Thoughts on charging caravan battery from car!

[Keithmac]

Out Trailer Module is Canbus connection to car, monitors all trailer/ caravan lighting etc.

It also put the car into "Trailer Stability Mode" to assist with any snaking that may occur. Our 'van doesn't have ATC but the 13 pin was checked for compliance when fitted.

Iirc the 7 pin systems are NOT and MOT check but the 13 pin systems are.

All my wiring was done in the boot, no wires cut or "piggy backed", it was a Dedicated Trailer Module specific for our car that was fitted.

On a long run the battery is fully charged and the fridge remains cold, if you turn engine off at services you have to turn the control pannel back on in the caravan before setting but that's the only "quirk".

 

[ericmark]

In the old days I could stick a hydrometer into the battery and measure state of charge, caravan was often taken to Mid Wales about 1.5 hours from home in North Wales, the old Lucas blocking diode never worked, but the relay did to some extent, using 65/0.014 cable both to caravan and to box in boot of car, a 60 Ah battery after starting the car would show a good 10 to 15 amp charge, and depending on car battery some times up to 20 amp.

So with a battery where fully charged was 1.260 starting at 1.200 it would reach 1.210 in caravan and 1.220 in the car, in dad's car boot over 6 days it would go from 1.200 to 1.245 that's 2 x 1.5 hours plus daily run to work, but only way to get it right up to 1.260 s.g. was to swap prime mover and slave battery over. However it was enough to allow us to watch TV for one hour a night. And easy enough to measure how much power in the battery.

However today we can only measure volts, at 12.8 volts the battery with no load or charging for an hour should be fully charged, however experiments have shown how a sulphated battery can take weeks to recover, seems odd but that recovery once it starts is quite fast, but we can't really measure how much energy has actually gone into the battery, and even with the narrow boat with 6 hours a day with engine running the batteries never fully recharged unless one could get a shore supply for a day or two. So if you wanted batteries to last, once a month you needed a shore supply.

So on leaving home caravan battery 95 Ah fully charged so trip to camp site does not really matter if it charges or not. All the 13 pin socket does is work fridge, and if switched on before leaving home full of food, even that does not really matter unless travelling for over 5 hours.

Even with a DC to DC inverter say 20 amp stage charging charging will only go to 80% as at that point charge current drops, and we simply do not tow for long enough to fully recharge battery, so best case for 5 hour drive around 65 Ah into a 95 Ah battery, but a 10 amp charger would still put in 50 Ah and less likely to cut out on under voltage. As to simple relay likely only 20 Ah however that is better than nothing, and enough to allow a few nights off line as long as once a week you find a site with hook up.

However a inverter generator say 2 kW will allow one to cook using microwave and induction hob, and vacuum the floor, and running for just 1 hour a day will likely replenish the battery just as much as a 5 hour move site to site using a voltage dependent relay. Add a small solar panel and you have as much as one could possibly hope to get with a DC to DC inverter.

Or so it seems?

And this is the problem, people are unwilling to say, I made a mistake, I bought a generator, solar panel, fitted a voltage dependent relay, a DC to DC inverter or any other device and it would not fully recharge my battery so on arriving home had to recharge battery from mains before I could take caravan around back of house with motor mover.

So nitty gritty what I want is if the last site is without hook up, and 3 hours from home, and I get battery down to 5% charge before leaving, for enough power to go into battery to run motor mover to get caravan around back of house, from charging times using fully charged battery and recharging after I need around 20 Ah of power. If I can't get that much, then alternative method is a charged battery at home. Or a caravan small enough that I can tow it to behind the house and not use motor mover.

What I don't want to do, is spend a few hundred pounds on a DC to DC inverter, then still have to swap batteries when I get home.

So a report that says went to Scotland, the battery would no longer work TV, travelled home for 3 hours (miles don't matter it's time that matters) and the motor mover got caravan up the curb and failed, or got caravan around back of house 40 yards and failed, or got caravan to back of house and in storage position around 50 yards. And I have a car with/without power saving charging, and am using a voltage dependent relay/10 amp DC to DC/30 amp DC to DC and caravan is 950 kg/1250 kg/1500 kg etc.

Living in Scotland and taking caravan to France sleeping on ferry so 4 hours to ferry and 8 hours once off ferry and one would hope any car charging system would put enough into battery to work motor mover when they get home. I however living in Mid Wales and now no passport am unlikely to tow for over 3 hours. Even before the car which switched off charging, I know with a voltage dependent relay 65/0.014 cable moving every other day, I was limited to around 1 hour a night TV, at that time no motor mover, at end of three weeks holiday battery was about flat. Without the charging from car would have only lasted a week. So when people claim their voltage dependent relay keeps the battery topped up, I wonder if we are living in same country?

 

[Harry Bloomfield]

It takes a very long time to recharge a lead acid battery, usually around 24 hours on charge to get it back to full capacity. That whether it is in a car being driven, or on a separate mains charger. The reason is that both car and chargers are limited by output voltage of around 14.2 to 14.5v and the charging current is limited by the battery itself to around 3 to 5amps.

On site I use mains hook-up, but a mover to get the caravan out from the back of my long drive and to set up on site. My battery is really on used for the mover, or when I stop somewhere on route to a site, or when the site mains is interrupted. All of my lighting I have converted to LED, to save power and avoid unwanted heat - it has 17 lights in it

At home I use a regime of having the caravan hooked up, but the battery disconnected. I reconnect the battery once every month or two, for 48 hours, to bring the battery back to a near full charge. The present battery is good and has been in use for over five years. I used to leave the batteries powered, to keep them charged, assuming 13.8v would not harm them, but it cost me two batteries, hence my revised regime.

 

[Keithmac]

For me I would have a spare battery ready go at home so you can use the mover to get the caravan on the drive asap. Optimate or CTEK will sevice charge and maintain a spare.

Alternate two batteries so they get even use?.

We always go for EHU on sites so the caravan battery is always charging, even after a 7 hour tow from Cornwall our Powrtouch mover worked a treat putting it back in storage.

 

[ericmark]

Thank you both, I have also wondered about leaving on charge or not. I have a Lidi charger similar to Ctek and with a A1 battery at 14.4 volts it switches off, and at 12.8 switches on again. So most of the time sitting at 12.9 volts, that's OK, but if the battery is not A1 then does not hit 14.4 volts so continues to charge, may be only 0.1 amp, but still my reduce battery life further.

At moment no option can't reach battery isolator so there is a drain on battery, so left on charge 24/7 caravan 1 foot to long to go in A frame last, can't open garage door, and A frame first means doors against hedge.

But moving in next few weeks so looking for storage. So looking at new methods to look after caravan and batteries.

 

[Harry Bloomfield]

Just switch it on and off at the mains socket.

 

[Keithmac]

Thank you both, I have also wondered about leaving on charge or not. I have a Lidi charger similar to Ctek and with a A1 battery at 14.4 volts it switches off, and at 12.8 switches on again. So most of the time sitting at 12.9 volts, that's OK, but if the battery is not A1 then does not hit 14.4 volts so continues to charge, may be only 0.1 amp, but still my reduce battery life further.

At moment no option can't reach battery isolator so there is a drain on battery, so left on charge 24/7 caravan 1 foot to long to go in A frame last, can't open garage door, and A frame first means doors against hedge.

But moving in next few weeks so looking for storage. So looking at new methods to look after caravan and batteries.

My weekend car got very little use and was constantly on the Optimate, it always started and the battery was at least 8 years old when I replaced it.

If you turn it charger off it won't drain the battery just being connected.

We bring our battery home after a trip and pop it on the Optimate for a day, then a day before we go away again.

Our drive is about 2 foot too short to fit the caravan on, but to be fair it's better off in storage, some days we struggle to get the car out due to bad parking/ inconsiderate parking so no chance getting the 'van out!.

 

[Harry Bloomfield]

My weekend car got very little use and was constantly on the Optimate, it always started and the battery was at least 8 years old when I replaced it.

If you turn it charger off it won't drain the battery just being connected.

We bring our battery home after a trip and pop it on the Optimate for a day, then a day before we go away again.

That depends upon the Optimate, the early Optimates would discharge a battery if left connected to the battery with no mains power.The charge state LED's would continue to operate when mains was absent and discharge any battery it was connected to. Terrible design idea, who ever thought that up should have been shot. It is not unknown for power to be lost in a garage or a shed where a battery might be on charge and not to be noticed for hours/days/weeks..

As said I have wrecked batteries in the past by leaving them on a controlled charger before. Warmth from the small continual charge causes them to evaporate the electrolyte. The best way is the battery completely disconnected from all loads, then brought up to a full charge occasionaly.

 

[ericmark]

As said I have wrecked batteries in the past by leaving them on a controlled charger before. Warmth from the small continual charge causes them to evaporate the electrolyte. The best way is the battery completely disconnected from all loads, then brought up to a full charge occasionaly.

I have also wrecked batteries leaving them discharged, the Lidi battery charger needs one to press a button to start it charging, it selects between small and large and also frost charging rates, so switching it off then needs some one to manually turn it back on again. The caravan main charger is set on for one hour a week normally, and the power in is recorded so if the hour charge rate is higher or lower than normal I will check, but at moment all my Engenie stuff is packed away ready for move, so no monitoring.

As to if more batteries died due to other charging than under charging hard to say, stair lift batteries when used would last 4 years, not used 2 years as it relied on the battery being discharged at least once a day to keep voltage down.

But what I was considering is if charging from car is worth while? But caravan forum people claim battery fully charged while towing, and I know with a narrow boat with engine running for 8 hours it was not long enough to recharge batteries, so it seems unlikely anyone would tow a caravan for 10 hours or more, so I have to conclude they are mistaken and the battery has gained some energy, but not fully charged.

So four methods to charge battery.
1) Use a site with electric hook up.
2) Charge from car.
3) Solar or wind charger.
4) Small generator.

I am leaning towards small generator, as while running can use induction hob and microwave, so it would be start up to do cooking then turn off again unless battery that discharged that we have no lights, and try to use in the main sites with electric hook up. There is the anti-social noise issue, but 1/2 hour for cooking and an inverter generator should not really be a problem.