Toad battery charging

[BigTexEd]

Hey guys. No big deal. Thanks for your input. I’m not setup for these forums. Good day.

[Morich]

There seems to be a lot of the fine points missing on this question and it is not all on either side. It looks to me as if you are starting with some really bad info on your first post, so let me see if what I am reading and understanding is what you meant.

It really seems you are making your setup much more difficult than needed, so rather than debate who is right or wrong, perhaps I can just throw in my thoughts and see if it fits what you know.

Quote:
1) Using the charging wire (#4) from the 7 pin trailer connection. The MB Sprinter chassis manual says to NOT use this for charging the battery under tow. I can see multiple problems with this. a) Manual says not to use it. b) It is not regulated. c) No protection for anything (under volt, over volt, short circuit). This can/will lead to damage to the toad battery, coach wiring, or anything in between.

I can fully agree that the book may say what you state. No questions there.
B. You say it is not regulated but doesn't the alternator take care of regulation?
C. No protection ? What protection is needed for undervoltage as the fuse in the RV that powers this circuit will blow if the amperage goes too high, where would one get overvoltage in an RV that would be higher than the toad is designed to handle? Unless we cross with the 110 Ac, isn't the alternator output going to be as high as the voltage gets? A fuse is the protection for a short circuit and there is a fuse at each end of the wiring.
The concern about high current flow is missing the basics of WHY that current flows. Current flows due to the difference in potential between two points and we normally reference it from ground or zero potential. Take a 14-15 volt input and ground it to zero and lots of current flows to blow the fuse. But in charging a battery, we rarely would try to charge a battery reading zero but more often in the 6 volt or higher range which means the difference in potential from the alternator and the dead battery is not 14-15 volts but more like 6-8 volts and much less current will flow and only for a short time. We know the battery charging is a slow chemical reaction that may take 8 or more hours and we also know that we will find a surface charge on a battery when it is on charge.

This all gets down to the first bit of current may be as high as 6-8 volts but it quickly dropped as the surface charge builds and the difference in potential gets much lower.

On our RV, the first few minutes after starting, the output voltage of the regulator is high and often in the 14 volt plus area due to the battery being somewhat low after turning the starter but that battery quickly begins to go higher and the regulation in the alternator reduce the voltage which in turn reduces the current.

I use the RVI Brake battery charger setup and it does nothing for regulation as it is simply a set of wires going into a diode and an LED with another set of wires going out to the battery. I took it apart to see why I needed it and it is mostly empty space! There is a new model which does let us monitor the current flow but that really doesn't do anything that I need as my battery charging voltage/ current are already regulated by the alternator.

When we hook a toad on to charge the battery it is no more, nor less than what we do when the coach and start battery are connected together through the mode solenoid as we drive the RV!

[BobC]

Morich-

As usual, I agree with your comments. I'm disappointed that the RVI unit, which I have, is just a diode and LED. I'd have expected more for that price.

With my 2011 Honda Odyssey, which officially can't be flat-towed but unofficially can, a low or failed battery can be fatal to the transmission. I also have a Honda 5 that can't be flat-towed, officially or otherwise. For these reasons, I've ordered an Acme tow dolly even though the Honda is equipped for flat-towing. My wife is in a wheelchair so our choice of toads is limited.

I've only towed the Honda a couple of times and, even with the RVI unit, it acted like the battery was low when I started it after towing.

When I bought my MH, a PO had screwed up the wiring so I added it the charging circuit using 10 AWG wire. In any case I'm going to have to do some testing.

If I do flat-tow the Honda, I'd like to have some way to monitor its state of charge from my driving position. Ideas?

[Morich]

State of charge is kind of weird and depends on what we each use as a reference/starting point to judge the state of charge. Kind of reminds me of human temperatures or blood pressure!
On us we use 98.6 as the normal expected temp but we know it is different for different situations and even different people. So we get the same for batteries as they vary kind of like people. Sometimes the lead, acid or some small point is just a little different and a battery may work a little better or worse.
I use specific gravity of each cell as the closest way to judge a battery but that is just really not practical, so we use the voltage over the six cells of the battery and say it should be some number, even though we know that number is more an average expected than what we might find. Pretty good and good enough for most uses!
We can move to newer, more complex things like the newer RVI Battery Maintainer which can go wireless to our phones but at the added disadvantage of using more power and being more expensive!
Big point to me is that we are not actually trying to charge the battery on the toad, just "maintain" it, so we don't expect much draw as the taillights and other things are powered through other wiring or separated and we are just powering the brake box in lots of setups. If we pull a 12.8 charged battery up and connect it to the 12.8 battery in the RV which has the 14.5 from an alternator charging it, we don't get much flow at the toad battery except what the brake box is using and that normally just sets there and doesn't brake except in really hard braking. If my car breaks away, I want it to stop but it mostly just sets there! Maybe I'm missing the tablet showing it is braking but I have not seen it at any time.
One way to monitor the voltage would be to run a set of wires to a small volt meter near the dash. This would not be a "real number" like 12.8 due to some drop in the reading along a pretty long run of wire, but it would be like our body temperature reading, in that we could say some really far off reading of 10.6 was normal for the dash reading when we know that a reading at the battery is 12.8!
What I'm saying is that we can get way too hung up on what we should see and we are often talking about the difference in potential (voltage!) as referenced to ground. But that doesn't have to be true as we can also refer to the difference in a voltage as compared to another voltage.
We could say the RV battery is only .6 volts ---if we agreed that we are comparing it to the voltage of the tow battery!
So if we were concerned enough to need to know the tow battery voltage, we could use a simple cheap meter and set a new "standard" reading and then if it moved off that standard, we could assume we needed to check.
This is one which I have in several different uses as being so cheap that there is no reason not to!
One use is to let me see what the RV charge systems are doing. The actual readings from both battery strings are not the "true " reading I get at the battery but they do give me a reference point to judge when it goes up and down.
Pretty much like a blood pressure reading that we know may be a bit high but goes up and down all the time so we use it to give us a reference in case it begins to go further and further off "normal"!
https://www.ebay.com/itm/0-28-Inch-2...wAAOSwsaxfrvlL

Once you have a reading and know it is good, it just takes a mental adjustment to know that a battery reading at that point of 10.3 might be okay but getting a reading of 10.0 might need checked. Let 10.3 at the dash mean okay when you check at the battery and have 12.8?

[patoc]

I use a Patriot brake assist for our Jeep. I use the power from the Vista as the source for the Patriot. I ran a line to the sidewall of the cabin by the clutch pedal, and attached it to a cig lighter. When towing, I just disconnect the Jeep battery, leave the ignition switch on to free the steering wheel, and we're off and running.

Using the rig's power simplifies the process. What am I missing?

[Fritos55]

I’ve been looking at the same issue, as I have drained the battery on my toad a couple times. I’ve been looking at the RVi Towed Battery Charger Plus. According to the RVi web site: “The Towed Battery Charger Plus is an on-demand system that not only trickle charges vehicles that have little draw, but can charge up to 10 amps when there is a high parasitic drain on the battery when flat towing.”

I’d be interested in hearing what you end up doing and how it works out for you.

[Pdest]

I have used the RVI towed charger in three vehicles with no problem. It is a trickle charger with 10 A max output. Just make sure your pin 7 wire is 14-16 gauge and you use the included in-line fuse to prevent over current on pin 7 wiring.

[Winterbagoal]

Originally Posted by patoc

I use a Patriot brake assist for our Jeep. I use the power from the Vista as the source for the Patriot. I ran a line to the sidewall of the cabin by the clutch pedal, and attached it to a cig lighter. When towing, I just disconnect the Jeep battery, leave the ignition switch on to free the steering wheel, and we're off and running.

Using the rig's power simplifies the process. What am I missing?

Sort of off topic, but does your 2002 Wrangler have locking steering? My 2016 doesn't, and I had to clarify that before I tried towing it. My dealer's patriarch told me I'd have to put the key in the ignition to free up the steering, but that clearly wasn't the case. He was a nice guy, bit of a character, but stuck in the '70s. I always got along with him, and his sons, who actually ran the business.
They did the Blue Ox install, everything, including wiring, and I charge from the umbilical, the dreaded pin #4, and have done so for 2 years. No problems, AGM chassis battery, not a "deep cycle" as some have suggested, and also charging 2 X 100Ah LiFePO4 coach batteries, and I'm always ready to go at the destination. No struggle to start the Wrangler. Fires right up.
This sounds a lot like the "you'll blow up your alternator, if you try to charge lithium with it" threads. That might be a possibilty, if your lithiums are drained to almost zero SoC, but highly unlikely in the real world. If you start with a fully charged towed battery, hours of driving, even at 3 amps, is probably more than enough to keep your towed's battery charged, unless you started with a dead one.
I'll add "yes" to Morich's comments. Common sense, mixed with some technical expertise, and some real world experience, as usual.

[Retired FF]

Originally Posted by Winterbagoal

Sort of off topic, but does your 2002 Wrangler have locking steering? My 2016 doesn't, and I had to clarify that before I tried towing it. My dealer's patriarch told me I'd have to put the key in the ignition to free up the steering, but that clearly wasn't the case. ... If you start with a fully charged towed battery, hours of driving, even at 3 amps, is probably more than enough to keep your towed's battery charged,
I'll add "yes" to Morich's comments. Common sense, mixed with some technical expertise, and some real world experience, as usual.

I have been on forum but rarely ask questions. 2012 Itasca Class A 26P Sunstar V10 w/ 1996 Geo toad: thank you I was getting lost in the techy speak.

Geo is simple, main disconnect electrical installed on bumper, #12 from correct pin (reverse mirror image at toad) to toad battery w/ auto reset 15 amp breaker and diode to prevent any feedback to MH, powers Invisbrke unit and MH LED indicator from toad brake switch w/ its' diode. Alaska to Florida Everglades with no problems. I was getting a little nervous with the discussion. Do you foresee any problem?

Jeep question from what appears to be your experience, attempting to replace poor twice rebuilt Geo w/ Wrangler. Disconnect power, transfer to neutral, AT to Park, key on ignition release steering lock, travel forward! Unfortunately the Jeep dealer's information does not build confidence. What Wrangler years can be towed four down similar to Geo setup? Wasn't familiar with any years steering column remained free without ignition on (interesting nobody has mentioned that). Does disconnecting battery for towing remove transmission/engine ECM memory/settings? Haven't found anyone willing to discuss ABS? Regardless of Jeep manuals, definitely don't want lift shift cover, push some magic button, place transmission in neutral, then shift to park. Old guy, give me a neutral transfer case position that I cannot screw up on a dark rainy night hook-up.

I don't expect all that research from you, looking for an honest experienced forum or association that has the time to discuss options. Thank you again.

[Morich]

I have no experience with the Jeep world but the electrical charging for batteries is often what I see as way overblown as a worry. We have towed several cars from a 98 ford Escort which was very simple to put in neutral and go with the lights wired direct off the hitch and the tow battery charge from the RVI brake battery maintainer doing everything we needed. Next was a 2015 Focus wired much the same on lights and battery charge but with an electronic transmission which requires total electrical cutoff to make it not try to shift. That portion required a solenoid or removing the battery negative lead. That left the maintainer only keeping the battery up for the small power used by the brake box.
The new car which we just got wired is a 2018 Honda HRX with manual transmission to make it easier to set up as it only requires going to neutral and first click on the key which makes sure the wheels do not lock on corners.

But none of the cars have ever been a problem with charging as it is really not something that should ever involve heavy charging as the car battery is assumed to be near full charge when we start it and run it up to hitch on. That means the wiring built into the RV hitch and meant to recharge boat batteries, etc. is designed and wired to do the small charge on our use without any worry.
It kind of seemed the OP is making assumptions on things like fuses, power needed and current flow without really stopping to think what the power point on the hitch is meant to do. If it is meant to handle all the electronics on a big bass boat, my poor little Honda has nothing to worry about!

[BadMed]

I called Winnebago and asked if they thought is was OK to charge the Toad battery from the charge line running to pin 4 of my 202 View's 7-pin socket. I also pointed out to them that the MB Chassis manual says NOT to charge a battery on the charge line provided. Winnebago said there would be no problem to charge the Toad battery as long as the battery did not have low voltage, in other words, it is OK to maintain the Toad's battery. I crawled under my 2020 View and found the charge wire running to pin 4 is 12 AWG and the Chassis battery is about 19 feet from the socket. I am using a RVi Toad Battery Charger which limits the amps to 10 and will trickle as needed. When I connect the ambilocal cord between the RV and Toad I check the indicator lights on the battery charger that show the status of the toad battery. Every time I do this it has shown the toad battery is above 12 volts, so the charger will be drawing very little amps to maintain the battery. Right? If the toad battery ever showed below 12 volts I would probably hook it up to a 110V battery charger until it reached 12 volts. Any thoughts on this plan?

2020 View 24D

[Morich]

We often get folks who are missing the basics of why current moves in any circuit. They get highly involved in lots of techie things and forget that the REASON for current to move is there is a difference in potential at tow points.
We call that potential voltage, so when we speak of any circuit that has a given amount of resistance, whether the resistance is from long thin wires or just the items we are run to like trailer lights and battery, we normally assume that resistance will stay near the same.
Using Ohm's law, we can say that the current through a circuit will be directly related to the voltage and resistance, so if we drop the voltage, the current is will also drop.

That means if we run 12volts from the RV and screw it up so that the trailer end is ground, there is a difference in potential of 12 volts and we get lots of current flowing! We normally get enough to blow a fuse, so we don't do that! The 12 volt to 0 volts as we call ground is a lot and we get a lot of current!

So when we hook a car up to tow, we need to look at what is different. The RV battery I've been calling 12 volts is the same and the resistance in the wiring to the plug, etc. is the same, but the DIFFERENCE in potential from one end to the other is far different as we are not grounding the end but tying it to a tow battery which is often near the same 12 volts as the RV battery.

Just for giggles lets say the tow battery is run way down to 11 volts? So what is the difference from RV battery to tow battery? The answer is pretty simple and you DO NOT get much current flowing from one volt!!!

Don't worry the details too much but just know that the RV alternator does vary the voltage up and down and it may be putting out as much as 14. 5 volts and that is fine with charging the start and coach batteries. The tow system is the same and that is fine.
The difference in charging the tow battery from the RV charge system is little different than charging it from the tow alternator and both ways work pretty good.
If you have a totally run down battery on the tow car and you have to push it to get it hooked up, you may find the current is higher than the hitch connection is fused and it may blow the fuse but if you start the tow car and drive it to hook up, the battery voltage of the two is going to be pretty close and no problem!