Using PU truck to charge batteries.

packdaddy

In the event I am out camping and there are several days of cloud and rain... what are the implications for connecting my trucks batteries cables directly to my deep cycle batteries just to get through a long spell of low light.

- Could I use jumper cables and make the connection.
- Would it be best start the truck first then disconnect the truck battery
- would it be OK to keep the cranking battery connected
- How long could I expect to reach full to near full charge. (add another 100 AH)
- At what point voltage wise would it be good to look for an outside source to charge.

If it's not a problem what is the best way. I don't want to buy a generator for a 10 day stay.

---

have 6 x 15watt panels (90 watt) & 2x6v GC batt = 210 AH

PhilS

Re: Using PU truck to charge batteries.

I've seen/heard it said that deep hard charging is hard on an automotive alternator.

I don't recommend disconnecting the starting battery. Yes, start the truck first, then carefully attach the jumper cables in this order: first the cables to the RV batteries, then the positive cable to the truck + post, then the negative cable to a solid metal piece of the engine, away from the battery, for a good ground. There will be a spark at that last connection and you don't want the spark to cause a battery to explode (rare but possible).

I'd do exactly as you are suggesting if I was dry camping, needing to recharge the batteries and didn't have a generator.

As to "how long" it'll depend on how deeply the batteries are discharged and how much your alternator will put into them.

Phil

BB.

Re: Using PU truck to charge batteries.

Never disconnect the truck battery--if the jumper to storage battery connection is opened while the truck is running--it is possible for the alternator to over voltage and take out every lamp and piece of electronic gear in the truck (in the old'en days--we used to run 110 VDC power tools from an alternator converter kit (switch out 12 volt regulator--if I recall correctly).

How long is a guess... When you see the storage battery start to bubble hydrogen gas--it is probably charged enough for your use (longer runtime will only get a little bit more charge at the cost of a lot more gasoline).

If you can, get a hydrometer to watch the battery state of charge.

-Bill

blackswan555

Re: Using PU truck to charge batteries.

You may want to check your trucks charging voltage, Most alternators do not put out what we would call a decent charge voltage, You will also probably have to raise the engine RPM to about 2500 to get much worth having at all, and probably be lucky to see 14v
Have a good one
Tim

Cariboocoot

Re: Using PU truck to charge batteries.

Not the best idea as the truck's system will limit the potential charge Voltage to the deep cycles. Won't hurt the alternator a bit, but once the truck is at 13.8 Volts (roughly - its 'float' setting) that's all you've got; the additional load of the discharged external batteries may not be enough draw to trigger significant output.

Instead of jumper cables, I suggest you make up a 'dedicated' 10 gauge line with Ammeter. For one thing, the clamps are notorious poor connections and you may find the truck running with zero going to the external batteries. For another, you want to watch that output current and see what's going on.

It'll keep them from going completely dead, but it won't supply the 15 or so Volts needed for a good charge of the deep cycles.

BTW, the old mechanical 'cut-out' type regulators were better for this sort of thing.

blackswan555

Re: Using PU truck to charge batteries.

If you have a good auto-electrician around, he may be able to build some sort of resistance into the alternator voltage regulator v sense side to fool it into giving a higher voltage ?
Tim

Cariboocoot

Re: Using PU truck to charge batteries.

blackswan555 wrote: »

If you have a good auto-electrician around, he may be able to build some sort of resistance into the alternator voltage regulator v sense side to fool it into giving a higher voltage ?
Tim

Problem there is over-charging the truck's battery.
There's no good, easy way around this as the 'external' batteries will be further from the charge source and therefor subject to greater Voltage drop through line loss - even if all other factors are equal.

Could run a DC-DC converter and push up to 24 VDC, then re-regulate for the batteries. But what a lot of rig-a-ma-roll that would be!

Brock

Re: Using PU truck to charge batteries.

I was going to suggest a 1500w inverter and a good charger, does the setup already have a 120v charger built in? This would load the truck battery down and the alt will see that load for sure and increase the output. It will also get a true charge to the second bank of batteries. You could put the inverter near the trucks battery and run a much smaller 120v line to the charger. This could also serve as a backup for a home in a pinch.

BB.

Re: Using PU truck to charge batteries.

I am with Brock if you can justify a nice inverter and battery charger for home use. Also works better at charging the RV battery bank on the drive there and back than just connecting to the chassis alternator (and battery isolator/diode block/relay).

-Bill

packdaddy

Re: Using PU truck to charge batteries.

I have also been contemplating an Inverter scenario. Here's what I already have as far as a decent inverter. But I haven't put much thought into how to wire it to the truck yet. (it has a built in charger). The problem with this is it doesn't have a 12 volt input for the charger part of it. I might be able to run my old "Ship to Shore" 10 amp charger off of it.

http://www.aaasolar.com/ProdLit/Trace/DRManual.pdf

The Trailer also has a 3 stage charger tied into it's electrical.
I also have a basic cigarette lighter plug in 750 w car inverter.
A Ship to Shore 10 amp deep cycle / Marine battery charger (not 3 stage)

packdaddy

Re: Using PU truck to charge batteries.

BB. wrote: »

How long is a guess... When you see the storage battery start to bubble hydrogen gas--it is probably charged enough for your use (longer runtime will only get a little bit more charge at the cost of a lot more gasoline).

If you can, get a hydrometer to watch the battery state of charge.

-Bill

BTW... Thanks for the above advise. And all the other advise you have given...

BB.

Re: Using PU truck to charge batteries.

By the way--sorry, I did not mean it was hard to predict... But it is hard to know without knowing the Battery AH capacity and the alternator's average output.

For charging to 80-90% maximum, with a charger and high enough voltage, you can charge the batteries pretty fast (C/20 or 5% charge rate to C/8 or 13% charge rate)...

So, knowing size of battery bank, how far discharged, and current from charger--it does become, for example:

• 210 AH * (0.80 end charge - 0.20 starting charge) / 45 Amp ave alternator output = 2.8 Hours to 80% state of charge

So--you have a choice of purchasing a $25-$30 shunt or a $100-$200 clamp on DC Amp Meter and a hydrometer (to estimate state of charge)--or just run the bank until you see some consistent bubbling.

Reality is--are you prepared to run your truck engine at high idle for 3-5 hours or so?

Or, would you be better off with a Honda eu2000i (or eu1000i) and a 40 amp (or 20 amp) AC charge controller... The Honda is probably going to be way more fuel efficient than the truck engine (1.1 gallons of fuel will run the genset for ~4-15 hours--depending on load).

-Bill

packdaddy

Re: Using PU truck to charge batteries.

I would prefer the Honda, but $1000 buys a lot of gas. And I only do this twice a year.

packdaddy

Re: Using PU truck to charge batteries.

I did find this 800 watt generator On sale locally for $100. I know it's cheap but might it get me out of a bind?

I figure it's about 7 amps. Please correct me if I'm wrong.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=66619

Renewable Ray

Re: Using PU truck to charge batteries.

I have never done this but want to be able to in a pinch at my mountain property. I like the inverter/battery charger route for sure.

Is one of my modified sine wave inverters going to be sufficient, or do I have to dedicate another pure sine wave to this project?


:roll:

BB.

Re: Using PU truck to charge batteries.

An "average" battery charger has a poor "power factor"--basically takes more current than needed (not watts, but V*A)... Assume 800 watt genset can power a 400 watt charger load:

• 400 watts * 0.8 charger eff * 1/14.5 volts charging = 22 amps into battery

I don't know if your MSW would work with your generic battery charger... Some combinations work well, others do not. You probably have an 80% that they would play together all right...

Again, unless the charge controller says it is Power Factor Corrected, assume that the MSW inverter needs to be roughly 2x the watt rating of the battery charger. You can get a Kill-a-Watt meter to double check (it measures all of the common AC values of Volts, Amps, Power Factor, VA, and kWHrs).

The big advantage to the eu2000i, besides being very quiet, is that at 400 Watts load is uses very nearly 25% of the fuel vs full load (15 hours at 400 watts vs 4 hours at 1,600 watts on 1.1 gallons of gasoline).

The standard gensets usually only run ~50% fuel flow when operating between 0-50% load--So the cheap gensets can consume 2x the fuel (or more) vs the inverter/generator style gensets (when operated at lower loads--typical for emergency and cabin loads).

-Bill

Brock

Re: Using PU truck to charge batteries.

packdaddy wrote: »

The Trailer also has a 3 stage charger tied into it's electrical.
I also have a basic cigarette lighter plug in 750 w car inverter.
A Ship to Shore 10 amp deep cycle / Marine battery charger (not 3 stage)

I would try the 750w inverter, but you would have to connect it directly to the main battery, then simply plug in your existing built in charger in the trailer and see what it does. The charger might be to big of a load, but if not your set.

The advantage of using the truck is it will be quiet, compared to a cheap genset and probably about the same fuel wise. It also won't take up any extra space and has its own built in gas tank But it is more hours on the truck engine.

packdaddy

Re: Using PU truck to charge batteries.

Thanks Brock,

I have wondered how much fuel my truck would use in idle. These portable generator claim to run 5 - 6 hours on one gallon of fuel. Would my V8 really be about the same?

My batteries are fairly low and there's not much sun today so I may just experiment with it today and hook up as you suggested.

Would a good way to test be to check the amps going into the battery inline using a multi meter?

BB.

Re: Using PU truck to charge batteries.

Most multi-meters are limited to 10 amps... A good sized truck alternator could output 70-120 amps.

Either you need a shunt or a clamp on DC amp meter for proper current measurement.

If you want to make your own shunt... Say you want to measure 100 amps and 0.1 volt drop...

• V=I*R
• R=V/I=0.1v/100v=0.001 ohms
• 14 awg copper house wiring is ~0.0025 ohms per foot at 70F
• 10 awg wire ~0.001 ohms per foot

So, get a:

• 14 awg => 0.001 ohms desired * 12 inches * 1/0.0025 ohms per ft = 4.8" copper shunt
• 10 awg => 0.001 ohms desired * 12 inches * 1/0.001 ohms per ft = 12" copper shunt

It will probably get you with in the ball park (less than a factor of 2 error) of estimating the current going into your battery bank:

• DVM reads 0.001 or 1 mV = 1 amp
• DVM reads 10 mV = 10 amps
• DVM reads 100 mV = 100 amps

Be careful, the shunts may get hot (100 amps through a 0.001 ohm wire):

• P= I^2 * R = 100a^2 * 0.001 ohms = 10 watts

You can build your own shunt based on the above... Copper is sensitive to temprature... If the wire was heated to 100C (212F)--the resistance would be ~31% higher or 0.0013 ohms.

-Bill

Brock

Re: Using PU truck to charge batteries.

What is the built in charger rated for? Is there a meter on it?

I am not sure what a V8 consumes at idle. I know at idle our small VW diesel consumes about .12 gph and our Sienna minivan consumes about .3 gph, if I had to guess maybe .5 gph?

If it matters your truck will probably burn the fuel more cleanly or environmentally friendly than a small portable genset would.

BB.

Re: Using PU truck to charge batteries.

Brock,

GPM--gallons per minute

OR

GPH--gallons per hour

I would vote for the per hour...

-Bill

packdaddy

Re: Using PU truck to charge batteries.

OK... I tried hooking up my 750 w inverter into my RV's shore line and it does not work. I have an LED night light plunged into one of 120v sockets inside and it just flashes. The clock on Micro wouldn't come on either.

Plugging my Trace inverter/charger into the 750 did not work either.

However the old ship to shore 10 amp charger plugged into the 750w car inverter is working. It's built in meter is saying 7 amps. The truck is in Idle and revving the engine does not seem to change the amp output.

packdaddy

Re: Using PU truck to charge batteries.

I found a much simpler and probably more effective way. BB Let me know what you think.

I disconnected my solar panels from the Controller and hooked my truck battery to the controller. Now my truck is acting as my solar panel / power-source.

BB.

Re: Using PU truck to charge batteries.

PD,

What type of solar charge controller (PWM or MPPT)?

In general, the charge controller needs the input voltage to be a bit higher than the battery charging voltage... So, depending on the charge controller type, your output voltage may be 0.2-1.X volts lower than your input.

That will not charge your external battery bank very well.

Just hooking the external battery bank to the truck battery with short/heavy cables is probably the best you are going to get without going into the gluing extra hardware (such as inverter and AC battery charger) to get higher charging currents to the battery bank.

The problem with 7 amps charging to your external bank is that it is not very much power... Even a "smallish" 100 AH storage battery drained to 20 AH (20% state of charge) is going to take:

• 70 AH (back to 90% state of charge) / 7 Amps = 10 hours of engine run-time (unless you discharge your starting battery--not recommended at all).

If your truck runs ~0.5 gallons per hour--that is 5 gallons of fuel to charge up the battery bank...

Put a 20-40 Amp charger on a Honda eu2000i, and the same thing (2-5 hours of charging) will take less than a 1/2 gallon of fuel (actually, maybe less than 0.2 gallons).

Note, that the 20-40 amp charge rate is very high for a 100 AH deep cycle battery... You might be able to justify hooking a 20 amp charger on to it (C/5) -- as it will probably drop back on the current unless you have the charger's voltage set really high.

If you have a larger external bank--then the higher current will be really nice (C/8 or ~13% of bank capacity is a good high end number for a generic bank).

I understand that this is a one time deal... But this is a tough issue to work around cheaply (and I like cheap ).

-Bill

PS: You will have to watch your state of charge of the truck battery... A setup with a 120 VAC inverter and external battery charger will be independent of truck RPM/alternator output--right up until you pull the truck battery down to 10.5 volts.

In reality, I am sure the alternator can keep up with a 20-30 amp draw to charge the external bank---But you want to monitor the truck battery and make sure that it does not drop below 12.8 volts or so--below that voltage, you are drawing power from the truck battery (and could run it dead in a worse case scenario).

Brock

Re: Using PU truck to charge batteries.

BB. wrote: »

Brock,

GPM--gallons per minute

OR

GPH--gallons per hour

I would vote for the per hour...

-Bill

DOH, yes GPH, I will go fix it...

packdaddy

Re: Using PU truck to charge batteries.

I'm not opposed to buying a new plug-in charger as long as I don't have to buy a new inverter. My current plug-in is old and has limited functions. It's time to upgrade anyways.

I found a decent B&D charger that has several settings 4/10/20/40/110 AMP. It is also supposed to recondition old sulfated batteries.

The manual doesn't indicate watt usage so I'm not sure if my 750w inverter will power it or if it depends on the setting.

http://www.lamabrewery.com/camping/VEC1093DBD.pdf

Brock

Re: Using PU truck to charge batteries.

Any idea how big the built in charger is? I really would have thought the 750w inverter would have powered it. When you had it feeding your shore power was everything else off? If there were some larger load trying to start, like a refrigerator or heater of some sort that would cause the inverter to flash your led night light as the inverter kept trying to restart. Although maybe the built in charger is too big for the 750w inverter which would to the same thing.

packdaddy

Re: Using PU truck to charge batteries.

I was able to connect my trace 1500 watt inverter to my truck and hook up a Die Hard 2/12/30/80 amp charger (on sale now at Sears $50) and charge at 30 amps. It works great and also runs my trailer with no problem. I had to increase my wire size as they were getting a bit warm.

thanks for the help!

Brock

Re: Using PU truck to charge batteries.

yaaa, did you try the trace feeing the trailer? Although it sounds like you have it figured out.

niel

Re: Using PU truck to charge batteries.

packdaddy,
i've been wondering of some of those battery chargers as the voltage requirements for batteries to switch stages can vary widely. do they make a provision for this variability or is it a one size fits all type of a deal with only 1 set of preset voltage setpoints? if the voltage setpoints are not good for a certain battery is it possible to run the charger manually rather than automatically? literature for many of these chargers give so little information and if you are aware of that particular charger's voltage setpoints i'd like to hear what they are. ie bulk and float voltage setpoints.

packdaddy

Re: Using PU truck to charge batteries.

Yes the trace runs the trailer fine. I can even use the microwave.

As far as the set points for this charger. I don't think this one is that smart. It's not exactly a three stage automatic charger. The only thing automatic about it is, it will stop charging so your battery does not overcharge.

I manually put it on 30 amps and it charged until it got to 14.5 volts and showed 100% then it switched to trickle or stopped charging, I'm not sure but I could still hear the fan. I will see if I can upload the manual and you can check it out.

My trace inverter also has a nice three stage built in charger and is customizable to your battery bank. But will only charge off of AC 110v Power.