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LK23 · 02-10-2023, 04:55 PM

I am installing the Demco Towed Vehicle Battery Charge Wire on my tow vehicle. After connecting the wire to my bumper 7-wire receptacle I tested the continuity from the receptacle to the end of the charge wire—No connectivity. This charge wire has a diode.

My question: Should I have connectivity through the diode? If not, how do I test the wiring?

Ranger Smith · 02-10-2023, 04:59 PM

Depending on what meter lead goes where .One way will show open and the other way there will be some resistance but all is OK because you are reading through the diode.

LK23 · 02-10-2023, 05:12 PM

I attached one end of my Fluke multimeter to the center 7-wire receptacle at the bumper and the other end at the charge wire fuse holder just past the diode. I have the Fluke meter was set to ohms and the meter showed nothing—telling me there was no connectivity.

I tested from the receptacle to the input side of the diode and had connectivity.

Ranger Smith · 02-10-2023, 06:16 PM

Reverse the leads. A diode is a one way device and will show an open circuit one way

THenne1713 · 02-10-2023, 10:42 PM

A diode will generally have a LOW value with one polarity, and VERY HIGH value with reverse polarity.

Isaac-1 · 02-11-2023, 03:28 AM

As mentioned reverse the leads, also put the fluke meter in ohms mode, not continuity mode to get a detailed resistance reading.

LK23 · 02-11-2023, 02:47 PM

Thanks for all the helpful replies. Today I tried it again while reversing the Fluke probes.

With the positive probe on the output side of the diode my Fluke showed no reading. With the negative probe on the output side of the diode my Fluke registered 5850 ohms, confirming the diode is working properly and the charging wire should keep my toad battery charged as designed. See photos.

swduns · 02-11-2023, 05:40 PM

I had my toad wired bu etrailer. They used the power pin in the 7 pin & a charging module to the toad battery. On a long trip the toad battery died. I had to run a large separate direct wire to charge the toad battery. Point - using the 7 pin power wire maybe inadequate depending on motorhome wire size and toad power consumption

eyecando · 02-11-2023, 05:53 PM

Quote:

Originally Posted by LK23

I am installing the Demco Towed Vehicle Battery Charge Wire on my tow vehicle. After connecting the wire to my bumper 7-wire receptacle I tested the continuity from the receptacle to the end of the charge wire—No connectivity. This charge wire has a diode.

My question: Should I have connectivity through the diode? If not, how do I test the wiring?

That depends on the meter you are using and the polarity of your connections. Some multimeters don't have a high enough output voltage to turn on the diode and it will always read open. It will always read open if you reverse bias the diode by applying the meter positive wire to the cathode and the negative wire to the anode. Try reversing your connections and or using a different ohm range.

Put your red wire on the anode side and the negative wire on the cathode side of the wire to test continuity.

Be aware that a diode in the circuit will reduce the voltage applied to the towed vehicle by about 0.7 volts which along with the voltage drop in the wiring may cause issues with properly charging the battery.

If the meter has a diode test function, use that setting to test continuity.

You could also apply voltage to the vehicle end and verify you see voltage at the trailer plug to verify the continuity somewhat.

THenne1713 · 02-11-2023, 11:22 PM

I hope your large, separate CHARGE wire is fused ON BOTH ENDS, and relay controlled

Argosy · 02-15-2023, 05:46 AM

Why would it need a relay?

dssl · 02-16-2023, 12:22 PM

The way I confirmed my toad charger was working was by comparing toad battery voltage before and after I connected it and started up the coach.

THenne1713 · 02-17-2023, 01:16 AM

Sounds like The purpose of diode is to prevent coach/ TOW chassis accessories from draining TOAD Battery? (I.e Charge can ONLY flow INTO TOAD) The purpose of the IGN controlled RELAY is to disconnect/ Prevent TOAD from draining CHASSIS BATTERY and leaving you stranded and unable to start the TOW Vehicle; i.e. IGN=OFF= Charge connection= OFF.

eyecando · 02-18-2023, 09:26 AM

Quote:

Originally Posted by THenne1713

Sounds like The purpose of diode is to prevent coach/ TOW chassis accessories from draining TOAD Battery? (I.e Charge can ONLY flow INTO TOAD) The purpose of the IGN controlled RELAY is to disconnect/ Prevent TOAD from draining CHASSIS BATTERY and leaving you stranded and unable to start the TOW Vehicle; i.e. IGN=OFF= Charge connection= OFF.

The problem with the diode is it will decrease the voltage being applied to the toad battery by about 0.7 volts. That diode voltage drop along with the voltage drop in small wiring is unlikely to fully charge the toad battery. It will probably help prevent the toad battery from being discharged by its loads, but I wouldn't count on it to charge the battery properly.

If 14 gauge wiring is used, the resistance is about 0.0253 ohms per 10 feet. That means that 20 feet of 14 gauge wire with 10 amps flowing through would drop the voltage another 0.76 volts. Now with a diode you have dropped the voltage by about 1.5 volts, so in reality, you will never see the 10 amp charge rate. And we haven't even considered any ground circuit voltage losses.

Smaller gauge wiring would help the situation. 10 gauge wiring is about 0.00989 ohms per 10 ft., so 20 feet of wire would only drop about 0.2 volts with 10 amps of current.