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05-08-2021, 05:20 PM
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#1
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Senior Member
Newmar Owners Club Spartan Chassis
Join Date: Jul 2012
Location: Manitoba, Canada
Posts: 549
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Toad Charge Line
I just finished installing a charge line between my RV and Toad and am puzzled by the voltage readings I am getting when hooked up. Readings as I expected them to be with either end open but I'm not getting the readings I expected when hooked up at both ends.
I bought the diode (rated for 60 amps) at "Start & Charge" a local business that rebuilds starters and alternators.
Any thoughts on why this would be?
__________________
Jake
2005 DSDP 4024, Cummins ISL 370, Spartan MM Chassis / 2018 Ford Taurus, Roadmaster Base Plate, Blue Ox Aventa LX Tow Bar, RVI 2 Brakes
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05-08-2021, 05:39 PM
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#2
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Senior Member
Join Date: Jul 2014
Posts: 35,317
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Diodes have a voltage drop thru them. The one your using seems high.
Replace the diode with a relay, controlled by the RV key.
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05-09-2021, 12:28 PM
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#3
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Senior Member
Join Date: Mar 2019
Posts: 5,625
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Quote:
Originally Posted by jarwiebe
I just finished installing a charge line between my RV and Toad and am puzzled by the voltage readings I am getting when hooked up. Readings as I expected them to be with either end open but I'm not getting the readings I expected when hooked up at both ends.
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The standard voltage drop for a silicon diode is 0.6 to 0.7 volts so your readings are right where they should be. Most people never check so they assume a diode is like a wire but only passing current in one direction. Not so.
Are you actually measuring the voltage on both ends? If so, put one probe on each side of the diode when it's all hooked up and you'll see the actual voltage drop through the diode.
Ray
__________________
2020 Forest River Georgetown GT5 34H5
2020 Equinox Premier AWD 2.0L/9-speed
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05-09-2021, 12:49 PM
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#4
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Senior Member
Join Date: Jun 2012
Location: The Bluegrass State
Posts: 8,882
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It is my thought that using a diode isn't necessary in most situations especially if you or the chassis builder uses a relay that is only activated when the coach ignition is on. Current will only flow from the higher voltage to the lower voltage batteries.
__________________
Good Luck, Be Safe and Above All, Don't Forget To Have Fun
Pete
Central Kentucky
2006 Fleetwood Discovery 35H, 2014 Honda CR-V, M&G Engineering Braking System
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05-09-2021, 01:09 PM
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#5
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Senior Member
Newmar Owners Club Spartan Chassis
Join Date: Jul 2012
Location: Manitoba, Canada
Posts: 549
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Quote:
Originally Posted by NXR
The standard voltage drop for a silicon diode is 0.6 to 0.7 volts so your readings are right where they should be. Most people never check so they assume a diode is like a wire but only passing current in one direction. Not so.
Are you actually measuring the voltage on both ends? If so, put one probe on each side of the diode when it's all hooked up and you'll see the actual voltage drop through the diode.
Ray
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Thats good to hear. Yes, I checked voltage at both ends. I'll check voltage across the diode next time I hookup.
__________________
Jake
2005 DSDP 4024, Cummins ISL 370, Spartan MM Chassis / 2018 Ford Taurus, Roadmaster Base Plate, Blue Ox Aventa LX Tow Bar, RVI 2 Brakes
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05-09-2021, 02:06 PM
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#6
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Senior Member
Join Date: Mar 2019
Posts: 5,625
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Quote:
Originally Posted by jarwiebe
Thats good to hear. Yes, I checked voltage at both ends. I'll check voltage across the diode next time I hookup.
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The way you did it is OK but an undersized ground wire or charge wire can cause low voltage at the car side as well, if the car actually needs amps from the motorhome at the time of measurement.
An Equinox probably is the poster child for that. My 2020 draws almost 8 amps out of the battery when configured for towing, far more than other cars. Unless the charge and ground wire are at least 14 AWG and preferably 12 AWG, the Equinox will actually slowly discharge while being towed.
Ray
__________________
2020 Forest River Georgetown GT5 34H5
2020 Equinox Premier AWD 2.0L/9-speed
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05-09-2021, 04:38 PM
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#7
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Senior Member
Newmar Owners Club Spartan Chassis
Join Date: Jul 2012
Location: Manitoba, Canada
Posts: 549
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Both my positive and negative wires are 12 gauge so wouldn't expect any significant loss there.
__________________
Jake
2005 DSDP 4024, Cummins ISL 370, Spartan MM Chassis / 2018 Ford Taurus, Roadmaster Base Plate, Blue Ox Aventa LX Tow Bar, RVI 2 Brakes
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05-09-2021, 08:29 PM
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#8
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Member
Join Date: Oct 2020
Posts: 76
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Quote:
Originally Posted by Bigd9
It is my thought that using a diode isn't necessary in most situations especially if you or the chassis builder uses a relay that is only activated when the coach ignition is on. Current will only flow from the higher voltage to the lower voltage batteries.
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I didn't put a diode in mine.
I did, however, add a 15A circuit breaker.
__________________
2015 Fleetwood Bounder 35K
2021 Jeep Gladiator toad
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05-09-2021, 09:07 PM
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#9
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Senior Member
Newmar Owners Club Spartan Chassis
Join Date: Jul 2012
Location: Manitoba, Canada
Posts: 549
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I put in a 20 amp auto reset breaker at the RV battery end and the diode at the toad battery end of the charge line.
__________________
Jake
2005 DSDP 4024, Cummins ISL 370, Spartan MM Chassis / 2018 Ford Taurus, Roadmaster Base Plate, Blue Ox Aventa LX Tow Bar, RVI 2 Brakes
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05-09-2021, 09:27 PM
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#10
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Senior Member
Join Date: Jun 2016
Location: SW Louisiana
Posts: 8,824
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I have both a diode and a 15 amp auto reset breaker on mine, partly the diode is insurance to keep the pins on the 6 way connector at the front bumper from potentially shorting out if exposed to mud, etc. and draining the Jeeps battery. Also the diode will lower voltage and therefore lower battery charge rate on the TOAD if the battery were to be partly drained before connecting, and therefore limiting the chances of tripping the 15 amp auto reset breaker. I am not trying to charge the TOAD battery with the Charge line, just maintain it at a reasonable level.
__________________
2002 Safari Trek 2830 on P32 Chassis with 8.1L w/ 400 watts solar 420Ah LiFePo4
2017 Jeep Cherokee Overland & 2007 Toyota Yaris TOADs with Even Brake,
Demco Commander tow bar and Blue Ox / Roadmaster base plates
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05-10-2021, 04:51 AM
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#11
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Senior Member
Join Date: Nov 2006
Location: Western NY
Posts: 6,113
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I'm not a fan of auto reset CBS.
See
https://www.irv2.com/forums/f85/battery-charging-wire-to-toad-535618.html
Post #3 for details why.
Manual resets work in most cases and I've never had a trip. Worst that happens you have a low batty but with auto resets it can bevfar worse.
__________________
Don & Marge
'13 Newmar Ventana 3433 - '14 CR-V TOAD
'03 Winnebago Adventurer 31Y - SOLD
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05-10-2021, 08:58 AM
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#12
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Senior Member
Join Date: Mar 2019
Posts: 5,625
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Quote:
Originally Posted by Bigd9
It is my thought that using a diode isn't necessary in most situations especially if you or the chassis builder uses a relay that is only activated when the coach ignition is on. Current will only flow from the higher voltage to the lower voltage batteries.
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You're right, it depends. The Ford F-53 gasser chassis (mine is a 2019 chassis) has the charge line available 24x7 on the 7-pin connector whether the motorhome is running, turned off and parked in the desert for a month, or whatever.
My car had some weird OBDII codes once. The dealer in Nashville, where they work on a lot of toads for people passing through, said that is not uncommon for cars being towed. He suggested adding a diode if we start the motorhome with the car connected. That keeps the drop in the chassis battery of the motorhome during the start cycle from pulling the car battery down and then bouncing the car battery voltage up as the motorhome starts.
We do start the motorhome with the car connected at fuel stops, rest areas, and usually on one-nighter's.
If you're plugged into shore power overnight, having the 7-pin charge line powered up all the time can be good as it keeps the toad battery topped off.
I don't obsess over the toad battery charge line voltage. As long as the charge line is sufficient to keep the car battery from running down while towing, and 12.8 VDC does that, I'm happy. Even 12.5 or 12.6 VDC is fine with me.
I'm actually happier with the diode voltage drop because the motorhome's alternator voltage regulator has no idea what the car battery voltage is nor does it care, unlike the car's alternator voltage regulator.
Ray
__________________
2020 Forest River Georgetown GT5 34H5
2020 Equinox Premier AWD 2.0L/9-speed
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05-10-2021, 03:08 PM
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#13
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Senior Member
Join Date: Jun 2012
Location: The Bluegrass State
Posts: 8,882
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Quote:
Originally Posted by NXR
You're right, it depends. The Ford F-53 gasser chassis (mine is a 2019 chassis) has the charge line available 24x7 on the 7-pin connector whether the motorhome is running, turned off and parked in the desert for a month, or whatever.
My car had some weird OBDII codes once. The dealer in Nashville, where they work on a lot of toads for people passing through, said that is not uncommon for cars being towed. He suggested adding a diode if we start the motorhome with the car connected. That keeps the drop in the chassis battery of the motorhome during the start cycle from pulling the car battery down and then bouncing the car battery voltage up as the motorhome starts.
We do start the motorhome with the car connected at fuel stops, rest areas, and usually on one-nighter's.
If you're plugged into shore power overnight, having the 7-pin charge line powered up all the time can be good as it keeps the toad battery topped off.
I don't obsess over the toad battery charge line voltage. As long as the charge line is sufficient to keep the car battery from running down while towing, and 12.8 VDC does that, I'm happy. Even 12.5 or 12.6 VDC is fine with me.
I'm actually happier with the diode voltage drop because the motorhome's alternator voltage regulator has no idea what the car battery voltage is nor does it care, unlike the car's alternator voltage regulator.
Ray
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Thanks for that information. I'll squirrel it away in my brain for future reference.
BTW, if someone (who will remain nameless since I'm married to her) accidentally leaves the toad ignition on while stopped for a overnight, and then try to start the toad the next morning to 'run it through the gears', well....... ...when one of us did that it popped the fuse because the Honda was trying to draw starting current from the motorhome batteries! Now I hate to say she is a slow learner, but twice in one trip OK, I better quit before she reads this or else
__________________
Good Luck, Be Safe and Above All, Don't Forget To Have Fun
Pete
Central Kentucky
2006 Fleetwood Discovery 35H, 2014 Honda CR-V, M&G Engineering Braking System
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05-10-2021, 03:17 PM
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#14
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Senior Member
Join Date: Mar 2017
Location: Sedalia, CO
Posts: 315
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This is the direction I took (used 10ga wire):
__________________
2022 Winnebago Ekko (E22/T21): 2 Lithionics Batteries, 3 Solar Panels, StarLink mobile, Falcon 3.0 Shocks, Sumo Springs, And Tucker
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