Charge RV batteries from Tow vehicle alternator....?

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  #1  
Old 04-09-15, 10:23 PM
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Charge RV batteries from Tow vehicle alternator....?

Well I was told I shouldnt do this after the fact I already did it...LOL.

This may be a long read but it may interest some and may help others...

Maybe this should go in camping section but I figure this is a better spot..

So dry camping in the local state forests here in NJ I did not want a loud generator. Also I dont have a smart charger in my 2003 camper. I have two batterys and want to charge them at 14 volts quickly and came up with this. It works well but many are telling me I will melt/ blow up/ explode my alternator... I dont see it but maybe time will tell.

Here is what I did. I took 6 gauge wire to minimize voltage drop. These have Anderson style plugs on the end. I had to solder some new rings on and such. Also added 50 amp resettable breakers. One on truck side and one on RV side.

RV battery's are 75 AH for 150 ah total. With 50% draw down I would need to put back this 75 ah in the shortest time.. I feel I got a decent charge in a few hours. Oh some said I will kill my truck idling it that oil will not flow properly... Its amazing the story's I have been told so far...

Here are the pics and my test reading. I tested amps, volts, and alternator temps every 20 minutes. I did a full 4 hour test...

6 gauge wire with Anderson plugs

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50 amp breakers

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RV wired with breaker. 8 ft lead rolls up nice and fits in box.

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truck side battery with breaker. Note this is a cs130D 105 amp alternator.

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Hooked up

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And here are the readings I got..


I drained camper battery's down to 12.3 volts

The test below is 20 minute intervals..... 130d alternator 105 amp .... Chevy 1996 s 10.

5pm start

amps 57
volts at camper battery's 13.99
alt temp 148f


5:20

amps 22.4
volts at camper batterys 13.93
alt temp 188f

5:40

amps 19.5
volts at camper batterys 14.05
alt temp 187f

6:00

amps 13.4
volts at camper batterys 14.02
alt temp 176f

6:20

amps 11.3
volts at camper batterys 14.09
alt temp 171f


6:40

amps 8
volts at camper batterys 14.20
alt temp 159f

7:00

amps 5.8
volts at camper batterys 14.22
alt temp 160f

7:20

amps 4.9
volts at camper batterys 14.33
alt temp 155f

7:40

amps 4
volts at camper batterys 14.34
alt temp 154f


Note: I could have probably stopped here as batterys were most likely charged.

8:00

amps 3.2
volts at camper batterys 14.34
alt temp 154f

9:00

amps 2.7
volts at camper batterys 14.39
alt temp 154f

9:10

After running the furnace for 10 minutes to take off the surface charge, I took a final volt reading.

12.85 volts at battery.

In summary without using amp meter or anything else when camping I will charge until volts get up to the 14.3 mark and stop there more or less... This will be with my volt meter I have in the camper..

Although I always carry my multimeter with me and the hydrometer...

An actual alternator person on line actually told be I should test the temp at the diodes of alt and not the windings as I did..

With that said does anyone have advice or feed back for me?
 

Last edited by lawrosa; 07-27-15 at 08:07 AM.
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  #2  
Old 04-09-15, 10:31 PM
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And here I made a volt meter for the camper from a wall plate and a $10 meter and switch I got off amazon. I calibrated it to read what the batterys read. This is because I hooked it to 12v wires in the wall that go to the monitor panel..

Wonder if there is an interest in these in the RV market??? LOL..

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  #3  
Old 04-09-15, 11:05 PM
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It's definitely going to shorten the life of your alternator some. It'll cost you a little more in gas to charge then to use a generator. No biggie.

Maybe consider some solar power here too.


Mike.... I've got to tell you.... these new little gennys by Honda and Yamaha are whisper quiet.
I've got a Honda 1k and you can't hear that thing from a couple of feet away.
 
  #4  
Old 04-09-15, 11:30 PM
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It's definitely going to shorten the life of your alternator some. It'll cost you a little more in gas to charge then to use a generator. No biggie.
.3 gph idling Total $ 3 in fuel.


I figure whats the difference from what I am doing compared if a car has heated seats and hi power options, its raining, night time headlights and wipers on, defogger and blower on..

How many amps is that car using... Oh stuck in traffic on the Connecticut thruway?

My truck has no options but was fitted with a 105 amp alt. I could go to an AD244 alt GM makes direct fit @ 145 amps...

Maybe consider some solar power here too.
Solar dont work in the woods ..And too much $$$$ My set up cost $50.....

Mike.... I've got to tell you.... these new little gennys by Honda and Yamaha are whisper quiet.
I've got a Honda 1k and you can't hear that thing from a couple of feet away.
At what price? I thought of it but how do I charge the RV batterys with a gen? If I plug in my camper my onboard convertor is linear and charges at 12 amps max and 13.6 volts set voltage... It would take days to charge the batterys...

Im looking for a better way but have not found it...


Yes I can nix the batterys somewhat and run a gen all day and night for power but im in pristine wilderness/forest. I want to hear the babbling brook, birds....etc..


http://www.state.nj.us/dep/parksandf...amily_camp.pdf
 
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Old 04-10-15, 12:12 AM
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I want to hear the babbling
That you can hear here.

Your battery system looks good. Should work fine in your application.
 
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Old 04-10-15, 07:58 AM
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I think it looks pretty good to me. Do you plan to charge while you're towing to the camp site or just sitting at idle?
 
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Old 04-10-15, 11:43 AM
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Looks good to me. I was thinking gas or diesel truck, the diesel would be more efficient at idle. Then again, there are about a million cop cars idling a lot...

I'm not all all worried about the alternator. They have fans for cooling. And, as you can see, you are really are not pulling more than 1/2 of its rating.

Max rated Diode CASE temp. is 200 deg C. Die temp closer to 250 C!
 
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Old 04-10-15, 08:28 PM
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I think it looks pretty good to me. Do you plan to charge while you're towing to the camp site or just sitting at idle?
Just sitting idle....why???
 
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Old 04-10-15, 08:55 PM
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Thats in C but someone did state test at diodes and not windings at F temps... Diodes should not be more then 250F I was told..............
 
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Old 04-13-15, 09:27 AM
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Oh I was just curious -- seems like either way could work if you ran the cables back to the rear bumper.
 
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Old 04-15-15, 04:43 PM
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Years ago in the UK the lights were gas and the fridge gas was lit with built in flint and the water pump had the option of being foot operated. At that time using split charging diodes was really a flop but using the split charging relay worked well. The whole idea of the relay is two fold one you can't discharge tow vehicle battery when parked but second more important was the vehicle starter would not draw power from the caravan.

At first we would connect the relay coil to the alternator warning light and with fords we could use the ignition switch aux but as time went on the alternators become more complex and we started using a voltage trigger for the relay.

However as we started to use more power the 5 amp typical charge while towing was not enough so the second battery was moved to the car and we had three batteries the car own never touched, and the cars second one in a plastic bread bin so no acid could spill and tied down would be swapped with the caravan one.

Stripping the Lucas alternator we could squeeze in an extra three diodes so alternator had two outputs but as we went to Japanese cars this stopped.

Today those who still want to split charge use inverters the technology has moved on. Designed really to charge the battery for the bow thruster on narrow boats two UK firms make battery to battery chargers using three stage charging so from flat it charges a 12 volt battery at max amps often around 25A depending on model and once battery voltage get to 14.4 or 14.8 depending on battery type it holds it at that voltage until the current drops to around 5A when it reduces voltage to 13.4 volt. Some examples here Battery to Battery Chargers | Sterling Power Products. However they are not cheap.

With narrow boats drawing 180A from two engine alternators is not unusual but with the car we tend to only have one alternator. In the main I have not had a problem drawing the extra current except with some French cars which had single phase alternators with just 3 diodes. These would over heat even if all you did was fit a bigger battery. In the main alternators are self regulating for current output. There are exceptions the CAV AC208 alternator used on British buses had a special RB440 regulator with M1 and M2 terminals which went to a resistor to measure current these alternators could give out 60A at tick over and were specially designed for buses.

USA gear also had some odd alternators Grove cranes had alternators with 12 and 24 volt outputs the latter from a built in three phase transformer. Plus they were brushless.

Today we are starting to see a new type of alternator linked to the engine management which switches off the alternator when you want more engine power and charges in the main when engine is on over run. These are a real problem with split charging as you can easy flatten the battery even with engine running.

So slowly split charging is going and is being replaced with solar panels and wind chargers. But in the UK it is quite a small island and camping sites need a licence so slowly all caravan sites are getting mains huck up points. Soon there will be no need for split charging or inverter generators as mains is provided on the sites.

Clearly with such wide open spaces it is going to be very different in the USA. But likely what we use on narrow boats you can use on caravans. Our caravans can't weigh over 30 cwt as that is the limit on a 50mm ball once you go over 1.5 ton then you have to fit all sorts like special brakes and so it's very rare for a caravan to exceed 1.5 ton which limits what they carry. But the narrow boat is often 20 ton with loads of ballast so weight of batteries is not a problem having 500 Ah of batteries is not unusual.
 
  #12  
Old 04-15-15, 06:19 PM
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Today we are starting to see a new type of alternator linked to the engine management which switches off the alternator when you want more engine power and charges in the main when engine is on over run. These are a real problem with split charging as you can easy flatten the battery even with engine running.
Yes as I have researched that the new alts reduce volts to 13.6 volts for fuel savings...etc..This is on new vehicles.. I have come to find out an additional feature of tow/haul mode on vehicles switches this computer controlled feature off. Aside from shift points..

So when towing always use the tow/haul mode for this one reason alone.

Today those who still want to split charge use inverters the technology has moved on. Designed really to charge the battery for the bow thruster on narrow boats two UK firms make battery to battery chargers using three stage charging so from flat it charges a 12 volt battery at max amps often around 25A depending on model and once battery voltage get to 14.4 or 14.8 depending on battery type it holds it at that voltage until the current drops to around 5A when it reduces voltage to 13.4 volt.
I know the dc to dc smart chargers are the way to go but the price put me off.

What I have found in the past couple days is the quicktifier.. Basically an external rectifier. Taps right from the alt...

This will be my next mod I think. At $109 bucks seems worth it to me...

But then again my alt has not died from heat as of yet...

This link and video are for reference only..

http://alternatorparts.com/quicktifi...rectifier.html

https://www.youtube.com/watch?v=3o_cWxAsyDI
 

Last edited by lawrosa; 04-15-15 at 08:39 PM.
  #13  
Old 04-15-15, 07:58 PM
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Mike, I'd do that the others said and get a small inverter generator. You can get chargers for your RV rated at least 50A off the top of my head, probably more. If you really wanted to get crafty you could probably put a truck alternator on a small engine and charge your batteries that way, too.
 
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Old 04-15-15, 08:43 PM
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Mike, I'd do that the others said and get a small inverter generator. You can get chargers for your RV rated at least 50A off the top of my head, probably more. If you really wanted to get crafty you could probably put a truck alternator on a small engine and charge your batteries that way, too.
Yes that is correct I can get a small gen...But why would I want to spend 1000 bucks??

Yes I can get a new convertor charger and spend about 200 bucks. Now I am into it for 1200 bucks..

Why do I want to do that opposed to what I am doing?

If you really wanted to get crafty you could probably put a truck alternator on a small engine and charge your batteries that way, too.
LOL.. Okay why would I do that too? I have a 4,3liter V6 that spins the alternator just fine..

Ummm I dont get it... Is my set up not normal for some reason?
 
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