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 Topic: Using fridge whilst towing
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25/3/2025 at 12:53pm
Location: East Herts
Outfit: 1992 Elddis Wisp 450CT + X Trail
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As far as I know it does get charged as long as you have the socket on the car fully wired up. I understand that some installers don't wire them fully. I have the old system so I don't know for certain, but I'm sure you shouldn't get less than the old system provided.
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Best Regards,
Colin
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25/3/2025 at 3:45pm
Location: London
Outfit: Lunar Cosmos 524
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Well, in principle at least the 13 pin plug/socket MOST CERTAINLY do have the capability of both charging the on board leisure battery AND running the fridge IF the car mounted socket is fully wired (but only when the engine is running above tickover speed), but they are NOT always fully wired, not too uncommon to find sockets only have basic, legal requirement lights connected, so no fridge or battery charger! It's a budget installation!
Then of course there is the declaration from the dealer/seller, which may indicate that there is a unfixed fault with the caravan, causing it not to charge when towing - THE USER MANUAL CATOGORICALLY STATES that the battery WILL charge when connected to the car (subject to tow bar electrics being compatible!). The caravan system should automatically sense when the car is supplying the necessary voltage and switch over to appropriate mode.
See user manual, section 6-1: https://manualsnet.com/compass/casita-touring-2019
There is a bit of a grey area with more modern cars (post circa 2016, Euro 6 rated, part of the emissions/economy standards) where what are known as 'Smart Alternators' only charge the car battery (and raise the 12v system voltage sufficiently) under certain conditions, like on overrun, or when car battery voltage drops sufficiently to require a boost charge, which can impact on whether caravan chargers and fridges work when being towed! BOTH require the supply from the car to be higher than the nominal 12v of the system, and with a running engine it would normally be 14.5v or so from a normal alternator, or when a Smart Alternator has 'kicked in'. There doesn't seem to be consistency across makes/models on this point! My 2017 Euro 6 rated car most certainly both operates the fridge and charges the caravan battery during towing, and consistently, now I've never been able to find out if that is due to the completely enabled towbar wiring that is fully integrated into the car computerised system, or just a fluke!
My gut feeling is torn between the dealer not knowing what he's talking about, or he's fudging on an electrical fault on the caravan! Did he do a socket test on your car to determine if fully or only partially wired? - if he did, he may be commenting of the capabilities of your car towbar electrics, rather than the actual caravan!
It's not too difficult to check for yourself, if you are charging the leisure battery when hitched to the car (with engine running at about 2000rpm). Good chance the control panel will show the leisure battery voltage. If around 13.5-14.5v, it's being charged, panel may even indicate 'charging'! Failing the panel being any use, a voltmeter across the battery terminals will give similar indication. Below 13v - NOT charging, 13.5-14.5v - charging.
Good luck.
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25/3/2025 at 5:39pm
Location: London
Outfit: Lunar Cosmos 524
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80A/115A is around 70% SOH (state of health) reading for the battery, which without the SOC (state of charge) reading can be slightly misleading, it may be influenced by discharge level and be slightly better if fully charged. It does suggest the battery may be past it's best though, and maybe you shouldn't expect too much more life from it. My test meter will declare 'Replace battery' if SOH drops to 60%. The decline in health tends to be a slippery slope, once it starts getting significant, the end is nigh!
It may have a date of manufacture or installation label on it, anything more than 4 years life on a well cared for battery is a bonus, but not unknown for a few to soldier on to 8-10 years. Mine is 8 years old and only this winter has dropped to 75% SOH, so thinking time to replace before it dies completely at an inconvenient time - at 8 years old it doesn't owe me anything!
Motor Movers are a pretty heavy load, generally (inverters aside) the hardest load a caravan battery deals with, BUT generally only used for a few minutes at most at any given time. They will separate the men from the boys! - if a battery is on it's last, the heavy load will drop the voltage sufficiently whereby the MM low voltage protection may kick in and it will not work, or will start and stop soon after in a jerky manner, making it's use difficult and unreliable.
Lead Acid batteries have a natural and unavoidable self discharge characteristic, but a lot of variables come into play to determine how good or bad that is! Firstly the 'quality' of the battery plays a part, some have chemistry that gives better characteristics than others. Temperature can effect it as well, below freezing and above 27C worsen the effect. Some say expect charge to drop up to 10%/month from self discharge. If you have an alarm or tracker etc. on the caravan, it WILL (unless entirely self powered) drain the battery over time. It's wise to check the state of charge of the battery every 30-60 days max if in isolated storage, and top up the charge. Better is to keep it on a maintenance trickle charge throughout storage. If the charge level drops below about 55% and is left like that for more than a day or so, it will irreparably damage the battery, and reduce it's effective capacity. You can kill a brand new battery stone dead inside a year with neglect! - and most warranties will not cover that!
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26/3/2025 at 7:36pm
Location: West country
Outfit: Mondeo
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In truth the caravan battery will get very little charge from the car when towing. The alternator voltage is controlled to charge the car battery which is right next to the alternator under the bonnet.
The leisure battery is in the caravan which could be 20 feet or more away. There will be voltage drop in that length of cable meaning the vast majority of charge will take the easy route into the car battery.
When the car battery is charged the alternator output will be reduced considerably as the car battery doesn't need it.
Maybe nowadays they have realised this and just given up on the option.
The fridge operation is a simple heating element which can operate on reduced voltage although it is always highly recommended to cool the fridge on mains at home before traveling as cooling while driving is very much reduced compared to mains operation.
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26/3/2025 at 8:53pm
Location: East Herts
Outfit: 1992 Elddis Wisp 450CT + X Trail
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Strangely enough, with our first two caravans back in the late 1970s, I fitted a leisure battery in the caravans and a split charge system in the car, and despite the car only having a dynamo at first, it charged just fine. I did use some quite hefty cable though. I used to tour more back then, and travelling between sites put enough charge into the battery for a few days use. It was the only way I had to charge the battery as no sites that we used had EHU back then. Neither caravan had mains electricity anyway.
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Best Regards,
Colin
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27/3/2025 at 9:52am
Location: Yorkshire
Outfit: Car & Caravan
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A lot of towbar fitters only wired the towbar for towing a trailer, the better ones asked if it was for a caravan and wired them up to charge the caravan battery and work the fridge.
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30/3/2025 at 3:07pm
Location: Llanidloes Powys
Outfit: Skoda Yeti SEL4x4 +Bailey Ranger 460-4
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OP doesn't state what car they have, so an accurate answer really can't be given.
For example, I tow with a Kia Niro hybrid and that cannot have fridge or battery connections, due to the hybrid system.
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31/3/2025 at 7:12am
Location: Essex
Outfit: Lunar Delta TS 2017
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Just a thought, you are turning the fridge over to battery on the fridge panel?
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Claire and Colin
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31/3/2025 at 6:30pm
Location: London
Outfit: Lunar Cosmos 524
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Quote: Originally posted by LlaniDavis on 30/3/2025
OP doesn't state what car they have, so an accurate answer really can't be given.
For example, I tow with a Kia Niro hybrid and that cannot have fridge or battery connections, due to the hybrid system.
I was aware of no auxiliary power with full EVs, but first time I've heard of it on a Hybrid! That's not good news, as apart from fridge and leisure battery charger not working, which is an inconvenience, it also means ATC won't work, which is a compromise on safety! The loss of those three, which I do put to good use (well ATC only as a last resort and in theory so far!) would definitely put put me off that as a tow car!
Your point of not knowing the OPs vehicle is a good one which none of us has questioned so far, just made assumptions about why no battery charging, it really may not be an option at all!
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via mobile 25/3/2025 at 12:40pm
