5mQXoVs6CPvNDwAyEkgFHDmewV8-nR6a0iua4vyhdk8szXjBIuqJGsCwaAmUCEALw_wcB

 

[bpal]

I've got a battery monitor to install to keep me above that.

Ultimately, what I'd like to do is run an 1700 watt electric kettle with 1.7 liters of water in it, that takes seven minutes to boil, and do this four times a day. Since the only benchmark I have is the one hour rate is 178 amps, math in my head tells me that running the electric kettle twice may get me pretty close to the 50% mark. If that's the case, I think I'd need a much bigger battery bank to use the electric kettle.

not factoring for inverter and other inefficiencies:

1700w / 12v = 141a
141a / 2 = 71ah used in 30 minutes of kettle

71ah is 15% of your 478ah

 

[chrisski]

not factoring for inverter and other inefficiencies:

1700w / 12v = 141a
141a / 2 = 71ah used in 30 minutes of kettle

71ah is 15% of your 478ah

Now that you point out I am using 141 amps for this kettle I feel better about large sized inverter wiring and using this kettle. Because of the quicker discharge rates under higher amperages, running the kettle for 30 minutes comes out to discharging the battery close to 50%. Since this is likely to be done when the sun is up, the full 141 amps is not likely come from the battery pack, so I'm thinking 30 minutes of usage may drain the battery to around 35%-30%.

I guess what I'm getting at is the that is 71 AH used at the C20 rate of 478, but because of the higher amperages the theoretical C1 rate is 143. (One hour max discharge rate of the battery is 143). If a battery is discharged in an hour, thus table says to multiply the C20 rate by .3 to get the amps available to discharge.

This is a table I was given to calculate C rates:

	Battery Pack Amp Hour	478​
Discharge Rate Coefficient
1 Hour	0.3​	143.4​
2 Hour	0.5​	239​
3 hour	0.6​	286.8​
4 hour	0.65​	310.7​
5 hour	0.7​	334.6​
6 hour	0.75​	358.5​
8 hour	0.8​	382.4​
10 hour	0.85​	406.3​
12 hour	0.9​	430.2​
16 hour	0.95​	454.1​
20 hour	1​	478​
24 hour	1.05​	501.9​
36 hour	1.1​	525.8​
72 hour	1.25​	597.5​
100 hour	1.3​	621.4​

https://www.solarpaneltalk.com/foru...y-storage/11731-peukert-law-batteries-and-you

The table is supposed to be used to plan only and the battery manufacturer will publish more accurate data then this table. My battery manufacturer tech sheet does not go down to C20, but does publish a C10 rate that would be 422 AH, and this table says 382, so the potential is there for my batteries to be better than the table,

 

[John Frum]

Now that you point out I am using 141 amps for this kettle I feel better about large sized inverter wiring and using this kettle. Because of the quicker discharge rates under higher amperages, running the kettle for 30 minutes comes out to discharging the battery close to 50%. Since this is likely to be done when the sun is up, the full 141 amps is not likely come from the battery pack, so I'm thinking 30 minutes of usage may drain the battery to around 35%-30%.

I guess what I'm getting at is the that is 71 AH used at the C20 rate of 478, but because of the higher amperages the theoretical C1 rate is 143. (One hour max discharge rate of the battery is 143). If a battery is discharged in an hour, thus table says to multiply the C20 rate by .3 to get the amps available to discharge.

This is a table I was given to calculate C rates:

	Battery Pack Amp Hour	478​
Discharge Rate Coefficient
1 Hour	0.3​	143.4​
2 Hour	0.5​	239​
3 hour	0.6​	286.8​
4 hour	0.65​	310.7​
5 hour	0.7​	334.6​
6 hour	0.75​	358.5​
8 hour	0.8​	382.4​
10 hour	0.85​	406.3​
12 hour	0.9​	430.2​
16 hour	0.95​	454.1​
20 hour	1​	478​
24 hour	1.05​	501.9​
36 hour	1.1​	525.8​
72 hour	1.25​	597.5​
100 hour	1.3​	621.4​

https://www.solarpaneltalk.com/foru...y-storage/11731-peukert-law-batteries-and-you

The table is supposed to be used to plan only and the battery manufacturer will publish more accurate data then this table. My battery manufacturer tech sheet does not go down to C20, but does publish a C10 rate that would be 422 AH, and this table says 382, so the potential is there for my batteries to be better than the table,

Whatever comes out of your battery has to go back in.
Its just a buffer.

 

[chrisski]

Whatever comes out of your battery has to go back in.
Its just a buffer.

Yes. Using that electric kettle 4 times would cost me almost 4 hours of perfect charging conditions if the quick amperage drain really does take half the battery life out of it.

Thats how all trailers r wired, beside res and travel trailers that have shore power inverter that also charge the same battery

I guess I'm reluctant to charge the battery solely off the 12 Volt trailer hitch like you mentioned because the couple of times I drove without a fully charged trailer battery, the 12 volt accessory did not charge the battery which left me without breaks.

If I did go to 24 VDC and were boondocking, there'd be no option to plug in to shore power to charge the 12 VDC side off the converter. I can't find a commercial off the shelf 24 VDC to 12 VDC charger, there's plenty of converters that simply make 12 volts all DC items in my trailer needs except the battery--these converters don't supply a charging algorithm. I've found one or two 24 VDC to 12 VDC converter chargers, but these have inputs of no more than 24 VDC, and the manuals say not to exceed 24 VDC.

 

[John Frum]

Yes. Using that electric kettle 4 times would cost me almost 4 hours of perfect charging conditions if the quick amperage drain really does take half the battery life out of it.

It takes 5 minutes for my 1.7 litre kettle to boil.
Thats ~500 watt hours.

 

[bpal]

maybe a nice Yeti thermos could cut down on your usage

 

[chrisski]

It takes 5 minutes for my 1.7 litre kettle to boil.
Thats ~500 watt hours.

So, when you run your electric kettle on solar power, do you have a battery monitor that will watch how quick the battery % goes down?

I guess what is getting me is watt hours is one measurement and should work well for things close to a C20 draw, but for my 478 Amp Hour System at the C20 rate, once I draw amps much quicker than 24 amps per hour, like the 141 amps per hour rate, the math I’m doing says that when I run my kettle for 5 minutes, that will cost me 8% of my battery power If the C1 rate of the battery is 143 amps. Between some of this amperage coming from the panels in the daytime (in my favor), and system losses (not in my favor), this 8% should at least be a ball part number.

maybe a nice Yeti thermos could cut down on your usage

I was convinced before I came to this forum that going with a 2000 watt inverter was a bad and dangerous idea on a 12 VDC system. I’m trying to use some math to see with proper sized wires like 2/0 and flooded lead acid batteries, this could be done.

If we got a 2000 watt inverter, the other people in my family would appreciate The switch to solar, but with a 1000 watt inverter, they’d miss some things. My idea of camping is a little more rustic than there’s.