Battery Drain When Travelling - Power Converter Issue?

[ZekenSpider]

Originally Posted by Padgett

Except that is allowing for the return also: =IF($B$7>0,($B$6*C$19*$B$5*2/$B$7),"") b7-# conductors, b6-amps, c19-ohms/ft, b5-length

E=IR Since b7=1 (solid core) we can drop that factor

Voltage loss a single conductor for 20 ft of #12 at 20A is .65v 10ft of #10 is .20v = .85v

Agree the Bargman must be spiffy both for the 12v and the ground (cannot rely on trailer to hitch ball).

Bottom line: Charge the battery before you leave and rely on the TV just to maintain the charge. I also carry a generator if not guarenteed power.

ps in another lifetime at the swamp in the 70s one of the interesting questions was "If the A-12 was retired and F-12 cancelled, why were we still building J58s ?"

BUT.... b7 is the number of conductors ONE WAY (and I do not mean stranded versus solid). You must allow for the return resistance, you cannot ignore it. If you fail to account for the energy lost going back to the electron pump(the alternator) you are missing at least half of the energy loss .

In your discussion, you have assumed that the total resistance of TM frame, all of the frame ground wires, the negative return wires thru the Bargman and the TV frame to the alternator is zero...and it can not be zero. It is always something. It is at least as much as that in the Positive pole to the battery. The excel formula assumes resistance in the return (Negative) pole is equal to that in the supply (Positive) pole.

That's close enough for most discussions but my experience with poor frame bonding tells me that the frame return resistance is usually greater than the supply path resistance.

The goal of the circuit we are discussing here is to provide sufficient power (volts x current) to charge the battery. Some of the power is lost in the positive pole wiring from the alternator to the battery and some of the power is lost in the negative pole return to the the alternator. The result is a lower delta V across the battery than desired and therefore a lower charging current. This a series DC circuit. The charging current will be controlled by the total resistance, not the supply conductor only.

IMHO.

I agree with your bottom line though and it looks like I left the swamp a few years before you did.

Jerry

[ZekenSpider]

Originally Posted by YNPKing

Great discussion, thank you. I decided to supply this additional information (particularly, in light of the discussion on VD) to see if it alters your thoughts on charging the batteries while traveling with the fan and Dometic RM2354B refrigerator running on DC.

Given the following:
TV: 2014 Jeep GC alternator 220-amp; TM: 2014 TM 2417 Sport; Bargman to WFCO WF-8955PEC converter is ~20ft @ #12 wire (per schematic); converter to (2) 6V Lifeline AGM batteries is ~10ft @ #10 wire; Dometic ~halfway between converter and batteries.

Batteries tested with voltmeter:
13.03V - Pulled out of TM, fully charged (several days), rested 2 days (No surface charge). It actually took 2 days to remove the surface charge.

TM cables tested w/o batteries:
12.71V - w/ Bargman connected; Jeep off
14.16V - w/ Bargman connected; Jeep idling
14.18V - w/ Bargman connected; slight rev of engine

Batteries connected in TM:
12.99V - w/o Bargman
12.91V - w/ Bargman; Jeep off (reverse current flowing to Jeep?)
13.00V to 13.83 - w/ Bargman; Jeep idling (interesting, as I watched the voltmeter climb in .01V increments until it stopped; no dramatic jumps)

Dan

Dan;

I'll try to draw up a simple schematic of your Jeep to TM 12 V DC circuit with the numbers you have observed. I know exactly what you are running into and what it will take to change it. It's quite a bit of work to change it and I have decided to ignore it on my Suburban to 3326 application. I always tow with the refrig on DC (10.6 Amps). I have an 85 watt solar panel that assists charging (not much though... about 2 amps). When I park for lunch I disconnect the Bargman so it will not pull down my TV battery.

Buy the time I have towed for 6 hours or so the TM battery has dropped to about 12.2 volts. When I get set up in camp and can connect shore power the battery monitor that I have reads 60 % discharged and the converter starts charging at 7 amps or so. It takes about 10 hours to recharge.

Incidentally, regarding the charging circuit while towing, even though the converter is in the 12 VDC circuit it has nothing to do with it until shore power is connected. it is merely connected to the circuit like any other DC component but neither contributes nor consumes energy.

I'll try to post the schematic with a discussion later this weekend.

Jerry

[ZekenSpider]

Originally Posted by YNPKing

Great discussion, thank you. I decided to supply this additional information (particularly, in light of the discussion on VD) to see if it alters your thoughts on charging the batteries while traveling with the fan and Dometic RM2354B refrigerator running on DC.

Given the following:
TV: 2014 Jeep GC alternator 220-amp; TM: 2014 TM 2417 Sport; Bargman to WFCO WF-8955PEC converter is ~20ft @ #12 wire (per schematic); converter to (2) 6V Lifeline AGM batteries is ~10ft @ #10 wire; Dometic ~halfway between converter and batteries.

Batteries tested with voltmeter:
13.03V - Pulled out of TM, fully charged (several days), rested 2 days (No surface charge). It actually took 2 days to remove the surface charge.

TM cables tested w/o batteries:
12.71V - w/ Bargman connected; Jeep off
14.16V - w/ Bargman connected; Jeep idling
14.18V - w/ Bargman connected; slight rev of engine

Batteries connected in TM:
12.99V - w/o Bargman
12.91V - w/ Bargman; Jeep off (reverse current flowing to Jeep?)
13.00V to 13.83 - w/ Bargman; Jeep idling (interesting, as I watched the voltmeter climb in .01V increments until it stopped; no dramatic jumps)

Dan

OK lets see if I can explain what you saw with your voltage readings.

Look at the attached schematic as I refer to certain parts of the sketch.

Given the following:
TV: 2014 Jeep GC alternator 220-amp; TM: 2014 TM 2417 Sport; Bargman to WFCO WF-8955PEC converter is ~20ft @ #12 wire (per schematic); converter to (2) 6V Lifeline AGM batteries is ~10ft @ #10 wire; Dometic ~halfway between converter and batteries.

The amp capacity of the Jeep alternator is not relevant since the TM is pretty much limited to about 30 amps from the TV. You also did not mention the length and size of the wire in the Jeep to the Bargman. I assumed 15' of #10. The Converter is also not relevant to the conversation except as a tie point for wires. It neither contributes or subtracts from the TM DC system unless it is plugged into shore power.

Batteries tested with voltmeter:
13.03V - Pulled out of TM, fully charged (several days), rested 2 days (No surface charge). It actually took 2 days to remove the surface charge.

Pretty much normal. Maybe a little higher than I would expect but not important to the discussion. While in the TM the battery is never disconnected from a load. There is always around 0.5 amps "parasitic" load (radio memory, radio antennae, circuit monitors, etc.). That load slowly drops the battery surface charge voltage and will actually drain the battery (120 Amp-Hour size) in 10 days or so.

TM cables tested w/o batteries:
12.71V - w/ Bargman connected; Jeep off
14.16V - w/ Bargman connected; Jeep idling
14.18V - w/ Bargman connected; slight rev of engine

At 12.71 V you are measuring the voltage of the Jeep battery. Your meter is connected at points E and D in the sketch which then connects your red lead thru the Bargman to point A on the sketch and your black lead thru the Bargman to point 1 in the sketch. There is almost no current flowing from the Jeep to your meter. There is probably 0.5 amps of load flowing from the Jeep battery to the parasitic loads in the TM or more if any other loads are turned on in the TM (tail lights, etc.). My point is that with very little current flow there is virtually no voltage loss. Note the formula for Voltage Drop at the bottom of the sketch. If I = 0, then Delta V = 0.

At 14.16 V you are seeing the Jeep battery under charge from the alternator.
The alternator regulator is attempting to increase the alternator voltage to a nominal 14.3 V ( in your case it looks like maybe 14.2 V is the set point).

At 14.18 V you are also seeing the Jeep battery under charge from the alternator. The alternator regulator is approaching a nominal 14.3 V ( in your case it looks like maybe 14.2 V is the set point).

Batteries connected in TM:
12.99V - w/o Bargman
12.91V - w/ Bargman; Jeep off (reverse current flowing to Jeep?)
13.00V to 13.83 - w/ Bargman; Jeep idling (interesting, as I watched the voltmeter climb in .01V increments until it stopped; no dramatic jumps)

12.99 V is showing the effects of the 0.5 A TM parasitic load. Given enough time it would drop to full discharge voltage (do not let it get much below 12.0 V);

12.91 V could be the effect of reverse flow or the continued discharge caused by TM parasitic loads. It could also be meter inaccuracy.

13.00-13.83 V shows the Jeep 14.16 V is causing flow into the TM battery. The current flow demanded by the TM battery was limited by the resistance of the supply wiring from A to D and the return wiring through the frames from E to 1. As the TM battery became more charged (remember, it takes about 0.7 V to overcome the internal resistance of the battery) the current demanded by the battery reduced. With the TM battery at 12.91 V when you began to charge it, the charging circuit had to crank the TM battery up to 12.91 + 0.7 =13.61 V just to begin charge current flow. If you had waited long enough, they TM battery voltage would have climbed to be equal with the alternator set point of 14.2.

I have run out of time for the next hour or so, so I will continue this later tonight.

Now to continue;

My primary goal is to show why the TM battery cannot be charged by the TV when the Refig and fan are running.

The Refrig and fan both are supplied positive voltage from the TM DC Fuse Block. They both are drained of voltage by the DC ground (Negative pole return)...perhaps a funny way of talking but it provides a better visual image. Both components require current (Amps) to flow in order for them to operate. Anything that restricts current will make them operate improperly.

We can ignore the fan for this discussion since only needs about 0.3 amps. The Refrig, on the other hand, needs about 11 Amps...constantly. 11 A in and 11 A out. The drain ( TM ground wires, frame, Bargman and TV ground, wires and frame) must take away the 11 A and return it to the TM battery or to the TV battery or both.

So let's start with a fully charged TM battery, with the Bargman connected, the Refrig on DC and with the Jeep engine running at idle.

Voltage measured across point A to 1 is 14.2 V. Voltage measured across the TM battery is 13.2 V. 11 A are flowing through the #10 wire from A to the Bargman, from the Bargman to C+, to the fuse block then to the Refrig. 11 Amps are also flowing from the Refrig to frame point 6, thru the TM frame to frame point 4, through the Bargman to TV frame point 3, thru the TV frame to point 1, then back to the alternator.

Now, because of the resistance in the wires and connections from point A to C+ we have less voltage at C+. The calculation for that loss is;

(15 x 0.00102 x 11) + (20 x 0.00162 x 11)= 0.1683 + 0.3564 = 0.5247 V. We need to double that loss because of the return path thru 7, 4,3, and 1. So the total voltage loss is 1.049 V.

Starting with 14.2 v at the alternator we now have 14.2 - 1.05 = 13.15 V available at C. The TM battery is at 13.2 V so now some current also flows out of the TM battery and there is not enough voltage to keep the TM battery charged.

As the TM battery discharges it begins to increase the current flow from the TV to not only give the Refrig it's 11 A but also give the TM battery it's charging current. The lower the TM battery gets, the greater the charging circuit current (from A to C) gets. The result is that the battery voltage drops to nearly full discharge over several hours of this because the A to C circuit gets an increasing voltage drop caused by the increased current demanded by the TM battery.

The only partial solution is to have larger wire in the A to C section, especially in the Bargman to C section. The other part is to have a better ground return in all the frame connections and wire sizes connecting to points 7,5,4,3,and maybe 1.

I hope this is helpful. I may have gone too far into the weeds. Hope not.

Please ask questions if clarification is needed.

Regards,

Jerry

Regards,

Jerry

[Padgett]

Just an observation but the 220A rating is important because that is full charge at about 7000 alternator RPM. What is more important here is the charge at 1500 rpm (idle) to 3500 (65 mph). My experience with an RV that wound about 20% higher at 65 was that at idle a 95A alternator would let the lights dim with lights, wipers, and fridge (compressor) on and that it took a 140A alternator to maintain the vehicle loads at idle.

Point being that an alternator typically is only capable of 20-30% of rating at idle (see enclosed 12SI and CS144charts). My TV has a 160A and that is probably enough.

[ZekenSpider]

Originally Posted by Padgett

Just an observation but the 220A rating is important because that is full charge at about 7000 alternator RPM. What is more important here is the charge at 1500 rpm (idle) to 3500 (65 mph). My experience with an RV that wound about 20% higher at 65 was that at idle a 95A alternator would let the lights dim with lights, wipers, and fridge (compressor) on and that it took a 140A alternator to maintain the vehicle loads at idle.

Point being that an alternator typically is only capable of 20-30% of rating at idle (see enclosed 12SI and CS144charts). My TV has a 160A and that is probably enough.

Of course it's important and you are right that a 160 A alternator is probably adequate for a TM tow package. The battery discharge issue, while traveling with the Refrig on, is not so much an idling RPM issue as it is a cruse RPM issue.

Regards,

Jerry

[YNPKing]

Jerry,
Thank you so much for your responses. I am visiting family in PA this week and part of next week so I won't be able absorb all the info you provided until I get back to FL. If I have questions, I'll let you know.
Thanks to Padgett also. Unfortunately, it's not a TM trip but the leaves have been great.

Dan

[scrubjaysnest]

Originally Posted by ZekenSpider

Of course it's important and you are right that a 160 A alternator is probably adequate for a TM tow package. The battery discharge issue, while traveling with the Refrig on, is not so much an idling RPM issue as it is a cruse RPM issue.

Regards,

Jerry

There is a lot of good info here: http://www.trailmanorowners.com/foru...ad.php?t=10986
about traveling with the refrig on DC. As noted in this thread we didn't use as large of wire as Phillip but always arrive with full charged batteries and a cold refrig.

[tentcamper]

I'm starting to think the way to fix the battery draining issue when traveling, is to isolate the camper battery from the TV. Use the battery charge line as the input to a 12V to 12V 3 stage battery charger? The input side of the charger can be as low as 9.5 V. The other option is to install some very large conductors and a special connector for the TV to trailer?


The problem is these chargers are not cheap when you are looking at 10+ amps? I would think with the fridge running on 12v you would want at least a 15 amp charger.

[Padgett]

The other factor is that electronics needs clean DC power and a plain car battery charger is not (so bad that many modern cars will not run properly if a charger is connected). That is why an RV quality DC power supply is not cheap.

[Bill]

Originally Posted by Padgett

Just an observation but the 220A rating is important because that is full charge at about 7000 alternator RPM. What is more important here is the charge at 1500 rpm (idle) to 3500 (65 mph). My experience with an RV that wound about 20% higher at 65 was that at idle a 95A alternator would let the lights dim with lights, wipers, and fridge (compressor) on and that it took a 140A alternator to maintain the vehicle loads at idle.

Point being that an alternator typically is only capable of 20-30% of rating at idle (see enclosed 12SI and CS144charts). My TV has a 160A and that is probably enough.

Padgett -

Do you know the typical ratio of engine RPM to alternator RPM? In other words, if the engine is idling at 500 RPM, how fast is the alternator turning? Until I know that, I don't know how to use the graphs you posted.

Bill