Charge rate for domestic batteries

[Archiesgrandad]

We have a Rimor Sailor 745 on the Mercedes chassis, and last year I up-graded the batteries by fitting 2 x 130 amp heavy duty traction batteries.

When the van is not in use I keep an eye on the state of charge and connect to the mains for a top up every couple of weeks, leaving them on charge for two or three days.

We have been away for the past week, and were desperately short of electricity for the duration, no hookup available. I checked the readouts from the van's control panel with my multimeter and they seem fairly accurate, and even after a three hour drive we had only 12.3 volts, the reading was taken acouple of hours after we parked up.

Now we are home I have connected to the mains and the batteries are showing 13.8 volts, and the charge was around 8 amps to start with, but after 24 hours the charge rate is down to 1.60 amps, and the readout says we have only put around 80 amps into the batteries in 24 hours. It will take days to bring the batteries up to full charge, if ever, so, is this normal or is there anything we can do to improve it?

Your help will be appreciated.

 

AGD

[Archiesgrandad]

Thanks guys.

AGD

[Dave Newell]

Voltage readings alone are not a particularly accurate way of measuring a battery's state of charge and when the charger is actually running you are reading the output voltage of the charger rather than the battery voltage. How long it will take to recharge the batteries depends on two things in general, how discharged they are and the charge rate of the charger. With 260AH of capacity to start with, if they were for example 50% charged then you need to put back 130AH of charge. At 8 amps continuous charge it will take about 16 hours to recharge them. The reality though is more than that because your charger is almost certainly intended more as a PSU (indicated by the 13.8 volt reading) than a charger and its current output will drop off as the batteries gain charge. To fully charge your batteries you need a three (or more) stage charger like a CTEK XS7000 for example which will charge them fully but will still take time as it has a max charge rate of 7 amps. If you need faster charging then the CTEK XS2500 will charge at 25 amps but it carries a hefty price tag.

 

D.

[enodreven]

Hi,

 

If you are looking for another charger these may be worth a look and at a very good price at the moment.

 

http://www.argos.co.uk/static/Product/partNumber/0383057/c_1/1|category_root|Garden+and+DIY|14418702/c_2/3|cat_15701062|Clearance+Garden+and+DIY|14519703.htm?_$ja=tsid:11527|cc:|prd:0383057|cat:garden+%26+diy+%3E+clearance+garden+and+diy

 

 

[Brian Kirby]

Archiesgrandad - 2010-08-01 11:26 PM We have a Rimor Sailor 745 on the Mercedes chassis, and last year I up-graded the batteries by fitting 2 x 130 amp heavy duty traction batteries.

I assume this was because you found the original battery was inadequate?  Can you say roughly what capacity the original was, how many Ah you use per day, and how many days you expect to survive off hook-up?

When the van is not in use I keep an eye on the state of charge and connect to the mains for a top up every couple of weeks, leaving them on charge for two or three days. We have been away for the past week, and were desperately short of electricity for the duration, no hookup available.

You say short for the duration.  I assume this means the batteries were below full charge when you arrived, despite having been on charge before you left + 3 hrs driving?

I checked the readouts from the van's control panel with my multimeter and they seem fairly accurate, and even after a three hour drive we had only 12.3 volts, the reading was taken acouple of hours after we parked up.

This 12.3 volts is the indicated figure on load, or off load?  If off load, it indicates batteries approximately 60% discharged, in other words with all useful capacity used.  Beyond about 60% discharge you are into injury time!  If on load the figure is to all intents and purposes useless, because voltage falls as load increases.

Now we are home I have connected to the mains and the batteries are showing 13.8 volts, and the charge was around 8 amps to start with, but after 24 hours the charge rate is down to 1.60 amps, and the readout says we have only put around 80 amps into the batteries in 24 hours. ............. AGD

As Dave says, if you are taking the readings with mains connected, you are probably reading the charger output.  What is the stated charge rate of the charger/power pack, and what type is it?  How much charge you will get from the alternator while driving will depend on the output from the alternator and what else you are asking it to do.  However, it will be very unlikely to recharge a heavily discharged 260Ah of batteries in 3 hours.  Using a mains charger or power pack, you should be somewhere near fully charged after 24 hours if the charger output is sufficient for the 260Ah, which I rather doubt.  However, I think you should be further up the tree than you seem to be.

Some checks are required, but it sounds a little to me as though the full charge is not reaching the batteries, neither from the alternator nor the charger.  In view of your first comment above, I just wonder if it ever has, hence my questions about the original battery and your pattern of use.  Checking all the connectors, local wiring, and fuse condition at the batteries would be a good start.  Then work back along the wiring looking for any sign of trouble, and checking all cables are of adequate size.  If that all checks OK, I would then get the batteries properly tested, since a duff cell in one will affect the performance of both.  Only after all wiring is proved fault free, and the batteries pass test, would I turn to upping the charger capacity.