Winch wiring question (12V)

Anonymous Poster · Dec 14, 2002

Gary, swing back by the Marine Dealer and ask them if they know what a Tekonsha 2011 is. Distributor price is 8.36 in my book.
I don't have the pinout chart handy for 7 pin connectors, but if memory serves, the large center pin is supposed ot be used for charging the battery.

bgott · Dec 14, 2002

http://www.marksrv.com/wiring.htm

Here is the pin chart for a seven way connector.

stevepio · Dec 15, 2002

Diode voltage drop is the very reason I don't use an isolator for the second battery in my truck. I use a nice, low tech solenoid (big relay). Looks just like a plow solenoid but rated for continuous duty. Lots of current, no voltage drop. It's "on" with the ignition so I have isolation when the truck is off and charging when it's running.

While kind of technical, TT is right on with his dissertation about diodes.

bgott · Dec 15, 2002

A Ford starter relay ought to work just fine for that.

Anonymous Poster · Dec 15, 2002

Ford starter relay will work for about 1 hour till it smokes. They aren't made for continuous service.
The Diode argument don't hold water guys, I did some testing, and with the alternator running, voltage to the battery behind the diode is 14.4 volts.
By the way, for small gel type batterys, we also include a current limiting resistor to prevent cooking the battery.

TWINKLE_TOES · Dec 15, 2002

The Diode argument don't hold water guys

There is a whole bunch of folks that make their living selling stuff to solve this problem. Lets wait until after Xmas to break the bad news.

voltage to the battery behind the diode is 14.4 volts.

Not sure what you mean here by "behind the diode". If you mean the alternator side of the diode (anode)this is normal. If you mean the battery side of the diode(cathode), I suspect you didn't have the battery connected and your high impedance voltmeter does not draw enough current to forward bias the diode at the knee where it will drop o.7 to 1.0 volts. If you truly had the battery connected and saw 14.4 at the battery then the alternator output is approaching 15.2 to 15.4 volts. This is way to high and will boil the main battery away.

I think I have beat this horse to death and will leave it at: two kinds of people on TBN, those that think there are two kinds of people on TBN and those that don't.

Anonymous Poster · Dec 30, 2002

Well Twinkle, following your advice, I doublechecked meter readings several times, and my readings are right.
Then, I consulted a fellow who knows a bit more about automotive charging systems than I do, and he sent me the following information. Batteries:

Typical autos and trucks have 100A alternator. After you start your car within 15 minutes the charge rate reduces to 5A or less.
Assuming you had a trunk load of bad batteries that drew a 5A charge at 14.7V you could float 19 batteries.

The charging system has a fixed voltage.

The amperage a battery draws is dependent on it's state of charge and how badly sulfated it is (SG of the cells). The one battery will not affect the other. Even without an isolation diode the charging system merely sees a larger battery (more plate area).

The isolation diode will drop 0.75V, so the second battery will be exposed to 0.75V less than the vehicle starter battery. As most charging systems are set at about 14.7, this would mean the second battery would see 14V.

The 14V charge level is more than adequate to fully charge any lead acid battery and will overcharge them if left on long enough. Float levels are 13.2 for flooded cell batts.

BUT

You cannot expose a VRLA (small battery with no vent caps, sealed) to voltages higher than 13.8V. They float at 13.2V. Charging voltages are 13.5 to 13.8.

Soooooooooooooo if you connect your 7AH lantern batt through an isolation diode to your car it will merely take a little longer to self-destruct from the excessive voltage.

Those little batts require special chargers as automotive chargers are too hot for them. They will begin to gas and vent needed water and acid.
======================================
Now, in case I forgot to mention it previously, my lantern charging systems employ a current limiting resistor to prevent battery cook down.
So, Twinkle my boy, next time you are hot to trot to tell somebody something they have done for years isn't going to work because you learned something in school, be prepared to get your books handed to you.
Happy New Year.

ISOLATION DIODES:

Are only needed in systems where the starter battery must not be
drained
by any load when the engine is not running.

A boat for example will have starter and house batteries. The house
batteries run the convenience loads when the engine is shut off.
Should
they completely drain by accident, the isolation diode will have
prevented the starter battery from draining.

TWINKLE_TOES · Jan 2, 2003

A battery charged to one diode drop below the main battery is ~ a 50% capacity battery, not good for a winch application.

Franz this was my original post. Read the words "not good for a winch application"

Where in this did you read So, Twinkle my boy, next time you are hot to trot to tell somebody something they have done for years isn't going to work because you learned something in school, be prepared to get your books handed to you.

As for handing me my books I think maybe you should carry them a little longer, maybe even read them.

I stand by my second post:

You can lead a horse to water....

Phred · Jan 3, 2003

Franz & Al,

I agree with Al on this one.

If you measure the voltage from the battery at the output of the diode you will get the full ~14 V.
However, when you start to draw current into a battery throught the diode, the diode will be biased and you will get the ~0.7V drop.

<blockquote>In reply to:<hr>

Some isolators use Schottky diodes with lower forward voltage drops (0.4 to 0.6 volts)at the expense of high reverse leakage and lower breakdown voltage, but the payback is small and there are better ways to work this problem.

<hr></blockquote>

Al it seems that a schottky device would help. 14.4 -0.4 gets you just above the 13.8 you need?
Also some of the newer schottkys are closer to 0.3V.

If you use a diode consider the current requirements. If its just charging then no big deal but if you want to power a load the diode(s) must be able to handle the full current load.

Fred

TWINKLE_TOES · Jan 3, 2003

Fred,

The point I have been trying to make (somewhat unsuccesfully)is the automotive charging system (constant voltage) is ill suited to recharge batteries that have a deep depth of discharge as in a winch application. For the application they are designed, replenishing the charge removed by short term loads like starting, the system obviously works OK.

At the risk of introducing some "book learning" the following link is offered. <A target="_blank" HREF=http://www.batterytender.com/catalog/chargingbasics.html>Battery Charging Basics</A> You can see from this that proper charge of a lead acid battery is a complex process.

One thing this link neglects is the battery voltage dependence on temperature. Lead acid batteries have a negative voltage temperature characteristic. All of the voltages identified by this link are for ~ 25 deg C.

This dependence is - .005 Volts/cell-deg F, or for six cells about 30 mv/deg F. All of the voltage values in this link should be corrected by this factor.

The following table for example reflects the absorption voltage temperature depencency.
Temperature F/C Absorption Voltage
122/50 13.80
104/40 13.98
86/30 14.19
77/25 14.34
68/20 14.49
50/10 14.82
32/0 15.24
14/(-10) 15.90
(-4)/(-20) 17.82

Al it seems that a schottky device would help. 14.4 -0.4 gets you just above the 13.8 you need?

It will certainly help but still does not overcome the short comming of a constant voltage charging system. It will provide acceptable performance in an application like a camp trailer where the depth of discharge is small and replenished the next day on the road. The shortcomming of the Schottky diode is low reverse breakdown (in the order of 40 to 50 volts) Motor loads with inductive spikes can easily exceed the diode maximum reverse voltage.

Many manufacturers offer products to solve this problem Trace Engineering, Balmar, Ample Power and Guest are a few.