Battery down

MOJO said:
Another problem. On mains since Sept but our Hymer engine battery shows flat on the control panel though its supposed to receive a charge from mains. I have not started the engine since Sept on advice its better not to protect exhaust system as can not drive it anywhere to get high enough temperatures. Leisure battery is fully charged.
No alarm on so what could have been drawing from the battery is anyone's guess.
I will have to remove and trickle charge for when it will be needed April/May hopefully. That will be eight months not running the engine! Any thoughts on the reason?
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We also have a Hymer. When picked-up and inspected I noticed that the radio was wired to the starter battery. While the radio is used when driving, it is used more when the engine is not running and was draining the battery. The 0.1A charge from the EBL was not enough to maintain the starter battery.
Besides the problem of flattening the battery, a starter battery is not designed to supply a constant current over a long period of time. A starter battery is designed to provide a very high cranking current over a short period of time, whereas the habitation batteries are designed for a low constant current but can't deliver a high cranking current needed for starting. Also. it is too simple to state that a low temperature will cause a battery to go flat faster than a warm battery. This article is interesting, ...https://www.thoughtco.com/why-batteries-discharge-quickly-cold-weather-607889
I have run a wire from the habitation batteries to the radio removing the drain on the starter battery. Asking people about this, it appears that Hymer run electrical items from the starter battery as standard fitment. In my opinion, a stupid idea!
 
i start my engin at least once a month , run it till engin heat has pickted up. i turn it round. do the checks. tyres and such. p.s. read to go. oh its not taxed.ok.pj.
ps see if it starts.happy new year
 
Update. Checked all fuses yesterday. All OK but it began to charge again. I assume a poor connection through cold or damp. Next job will be to see if it holds the charge.
IMG_20210124_150514.jpg
 
Thumbs up for the radio wired in to the leisure battery system. Our 1990 Hymer b544 had already had the original cab radio removed so I bought a bog standard radio/cd player and asked an auto electrician to wire it in to the rear . On investigation there was already a cut out in the kitchen area to take a radio with all the wires already in to connect up the radio to LB. Two nice new speakers in to replace the vintage ones and bobs your uncle. Only took electrician 30 mins start to finish. I assumed afterwards that this was the standard way to wire in a motorhome radio. With a 30 year old vehicle it wasn’t exactly high tech. Seems the obvious way to do it in retrospect
 
ricc said:
my lidle smart charger has a cut off voltage where it wont charge a properly flat battery..... have to put the old school charger on with the needle vibrating against the 4 amp stop for an hour or so to bring the voltage up then put the smart on overnight.
not sure what the cut off voltage is but it wont play with a battery down to 10 volts
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If its down that low its giggered.
 
stirlingb said:
Thumbs up for the radio wired in to the leisure battery system. Our 1990 Hymer b544 had already had the original cab radio removed so I bought a bog standard radio/cd player and asked an auto electrician to wire it in to the rear . On investigation there was already a cut out in the kitchen area to take a radio with all the wires already in to connect up the radio to LB. Two nice new speakers in to replace the vintage ones and bobs your uncle. Only took electrician 30 mins start to finish. I assumed afterwards that this was the standard way to wire in a motorhome radio. With a 30 year old vehicle it wasn’t exactly high tech. Seems the obvious way to do it in retrospect
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Cd radios went out with nelsons eye, there usb these days.
van radio.png
car radio.png
 
I’ll second earlier recommendations. Vehicles really don’t fair well being laid up. If you really are unable to take it for a 20 min drive every month then at least get the engine warm, a/c on, and drive it backwards and forwards a few yards, careful not to leave it in exactly the same spot (avoids flat spots on tyres, assuming you’re leaving wheels on). If you canpark it with the handbrake off.
If you’re minded to buy a new battery fix the EHU charging first so you don’t end up flattening it and substantially reducing its life. Lead acid batteries don’t like going below 50% charge, about 12.2v (approx because affected by other factors). Totally Flattening an old battery can kill it, and can take years off the life of a new battery.

In case it’s of interest, an extract from Some notes I have:

BATTERY FACTS
Charging starts at 13.8v
Charging needs to be >14.2v to recharge in any reasonable time
Gassing starts at 14.4v, becomes damaging at 14.8v, seriously over 15v
Measuring state of charge (SOC) by voltage:
Measure the Open Circuit Voltage of 12V battery after car is off for an hour and a brief discharge. This is not foolproof. It is:
Temperature sensitive - voltage rises with temp
Charging leaves a capacitive charge - brief discharge clears
Chemistry affected by charge, discharge and agitation - ideally the battery should be left open circuit for 24hrs (min 4 hours)!
Calcium added to lead acid batteries to make the maintenance free raises the voltage by 5-8%
Voltage Relative charge
12.6 V 100%
12.4 V 75%
12.2 V 50%
12.1 V 25%
<11.9 V Dead
Full table compensating for temperature here: http://www.meeknet.co.uk/e38/E38_Battery_SOC_Table.jpg

Testing battery and charging system

www.w8ji.com

Charging Information For Lead Acid Batteries – Battery University

Review various Lead Acid charging methods and examine why some systems work better than others. Find also simple guidelines for charging Lead Acid batteries.
batteryuniversity.com
 
BATTERY FACTS
Charging starts at 13.8v
Charging needs to be >14.2v to recharge in any reasonable time
Gassing starts at 14.4v, becomes damaging at 14.8v, seriously over 15v
Measuring state of charge (SOC) by voltage:
Measure the Open Circuit Voltage of 12V battery after car is off for an hour and a brief discharge. This is not foolproof. It is:
Temperature sensitive - voltage rises with temp
Charging leaves a capacitive charge - brief discharge clears
Chemistry affected by charge, discharge and agitation - ideally the battery should be left open circuit for 24hrs (min 4 hours)!
Calcium added to lead acid batteries to make the maintenance free raises the voltage by 5-8%
Voltage Relative charge
12.6 V 100%
12.4 V 75%
12.2 V 50%
12.1 V 25%
<11.9 V Dead
Full table compensating for temperature here: http://www.meeknet.co.uk/e38/E38_Battery_SOC_Table.jpg

Nice table Chris, showing temperature compensation.
 
The engine battery is being used all the time. The ECU is running 24/7 and so is any alarm / tracker thats connected. We had a Swift that had a red button on the ignition lock. Pressing the button and turning the key to the last position cut off all the power from the battery so no central locking or ECU. If you wanted to get in the vehicle you had to use the key and when you switched everything back on you had to reset the clock.
 
Test today seems to confirm it's holding charge. On mains 13.17. Unplugged for 1 hour it read 12.6.Plugged back in it slowly rose back to 13 +. My conclusion is a dodgy connection on the fuse. The act of removal and refitting seems to have made all the difference
 
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