Hi Steve, and welcome to the playground. Not sure if I can answer your questions but your first query is something I've thought about but haven't pursued to date as I've been in a static location in my motorhome for most of the past year permanently connected to the mains, and only used 240v to run the fridge, microwave and laptop while leaving the batteries to power lights, TV, satellite receiver and other sundry things. (I have 3 x 200w panels on the roof feeding 460Ah of batteries via a Redarc 1240 MPPT charger). I have a 40A 240v charger connected to the batteries but have only used it a couple of times at night, and it doesn't appear to have any effect on the Redarc. I'm guessing that if both are supplying a charging current, each will sense when the batteries are full and throttle back the charge as appropriate. I drew up a circuit a while ago which uses a 12v relay to switch the charging source to the mains charger whenever it's powered on, but maybe it's not necessary. I look forward to some answers from the gurus here.

Having a motorhome, I can't help you with the second question except to suggest you provide more information on how your 7-pin plug and Anderson plug are wired. Does a wire from the 7-pin connect to the Anderson plug or do they have separate connections to the battery? Your problem could be due to voltage drop from the tug's battery through the 7-pin plug to the battery, or your tug is fairly modern and has one of those 'energy saving' alternators that reduces output once it senses the vehicle's battery is fully charged. A lot of people seem to use a DC-DC charger located close to the van battery. This is then connected, using appropriately sized cabling, to the tug's battery via an Anderson plug/socket at the rear of the tug. The DC-DC charger should automatically isolate the two batteries when the motor isn't running so that the tug's battery doesn't get drained by the van's battery. I'm sure the more experienced members will help you out (and correct any errors I've made).

Cheers
Joe

Thanks guys.

Peter and Joe, you seem to at least have the same view as I had, which is great.

Joe, part of my reason for asking the question was because I hooked the middle pin of the 7 pin plug up to the same power terminal supplying the Anderson plug. My first trip after buying the van exposed that I didn't have any supply to the middle pin, which meant my Breaksafe wasn't charging and my fridge didn't get the message that it was plugged into 12V. Now, the fridge and Breaksafe seem to work fine. but I don't think my battery is getting charged. I have a feeling that I need to change the wire over to a proper ignition switched power supply.

Thanks again. Any other contributions welcome.

Glad to see you have it all up and running, Steve. FYI I was speaking to a chap at Redarc the other day about an unrelated matter but asked him about connecting another charging source in parallel with the BCDC1240 and he said there'd be no problems.

Cheers
Joe

SteveS wrote:

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Thanks all, I have the panels installed now with a MPPT controller and all seems to be good. It seems the C-Tek will always try and top up the battery off float when switched on, so I can live with that, but they seem to live with each other OK.

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 When you switch on a multi stage charger of any type (mains, DC-DC or solar controller) the charger will go through its cycle. If the battery is charged then the charger will quickly go through the bulk stage to the absorption stage and when the charging current reduces sufficiently it will switch to float charge.

Back to your original question - you should only connect multiple chargers to a system they should all be multi stage chargers. That way they will all go through the same cycle. They will all have slightly different set points for their absorption charging. When you commence charging a discharged battery they will all contribute to the charge current of the battery. As the battery charge level rises and consequently the battery voltage rises the charge current will reduce. When the terminal voltage rises toward the absorption voltage set point the charger with the lowest set point will reduce its current first and switch to float voltage. This will happen to the other chargers until there is only one of them contributing absorption charging current. That charger will continue until the last charger completes the charging and it in turn will switch to float charging.

That is the technical explanation of how multiple chargers can line together.