using the tow vehicle alternator for charging

G'day Jay, Voltage drop over the length of the cables can be an issue and high current draw if you have a situation where the batteries are flat and you start engine. Most of us have the provision using Andersen plugs at the towbar. Cable of 35 sq mm would be nice but is big in diameter. As a compromise use as large as practical in cross section. This is my opinion only ..... I have a current limiting device (circuit breaker) in the circuit from the alternator to the van batteries to stop high amp draws if the batteries are flat as a precaution. As you said .... and I agree ...if using the vehicle as a prime source of charging I'd be fitting a high end three stage alternator charge regulator and mount it away from engine bay heat. As you probably know an alternator is not the ideal charger for deep cycle batteries without a good regulator and I would use the car alternator as an emergency charge means only. I have 4x 120w solar panels capable of 30 amp in prime sun ..... then a Honda 2.0 genny with a Victron 30 amp three stage charger .... if both these are not able to be used I'd hook up the Andersen then ...... The Honda/ Victron combination also allows me to charge the vehicle start batteries if the need arises (2x start batteries and 2 x Sonnenschein Solar Blocks in F250) Others that are on the road for longer trips than myself might like to comment about if it is really necessary to use the car charge anyway ??? Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker

Anthony On the boat the cables from the alternator to the batteries were true 00 battery cables - big as you thumb !! Are the Anderson plugs carry the juice from the alternator to the ban batteries? With regard to an alternator regulator it was a rather simple device that was hooked to my monitoring systems. When we were running the engine during a passage I simply watched the output of the alternator and the voltage of the batteries and adjusted the regulator so that the voltage never went over 13.8. Once set it was rarely necessary to change the setting. A three stage charger worked off of the generator or shore power. I did not have solar on the boat so that will be new to me. We will have the newer 125w solar panels x 4 and that may well be sufficient. Simply like to have lots of redundancy. What batteries and how many do you have in the BT? Primarily, if I understand correctly, charged by your solar panels. What is a Sonnenschein Solar Block in F250? Look forward to other comments on this issue. Cheers, Jay

Re charging from car alternator. As Anthony says, a standard car alternator/regulator will not charge conventional lead acid batteries beyond 70%. In practice 65% is more common. A smart regulator is one solution but they are not compatible with the ubiquitous computer engine management systems. Sterling (UK) company has a new system that supplies the vehicle's needs directly from the alt/reg - but uses a dc-dc converter plus three step regulator to provide the house batteries with whatever they need. As the alt/reg remains standard this can be used with any system. However. Do you need to charge the house batteries from the car alternator at all? Depends. If you drive a fair way every day it makes sense to do so. It you spend a week or more on site away from mains power - it doesn't If you'll forgive the mention - my two new books 'Solar That Really Works' (I producede both caravan and motorhome editions) make out a strong argument for going electrically self-sufficient via solar and not bothering with alternator charging at all. I changed the OKA over to this some years back and never regretted it. A useful benefit is that the regulator can be set up to provide an optimum charging regime for the battery type used. You can use a conventional starter battery, and (say) gel cell batteries for 'house' use. ('Caravan and Motorhome' magazine is running a two-part piece of mine re just this early next year.) Without alternator charging it's best to use a really good three-way Climate Class T fridge - and either leave the microwave at home - or use it only where there's mains power. Though if you've read the latest research in New Scientist re what microwaves ovens do to food you'd not use one anyway!. If you do want to stay with an all-electric fridge, you really do need generator back-up.. But if you go that way you are spending some $5000 to run a $2000 fridge. If you elect for a microwave you are spending $2000 to run a $275 oven! What c ould have been a $3000 system could cost $10,000. But it's a personal choice and I do accept and state that the all-electric approach is marginally more convenient. Trust this helps Collyn Rivers

Have installed a dedicated alternator and volt meter (which gets me into compliance with NSW regs re driver's position monitoring of break-away battery condition). The alternator runs through 2BN battery wires to a 175A Anderson plug, then a circuit breaker (which allows me to isolate the van batteries from the Anderson plug when van is off tow - so no smarty can short it out). Seems to work OK so far, though I am now having the regulator fine-tuned to give optimal charge profile. Griff