Second battery not charging properly

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Ryperd
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Second battery not charging properly

Post by Ryperd »

A good friend gave me his old Waeco CF-18 fridge/freezer when he upgraded. I already had the wiring for dual batteries, but had never had the equipment to make use of it. There was an old marine switch connecting the two batteries, but it was dead, so Louis from 4x4megaworld helped me to swap it out for a solenoid that closes the circuit to the second battery when the ignition is on. The second battery is connected in the load area, with thick cables running from the front to the back. In the front I have a regular 62Ah battery, and at the back is a 50Ah deep cycle battery.

I recently spent a week or so camping in Kruger, so I had a chance to test out the setup. The system worked great when I was in an electrified camp and I could attach a charger to the second battery overnight (I have a Stanley 7A charger). But as soon as I was staying in a bush camp without electricity and was just charging from the alternator, the batteries seemed to end up with less charge after 6 hours of driving than they had first thing in the morning. In the end we had to unplug the fridge to keep the batteries alive.

After a day of driving (probably about 7 hours) with the Waeco set to a fridge temperature, I took the following voltage readings on the two batteries (unfortunately I didn't take any measurements at the start of the day to compare, but the fridge was off overnight).

With the car off:
Front battery (rear disconnected): 12.51 V
Front battery (rear connected): 12.38 V
Rear battery (fridge disconnected): 12.37 V
Rear battery (fridge connected): 12.26 V <- battery protector preventing the compressor from kicking in

With the car on:
Front battery (rear disconnected): 13.10 V
Front battery (rear connected, fridge connected): 12.81 V
Front battery (rear connected, fridge disconnected): 13.00 V
Rear battery (fridge disconnected): 12.98 V
Rear battery (fridge connected): 12.83 V

There are many possible issues here, and I'm not sure how to figure out which it is:
1) The alternator may need to be replaced / upgraded. It worked fine when there was only one battery, but maybe it can't handle two batteries + fridge.
2) There could be a problem with one of the batteries - probably the deep cycle, which is relatively old. I know the capacity should be higher, but that shouldn't result in a charging problem when the alternator is running?
3) Maybe I need a DC-DC charger to step up the voltage at the back? I don't know enough about these to know whether it's necessary or not.
4) Something else?

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Re: Second battery not charging properly

Post by Obelix and Dogmatix »

Hi Rudi

Have you checked the voltage regulator on your altenator as you should be getting 14V + at your batteries.

If you remove the second battery from the vehicle and just charge it with you stanley 7 amp battery charger, what does the voltage measure when fully charged?

It could also be that your altenator is a bit small.

By the way what vehicle do you drive then maybe someone with a similar vehicle could do some comparative measurements for you.

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Re: Second battery not charging properly

Post by Ryperd »

Thanks Quentin. I'll charge it overnight and check the reading. I think it was just over 13 V, but I can't remember the exact voltage. The vehicle is a '94 4Y SFA.
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Re: Second battery not charging properly

Post by WayneSchalk »

Hi Rudi, somewhere on the forum is a very informative thread, I just always battle to get it. Electricery for camping..... someting like that. Ill post the link as soon as I get it, have a read through it, you might just pickup what your problem is there.

Just a note, 50ahr deep cycle is rather small, most commonly you will see they guys use 102ahr deep cycle, AND with a DC-DC charger, the solenoid setup on the alternator does not charge a deep cycle back to the full capacity.
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Re: Second battery not charging properly

Post by CasKru »

Your front battery should read an absolute minimum of 13.6v when car is idling.
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Re: Second battery not charging properly

Post by LouisZ »

Let them test the batteries. You mention they old, if that is the case they wont hold charge long especially under load.
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Re: Second battery not charging properly

Post by Ryperd »

WayneSchalk wrote:Hi Rudi, somewhere on the forum is a very informative thread, I just always battle to get it. Electricery for camping..... someting like that.
Thanks Wayne. Is this the one?
WayneSchalk wrote:Just a note, 50ahr deep cycle is rather small, most commonly you will see they guys use 102ahr deep cycle, AND with a DC-DC charger, the solenoid setup on the alternator does not charge a deep cycle back to the full capacity.
Yes, it looks like I'll have to get a DC-DC charger for anything longer than a weekend trip (looks like I got my timing right with Cassie's Garage Sale!). But still, there must be something else wrong here if it can't even maintain its charge.
CasKru wrote:Your front battery should read an absolute minimum of 13.6v when car is idling.
Thanks Cassie. I'll test it again now with a full battery and see whether it gives a different reading.
4x4megaworldpta wrote:Let them test the batteries. You mention they old, if that is the case they wont hold charge long especially under load.
Good point, Louis. I'll go get both tested, then at least we can work out whether the batteries are part of the problem or not.
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Re: Second battery not charging properly

Post by WayneSchalk »

Ryperd wrote:
WayneSchalk wrote:Hi Rudi, somewhere on the forum is a very informative thread, I just always battle to get it. Electricery for camping..... someting like that.
Thanks Wayne. Is this the one?
That's the one....
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Re: Second battery not charging properly

Post by ChrisF »

Rudi appart from the need for a dc-2-dc charger it sounds like you have an old battery there thats seen better days ....


My deep cycle is now also at that point where it is overdue for replacement ... just waiting for the next trip before I do replace it. Charge as a I may, after a few hours off the charger the volts drop to 12,7V, then 12,4V the next day. Still okay for another weekend trip or two, but WILL replace it before I head off toward Namibia again.
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Re: Second battery not charging properly

Post by Ryperd »

Okay, I had both batteries tested, and both passed (they should at least maintain a charge). I'll charge the deep cycle overnight and check the charge in the morning (after an hour or so off the charger), and again in the evening. I know I can do with a bigger, newer deep cycle, but it seems I'd be better off putting that money towards a dc-to-dc charger for now.

I checked the battery voltage again with the alternator running, and it came out at 13.2 V while idling, so it seems the alternator does need some attention. What would be the next step? Take out the voltage regulator and have it tested by an auto-electrical place? Or should I just take the bakkie in and have them check out the whole setup?
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Re: Second battery not charging properly

Post by ChrisF »

Rudi even if they work on the alternator they will only lift the voltage "a bit" .... an alternator was never meant to deliver 14,5V to fully charge a deep cycle battery.
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Re: Second battery not charging properly

Post by Ryperd »

ChrisF wrote:Rudi even if they work on the alternator they will only lift the voltage "a bit" .... an alternator was never meant to deliver 14,5V to fully charge a deep cycle battery.
Yes, it's clear that I'll need to get at least a DC-to-DC charger to step up the voltage to the deep cycle at the back. I've put my name down for the 30A charger that Cassie is selling. The question is whether I'll also need to have some work done on the alternator / voltage regulator to lift the voltage that little bit, or whether the DC-to-DC charger is all that I need.
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Re: Second battery not charging properly

Post by Family_Dog »

Not necessary, The 30A DC Charger from Cassie can be set to charge at a higher voltage than the primary battery, refer the DIP switches on the unit. Just ensure the DC-DC charger is mounted close (within 500mm) of the rear battery, ensure you have adequate wiring from the alternator to the charger and charger to battery. Fuse the charger supply line as close as possible to its source of power. The brown wire on that charger should be connected to the ignition switch or any supply point that only has power when the ignition is on, this would control the DC-DC charger and ensure that it only has power when the engine is running.


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Re: Second battery not charging properly

Post by legend35 »

A dc to dc is all you need for the second battery.Just buy a new regulator for the alt,it will be cheaper .Auto electricians are very expensive.You need 13.8V for the front battery.
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Re: Second battery not charging properly

Post by Johan Kriel »

Dump the weaco, and buy something else. :lol: Check what amps it draw.

Friend having the same problem except he has 2 aux batteries, a weaco and a engel. If the weaco is disconnected everything is fine, but with the weaco the aux batteries are not fully charged. He has a 90 amp alternator in the car and seems to be working fine, but we had not a way in the veld to check what amps it put out.
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Re: Second battery not charging properly

Post by Family_Dog »

Yes, but you need 14.1 - 14.4v for the rear battery and there will be anything from .1v - .2v voltage drop along the way.

Forgot to mention that with Cassie's DC-DC charger, you would remove the CH relay, no longer necessary.

Your VR could be a bit tired as well regarding the front battery, which should initially charge at 13.6/13.8v or so then drop a bit depending on the state of charge of the battery within about 10 minutes or so, as the battery nears full charge.


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Re: Second battery not charging properly

Post by LouisZ »

Go for the DC-DC charger.
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Re: Second battery not charging properly

Post by Ryperd »

Thanks for all the advice! I'll put in the DC-DC charger and replace the voltage regulator myself. Unfortunately this will mean I have to go on another weekend trip to test it! :siffler:
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Re: Second battery not charging properly

Post by ChrisF »

leave the VR .... more money for beverages for the test weekend .... :twisted: :lmao:




jokes aside - the alternator voltage needs to go high enough to START the dc-2-dc charger !!
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Re: Second battery not charging properly

Post by george »

Have you tested your voltage at the main battery with the 2 second batteries disconnected?
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Re: Second battery not charging properly

Post by Ryperd »

george wrote:Have you tested your voltage at the main battery with the 2 second batteries disconnected?
Yes, the 13.2 V reading is with primary battery only.

Also, I charged up the deep cycle last night to test its ability to hold a charge. Immediately after charging it was at 13.14 V, but I think that's surface charge. After about half an hour it had dropped to 12.98, but today it's holding steady at 12.8 V. So I think it should be in good enough condition that it wouldn't put a drain on the whole system.
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Re: Second battery not charging properly

Post by Ryperd »

ChrisF wrote:leave the VR .... more money for beverages for the test weekend .... :twisted: :lmao:
I like the way you think Chris!
ChrisF wrote:jokes aside - the alternator voltage needs to go high enough to START the dc-2-dc charger !!
With the car on, it was already seeing 12.98 V. If that's not enough, I have my questions about the dc-2-dc charger!

All that I've measured here is volts though, so should I be concerned that there are maybe not enough amps reaching the back of the bakkie (or the front for that matter)? Or if the voltage is in the correct range is that good enough?
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Re: Second battery not charging properly

Post by LouisZ »

Volts too low. Get the Bosch Regulator, it be marked 14V and should give 13.7 up on the SFA. Also check the connections to the Altinator. Sometimes the wire that runs from the battery to the Alt gets old and this cause resistance, then you sit with not enough volts&amps to your battery.
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Re: Second battery not charging properly

Post by ChrisF »

Rudi please just check the specs of the dc-2-dc you want to buy ....


for some reason I have a figure of 13,2V in the back of my mind, the alternator to reach this volts before the dc-2-dc will start up ....


also just blip the throttle when you check the alternator voltage, sometimes it wants a bit of revs to actually get going. A healthy alternator really should have an output voltage of over 13,5V, normally closer to 13,8V.
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Re: Second battery not charging properly

Post by Ryperd »

ChrisF wrote:Rudi please just check the specs of the dc-2-dc you want to buy ....

for some reason I have a figure of 13,2V in the back of my mind, the alternator to reach this volts before the dc-2-dc will start up ....
I think it's this charger, Chris: viewtopic.php?t=28855

Seems it should work with anything upwards of 9.6 V
ChrisF wrote:also just blip the throttle when you check the alternator voltage, sometimes it wants a bit of revs to actually get going. A healthy alternator really should have an output voltage of over 13,5V, normally closer to 13,8V.
Just tested it again and now it was giving 13.47 V without any throttle action :think:. I think I'd rather have a bad reading than an inconsistent reading. Is there some way to test what amps it's pushing out without a putting one of those fancy volt and amp meters in the circuit?
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Re: Second battery not charging properly

Post by ChrisF »

Rudi do remember an alternator works while you are driving - thus significantly above idling revs .... anything over 1500 rpm should give you a good indication of what happens while you are driving.


DC amps is a bummer to test .... either the whole shunt setup, or a R 1500 dc clip on amm meter.
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