wa8yxm wrote:
Measure the current (I's use a clamp on ammeter first to make sure as most in-lines are limited to around 10 amps.
Then look at the wire size.. And length.
Then google Wire Size Calculator
:R
Good grief!
Reading the current will tell the OP zero, zilch, zero on WHERE the problem is.
OP already knows that they are not getting full voltage at the magnets, therefore they will never get full current draw by the magnets. OP already knows they are not getting full braking effort.
Now if you were wanting to check the "balance" of current being drawn between each magnet to make sure the magnets are evenly getting the same voltage then a current reading of each magnet will tell you quickly if it is balanced without the need to access the wires electrically.
This isn't "rocket science", it is Elementary level basic electronics.
As far as using wire size calculators, they are designed for high voltage applications like 120V/240V and are designed around the acceptable NEC voltage drops for 120/240 which is 3% or 5% depending on application.
5% loss at 120V is 6V and you would get 114V which is acceptable
5% of loss at 12.8V is huge at .64V meaning you only get 12.16V when your battery voltage range is 10.5V (dead) to 12.8V fully charge resting voltage.
No need to "look up" the wire gauges, Dexter has already done that work for you in their manual I linked above. In that manual they give the MINIMUM recommended wire gauge for the length of the RV and the quantity of wheels.
Using Dexters charts, most average length RVs with 4 wheels will fall into 14 ga, 12 ga or 10 ga wire as the absolute minimum wire size. Extremely long RVs with 6 wheels fall into 10 ga or 8 ga wire.
I highly doubt most RV manufacturers will pop for more than 14Ga wire.. Myself I have found 16 ga wire used on my TTs and my 18ft 10K flatbed trailer they used 12 ga wire (unlike the cheap RV manufacturers).
Once again, OP already knows they are not getting full BATTERY VOLTAGE AT THE MAGNETS. That means there is a high resistance somewhere BEFORE the axles.