Troubleshooting Alternator Charging

Fester55 · Veteran Member

Troubleshooting Alternator Charging

rgren2 · Guru

Isolate each battery and measure the voltage of each one. You will then know the culprit.

Dick0 · Guru

Are you charging the house batteries through a VSR or DC > DC charger?

Is the charging cable from the starter battery wired through a relay and/or reset fuse?

Check those components now seeing that the house batteries read 12.6V.

Charge the house batteries with a 240V battery charger and take a reading of the rested batteries voltage.

TimTim · Guru

You have had a system that has worked for years.

As rgren2 said isolate each battery and test. Also charge each battery seperately and run a decent load like a compressor on them whilst measuring the voltage at the terminals.

Jaahn · Guru

Fester55 wrote:
I bought my Ford Transit motor home six years ago and never had any troubles charging while driving. Recently I noticed that the house batteries weren't charging anymore.Used my multimeter to test across the terminals of my starter battery with engine running and I read 14.2-14.4V which is normal.I have 3x 6 year old Ryktar 120Ah batteries and the reading was around 12.6V. Disconnected all the batteries and test results where around 12.6V for each one. Disconnected the charging cable from the house batteries. I was expecting 14.4V but the reading is now 3.0VThe diameter of the cable is 10mm including insulation. Can't measure the copper itself. Length of cable is roughly 4-5 meters. Not sure if voltage drop might be the culprit.
Only variable is that new batteries were installed a few weeks ago but I doubt that it would be the issue. Has worked fine for 6 years so I'm stumped on this one.
Charging works fine with both 240V and solar controller. Hopefully one of you folk might shine a light on this. Cheers.

Hi Fester as an experienced trouble shooter I would be looking at the installation of your new batteries. If they were working for 6 years and you had someone do work and they are not working correctly now why would you say "i doubt that would be the issue" ??

Get it checked !

Jaahn

-- Edited by Jaahn on Thursday 18th of April 2024 10:18:08 AM

Greg 1 · Guru

X2 with Jaahn

Fester55 · Veteran Member

After crawling underneath I found this box halfway between the batteries. No idea what it is inside.

Just hoping that it's something inside the box that's failed.

Thanks for your help. Off to see an auto electrician soon.

As soon the issue is resolved I'll update the post.

Cheers

TimTim · Guru

Hi Fester55,

My apologies as I did not read your original post correctly and so did not pick up on that you have new batteries and that they charge ok. A combination of a late night and some alcohol to take way some pain blankstare .

As you have said the only thing you have changed is your batteries and being a drop in replacement you would expect the ssystem to work. You havent stated the make and model of your DC to DC charger but my thoughts are that your DC to DC charger is acting just like a solar controller when connected up in the incorrect order.

Try this before seeing your Auto electrician. Disconnect your DC to DC charger from the vehicle input and from your battery bank. Connect it up to your battery bank first so that it can read the battery voltage and check any settings as per the manual. Then connect it to the vehicle battery.

Can you post the make and model of your DC to DC charger.

Good luck

Tim

rgren2 · Guru

The box looks like a voltage dependent relay.

Fester55 · Veteran Member

Tim, the vehicle doesn't have a dc-dc charger installed. The box in the above photos is the only connection between starter and house batteries that I can see.

As per the diagram I first disconnected the cable at the starter battery end and the reading was 12.6v. Connected again and disconnected at the house battery end. Result this time was 0v.

Never heard of a voltage dependent relay so I'm assuming something in there is now stopping the current from getting through.

Cheers.

Dick0 · Guru

What's the importance of the starter?

The alternator is the source of charging.

rgren2 · Guru

VDR is used in two battery systems, it allows the secondary battery to be charged off the main system, but when the main system is not charging, the secondary battery will not discharge the primary battery. VDRs are usually set at 13.2-4V. There are many types, some are actual relays and others are electronic gizmos. On the caravan they allow you to use your electronics in the caravan when connected to your tow vehicle without draining the vehicle start battery when the engine is turned off, but when the engine is running it allows the caravan batteries to charge via the vehicle alternator. On some modern vehicles the smart alternator may need to be modified slightly so it can charge the caravan batteries and not throw a code in the vehicle.

Dick0 · Guru

rgren2 wrote:
VDR is used in two battery systems, it allows the secondary battery to be charged off the main system, but when the main system is not charging, the secondary battery will not discharge the primary battery. VDRs are usually set at 13.2-4V. There are many types, some are actual relays and others are electronic gizmos. On the caravan they allow you to use your electronics in the caravan when connected to your tow vehicle without draining the vehicle start battery when the engine is turned off, but when the engine is running it allows the caravan batteries to charge via the vehicle alternator. On some modern vehicles the smart alternator may need to be modified slightly so it can charge the caravan batteries and not throw a code in the vehicle.

Are you referring to dual VSR's (Voltage Sensitive Relay)?