diy solar

diy solar

Charge wire in 7-way trailer plug and lithium battery

HRTKD said:
For the breakaway system, I don't think there is a direct connection - without a governor - between the battery and the brakes.
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It is a direct connection if installed properly to CFR DOT requirements. You can test it on your trailer - pull the breakaway pin and wait :cool: . If wiring is robust enough -only the battery will need recharging. You will hear a humming sound from each magnet(brake) No different for EOH - breakaway event triggers continuous pump run until something fails or is manually reset.
 
@mapguy525 , still not convinced that in a breakaway event, the engaged brake would draw a surged 1C (100A) or more and damage a LifePo4 battery - I have a 16' single axle trailer and per resource I can find on the web it draws about 6amp or so. I expect it to continue to draw that much power to stay engaged even in a breakaway event. It doesn't make sense that the brake would surge to 100A from 6A just because it stay engaged. the power a brake draws at any given moment should be a function of how hard you step on brake, not a function of how long it stay engaged. Since this safety related, If you have any links, that explain this behavior it would be super helpful.
 
The RV Tech I know confirmed the blog blurb that I included in post #20. The breakaway system isn't going to suck 1C out of 100 Ah battery. It's only going to pull as many amps as it normally would, about 3 amps per brake.
 
HRTKD said:
The RV Tech I know confirmed the blog blurb that I included in post #20. The breakaway system isn't going to suck 1C out of 100 Ah battery. It's only going to pull as many amps as it normally would, about 3 amps per brake.
Click to expand...

Ok. Don' t agree. But it is all good.
 
Of course if your trailer breaks away and then brakes away it probably won't matter what happens to the battery or brakes and wiring ;)
(unless it causes it to catch fire thereby adding insult to injury)

I will be in the midst of wiring one of these up on a trailer soon (my first), good info here.

Thanks!
 
mapguy525 said:
It is a direct connection if installed properly to CFR DOT requirements. You can test it on your trailer - pull the breakaway pin and wait :cool: . If wiring is robust enough -only the battery will need recharging. You will hear a humming sound from each magnet(brake) No different for EOH - breakaway event triggers continuous pump run until something fails or is manually reset.
Click to expand...

I agree with this. I wire trailers often. The breakaway switch on a trailer is just a switch....no further intelligence. When you pull the switch, it directly connects the batteries to the brakes. When designed correctly, it should be unfused as this is an emergency circuit.

I'll do some testing on my smaller trailer with 8" drums and see what kind of amperage readings I can get on lead acid and lithium so we can put this to bed. Trailer brakes are just electromagnets so i'm not expecting them to operate differently with two slightly different power sources.
 
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CascadeOffGrid said:
I agree with this. I wire trailers often. The breakaway switch on a trailer is just a switch....no further intelligence. When you pull the switch, it directly connects the batteries to the brakes. When designed correctly, it should be unfused as this is an emergency circuit.

I'll do some testing on my smaller trailer with 8" drums and see what kind of amperage readings I can get on lead acid and lithium so we can put this to bed. Trailer brakes are just electromagnets so i'm not expecting them to operate differently with two slightly different power sources.
Click to expand...

I look forward to the results.
 
This was provided by RV_Tech over on the Ford-Trucks.com forum:

Testing your own system is very simple to do. First of all make sure your trailer battery is fully charged or there abouts i.e. no dead battery tests. Then leaving your seven pin unpinned from your tow vehicle take your clamp meter and put it around either one of the two wires on your break-away switch. Pull the pin and have someone try to pull your camper while you watch your meter. Your driver should feel a great deal or resistance and your meter will show you the amp draw of your magnets. Your meter should be reading close to 12; it could be somewhat more or less, but close. If you meter reading is good, but your trailer braking is poor, adjust your trailer brakes. If the meter reading is too low, focus on the wiring, magnets, etc. Don't forget to put the pin back in the break-away where you are done. In the end, all we really care about is how well our own systems are functioning.
Click to expand...
 
Well sorry for the LONG delay. I finally got around to doing this testing. I tested this on two separate trailers yesterday. One of this trailers is a single axle that I built with brakes and the other was a 23' camper trailer that I was converting to lithium.

Both trailer brake systems worked fine on the lithium batteries. For the test, the trailers were NOT hooked up to a tow vehicle. I pulled the breakaway pin and measured amperage with a Fluke meter with a DC clamp.

Single Axle Trailer
12V Sealed Lead Acid - 6.8 amps
12V Battleborn 100aH Only - 7.0 amps

Tandem Axle Travel Trailer
12V Flooded Factory Batteries - 12.8 amps
12V Battleborn 100aH Battery Only - 13.1 amps
 
CascadeOffGrid said:
Well sorry for the LONG delay. I finally got around to doing this testing. I tested this on two separate trailers yesterday. One of this trailers is a single axle that I built with brakes and the other was a 23' camper trailer that I was converting to lithium.

Both trailer brake systems worked fine on the lithium batteries. For the test, the trailers were NOT hooked up to a tow vehicle. I pulled the breakaway pin and measured amperage with a Fluke meter with a DC clamp.

Single Axle Trailer
12V Sealed Lead Acid - 6.8 amps
12V Battleborn 100aH Only - 7.0 amps

Tandem Axle Travel Trailer
12V Flooded Factory Batteries - 12.8 amps
12V Battleborn 100aH Battery Only - 13.1 amps
Click to expand...

How long did you leave each of the tests running? IE length of time magnets were fully engaged.
 
this is what the break away batteries look like.

71f6chZ6ehL._AC_UY218_.jpg
They are like 3x3x5 They are not exactly a high current battery

Trailer brake wiring is at best 12ga I don't expect them to draw more than 15a continuous.

As it was a topic of discussion in the thread, the onboard controler sends a varable voltage to the electric brakes. The "gain" control on the controler will up the top voltage (full bars) that the controller will output. Max gain gets you to max 14.4 volts.

This is also used to control the amount of brakeing force needed on the trailer. Empty my 10K equipment trailer will lock up brakes at about 6 (i run it at 5). When I have my tractor or skidsteer on it, I run it at 10.
 
CascadeOffGrid said:
Well sorry for the LONG delay. I finally got around to doing this testing. I tested this on two separate trailers yesterday. One of this trailers is a single axle that I built with brakes and the other was a 23' camper trailer that I was converting to lithium.

Both trailer brake systems worked fine on the lithium batteries. For the test, the trailers were NOT hooked up to a tow vehicle. I pulled the breakaway pin and measured amperage with a Fluke meter with a DC clamp.

Single Axle Trailer
12V Sealed Lead Acid - 6.8 amps
12V Battleborn 100aH Only - 7.0 amps

Tandem Axle Travel Trailer
12V Flooded Factory Batteries - 12.8 amps
12V Battleborn 100aH Battery Only - 13.1 amps
Click to expand...

Thanks for running this test and posting results. It's good to know that the breakaway system isn't going to suck all possible amps out of a LiFePO4 battery.
 
CascadeOffGrid said:
I'd estimate about 10-15 seconds. Amperage was holding steady.
Click to expand...
Thanks for that data point.

My concern would be worn, but still serviceable magnets being subjected to +5 minutes of inadvertent emergency brake application.

schmism said:
Trailer brake wiring is at best 12ga I don't expect them to draw more than 15a continuous.
Click to expand...
Like all things DC - wire sizing is based on the round trip distance and the amperage/voltage carried. For a Trailer that is a 30' distance from 7 way connector to last axle - the wiring shout be 10 gauge to have > 2% voltage drop. This comes directly from the Dexter Axle service manual resources. Think about the long run of miniscule wiring on the average trailer. Most RV's have barely minimal wiring gauge plus bad splices.
 
mapguy525 said:
My concern would be worn, but still serviceable magnets being subjected to +5 minutes of inadvertent emergency brake application.
Click to expand...

Should your breakaway system have to activate, the last thing you're going to care about are the magnets. Cleaning your pants will probably rank a bit higher. :)
 
You are missing the point entirely. Yes, my concern is an outlier. But it is a regularly occurring outlier.

No concern about normal or actual emergency event operation.

Great concern over the inadvertent activation of the breakaway system. IE parked in the campground and the breakaway pin is pulled. Nobody notices or is around. This happens all the time.
 
mapguy525 said:
Great concern over the inadvertent activation of the breakaway system. IE parked in the campground and the breakaway pin is pulled. Nobody notices or is around. This happens all the time.
Click to expand...

I have never heard of that happening. When my trailer is parked, the breakaway cable is tucked up into the tongue to prevent anyone from stepping on it.

I'll grant you that inadvertent activation would drain the battery and could burn out the magnets.

If I was going to prank someone at the campground, pulling their breakaway cable isn't something I would do. Turn off their propane, drain their fresh water tank, open the black water valve without opening the pipe cap (then close the valve so they don't know what's going to hit them), loosen their stabilizer jacks, close the railing on the door, etc. If inadvertent activation is a prevalent as you say, I would expect the system to have an audible warning.
 
You won’t damage anything. Most modern cars alternators charge up to 14-14.4v then drop down to 14ish while driving. You probably have 20’ of #12wire running to the back of your tow vehicle, that’s a lot of resistance. Let’s say your cars battery is at 13v, and your trailer lifepo4 battery is at 14v, your have very low current back feeding the car, probably under 1amp.

I’ve tested this hands on in several conditions. Even a dead lifepo4 (11v) is only able to pull about 10amps from the vehicles charging system. There is just too much resistance. The factory installed 7pin charge circuitry is designed to trickle charge one of those 10ahr trailer brake batteries that is commonly mounted to the side of the trailers tongue.
 
mapguy525 said:
Thanks for that data point.
My concern would be worn, but still serviceable magnets being subjected to +5 minutes of inadvertent emergency brake application.


Like all things DC - wire sizing is based on the round trip distance and the amperage/voltage carried. For a Trailer that is a 30' distance from 7 way connector to last axle - the wiring shout be 10 gauge to have > 2% voltage drop. This comes directly from the Dexter Axle service manual resources. Think about the long run of iscule wiring on the average trailer. Most RV's have barely minimal wiring gauge plus bad splices.
Click to expand...

DOT regs say the battery has to be big enough to hold the brakes for 15 mins after breakaway is activated.


I think this is being way over thought. trailers have been wired this way for years without issue.

Also as test proved they cannot pull any more current than the magnets are designed for. Simple ohms law.

Greg
 
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