Using camper battery bank/solar to recharge other battery banks (such as boat batteries).

[Chadx]

Thought I'd start a thread about using your camper battery bank/solar to recharge batteries on another battery bank. This came up on a recent thread so thought I'd start a new one to discuss. Though in my application, I'd be charging batteries in a fishing boat, this thread isn't isolated to just boat batteries as it applies to charging any batteries that are not part of the camper battery bank.

On my FWC with 180 watt solar panel, I have a lot of excess solar capacity going unused each day. I've been considering options to harness some potential current being as 50% of our trips include pulling the fishing boat which is rigged with 4 batteries (one main starter battery, two deep cycle electric trolling motor batteries, and one deep cycle for kicker motor, live well, sonar, downriggers, etc.) The starter battery and kicker battery are fine as they recharge off of the alternator of each of those two gas motors, so I'm looking at pushing the current into the two electric trolling motor batteries.

The simplest scenario would be to fashion cables to go from my camper battery bank to the boat batteries. I have a good handle on which boat batteries I'd charge and how, so won't dive into the specifics of that layout, but I want to at least note that those with trolling motor batteries hooked up in series (for 24v and 36v trolling motors) should take care in how you plan to charge since you'll be charging with 12v source. It is fine as long as you hook the 12v source up to ONLY the terminals on one of the batteries at a time (12v to 12v). Don't connect a 12v source to a 24v or 36v battery bank by spanning all the batteries in series or you'll be mismatched voltage wise. It's important to understand how the wiring must be attached).

For me, it is probably not worth the extra expense of purchasing a portable solar panel and controller specifically for this purpose, but for some, that might be the best way to do it. But with my current setup, I'm at 100% charge by noon so have extra potential going unused so thinking I might as well consider options. Note, since installing the solar, I have disconnected the camper batteries from the truck battery since the solar has performed so well. I still have the wiring in place in case I ever need it.

Length of cable runs and associated compromise between cable length, voltage drop, and cable size will need to be a consideration. We typically unhook the boat/trailer and pull the camper next to the boat, which would shorten those lengths compared to stringing wire to a trailer in the tow position, however it would limit charging to being parked and unhooked. I can see there being times where it would be convenient to charge the boat batteries while towing, such as driving from one location to the next.

I'd probably attach a pigtail to the camper battery bank and run that through the shunt so my trimetric knows what current is going where (which it wouldn't know about if I tied directly to the battery bank). Other than that, should be pretty straight forward.

I may not even end up doing it, but fun to go through the mental exercise and I'm curious if others are charging external battery banks.

 

[rando]

There was another thread about this recently:
http://www.wanderthewest.com/forum/topic/14909-fwc-factory-twin-battery-parallel-hookup-question/page-2?hl=trolling#entry177389

I think your best bet (which Wandering Sagebrush proposed) would be to wait until your camper battery is fully charged, then unhook your solar from your camper battery and hook it up to each of your trolling motor batteries. You want to avoid your trolling motor batteries pulling your camper batteries down. You also don't want to do this with your battery monitor in the circuit as it will screw up the charge accounting and you will have lost track of the state of charge of the camper battery.

 

[craig333]

I was about to say go for it but I never considered the charge accounting. You could run the panels into a separate controller just for charging the other batteries.

 

[Vic Harder]

I was about to say go for it but I never considered the charge accounting. You could run the panels into a separate controller just for charging the other batteries.

This isn't necessary. I think rando's comment was a warning, not a "don't do this".

Think of this as the same as how the truck and camper are connected through an isolator from the factory. In ideal situations, the alternator charges both battery banks, and in the sunshine, the PV panel does the same. The shunt that measures the camper battery status is in the ground leg of the camper battery circuit, and doesn't measure what happens to the truck batteries.

To meet Chadx's needs, I think a switch to uncouple the output of the charge controller from the camper batteries, plus a set of 4g wires from the solar controller output to the outside of the camper (go through the floor pack) to a set of anderson power poles accessible from the outside, voila.

I'd rewire the trolling motor batteries in parallel for charging purposes. Charge them all at once. Ideally you would reprogram the controller to meet the specs of these batteries, assuming they are different than the ones in the camper.

 

[rando]

I think the issue is that the Bogart charge controller won't work without the battery monitor. The easiest solution may be to buy a separate charge controller for the boat batteries.

 

[Chadx]

There was another thread about this recently:
http://www.wanderthewest.com/forum/topic/14909-fwc-factory-twin-battery-parallel-hookup-question/page-2?hl=trolling#entry177389

I think your best bet (which Wandering Sagebrush proposed) would be to wait until your camper battery is fully charged, then unhook your solar from your camper battery and hook it up to each of your trolling motor batteries. You want to avoid your trolling motor batteries pulling your camper batteries down. You also don't want to do this with your battery monitor in the circuit as it will screw up the charge accounting and you will have lost track of the state of charge of the camper battery.

Thanks Rando, I remember looking at that thread before it changed topics onto charging a boat battery. Good info. If I hook this up, I believe I would want to hook my negative to the shunt so the shunt and trimetric are in the circuit because I'd want the trimetric to keep track of juice flowing into, or out of, the camper battery bank. If it went around that by connecting directly to the battery bank, then the trimetric woudn't know about it. I want this to be a trackable draw just like any other circuit (fan, furnace, fridge, etc.). Hooked up like that, I wouldn't need to unhook anything, unless, like I'll mention later, I unhook the panel from the controller and use a second controller near the boat batteries.

...
To meet Chadx's needs, I think a switch to uncouple the output of the charge controller from the camper batteries, plus a set of 4g wires from the solar controller output to the outside of the camper (go through the floor pack) to a set of anderson power poles accessible from the outside, voila.

I'd rewire the trolling motor batteries in parallel for charging purposes. Charge them all at once. Ideally you would reprogram the controller to meet the specs of these batteries, assuming they are different than the ones in the camper.

Anderson plugs is what I was thinking. As noted above, negative cable to the shunt and positive to the battery positive post, just like any other circuit, so the trimetric is aware of what flows in and out of the battery bank. Much like any other circuit (fridge for example) if the solar current is flowing to that curcuit and not making it to the camper battery bank, the trimetric does not and should not record it. When I have the solar producing 7 amps and the fridge kicks on and pulls three amps, the trimetric shows a positive of 4 amps because that is what is going into the camper battery bank. In the boat battery scenario, the juice flowing to the boat batteries from the solar controller would not be logged if it all goes to a lower amp boat battery rather than the camper battery bank. And if the camper battery bank has juice flowing outward, it would show a negative on the trimetric. Exactly what I'm after.

This would allow me to know if the boat batteries are drawing only from solar or also from the camper battery bank and if so, how much, and I could monitor the percent full of the camper battery and decide at what point to unhook the boat batteries. For example, if I use a large enough gauge that the entire output of the solar panel plus 3 amp/hours of camper battery current flows into the boat batteries, I could charge until the camper bank was down to whatever I was comfortable to start the night with. Say 90 percent since I know I typically use less than 10% charge overnight before the solar starts recharging. So I know I'd still be at about 80 percent charge if I start the night at 90 percent.

Regarding the cable gauge, that would be about the only thing limiting the current flow. So I'd have to decide between extra large to charge them faster or medium to allow for some voltage drop to slow the charge so perhaps the solar panel produced current is flowing to them but no draw off the battery.

Or scrap that entire idea and put a switch on the solar panel wiring and a cheapo controller in the boat so the 18v - 19v from my solar panel can travel across a smaller gauge wire, like 10 or 8, get chopped at the controller to 14+ and charge the batteries that way. Would have the extra expense of the second controller, but cheaper, lighter cable because the voltage would be pre-controller rather than post.

To elaborate on my previous warning about 12v, 24v, etc. that was intended for those not familiar with batteries in series and who might accidentally hook a 12v source to a 24v. Two 12v batteries wired in series can easily be charged with 12v sources. The 12v sources simply needs to go to each battery individually. Boat batteries are typically charged with a 12v charger with the same number of banks as you have batteries. So a 24v system has two batteries and a boat charger has two 12v charging bank with each bank wired to each 12v battery directly. 36v has three batteries wired in series but the chargers are typically three 12v charging circuits; each wired to one of the three batteries. I charge my current two trolling batteries with two 12v battery tenders, each tied to one of the two batteries. There may be some issues with connecting one source to two batteries that are also wired in series though. But with separate charge sources, no issues.

I think the issue is that the Bogart charge controller won't work without the battery monitor. The easiest solution may be to buy a separate charge controller for the boat batteries.

The Bogart 2030 controller can be used in stand alone mode without the trimetric 2030 monitor. There are two switches on the controller itself. One to set for 12v or 24v panel and one to set for AGM or regular flooded. The controller not as smart as if programmed with a trimetric parameters, but it can be used stand alone.

Point on the second controller taken. Not really any easier, just wired different. Pros and cons to both (some I mention above). But I agree, a second controller is just as good of an option and wiring through my main controller. Just decide where I want the expense tt be. Second controller and smaller wiring straight from the panel, or through my current controller where I save the expense of a second controller but have to use a heavier gauge wire to account for voltage drop. And since I'd mainly be concerned with bulk charging for limited periods of time, plus the available amps would be small, the second controller could be a rather economical unit. So that is one more pro for that route.

 

[rando]

Thanks for the detailed explanation. If you do end up going with a second controller for customized parameters and smaller cable - theses are (relatively) cheap and good: http://shop.pkys.com/Victron-Energy-MPPT-7515-Solar-Charge-Controller_p_2779.html

 

[ntsqd]

The Morningstar Sunsaver Duo has two outputs. Can set it to split the charge between banks at 50/50 or 90/10

 

[Squatch]

I think the issue is that the Bogart charge controller won't work without the battery monitor. The easiest solution may be to buy a separate charge controller for the boat batteries.

Sure it will. The SC2030 will work as a stand alone. Just not as precise. In this mode it uses generic profiles. I'm thinking of just picking up a sc2030 and using that to charge the AGM's in my boat with my portable panels. To me that's simpler than jumping through hoops to use the camper charging system.

When I installed my solar stuff. I ran a set of 8 gauge cables from the common positive and negative lugs I installed (Think the points where the truck battery meets the switch) to the outside of the camper. I have an Anderson connector on this. The original idea was to extend cables to the truck cab to run the fridge in the truck off the camper battery. I never did that So I just use this as a High amp aux hookup for things like my air compressor. This is all downstream of the shunt. So if I hooked this up to an external battery to charge it. The Trimetric would just see the aux battery as a high amp load and would compensate for it. But the warning is that If said aux battery was low and it was cloudy then yes you could draw down the camper battery.

The one that has me stumped is High voltage battery charging. I'm going to convert one of my bicycles to an E bike with an electric assist motor. The batteries are 52volt Lithium Ion. The only safe way I can figure to charge these off the solar is to use an inverter and the regular 110AC charger. Just doesn't seem very efficient.

Safety note. I have 3 external Anderson power poles connectors on my camper. They are color coded. Different colors will not mate.
I use Red for truck battery to camper connection. I consider it an Input.

Orange for aux solar panel in. This is wired to and in parallel with the roof top solar pre-solar controller. Also
considered a specific input. All my solar cables and portable panel have orange connectors.

Blue for the above mentioned external Output for loads such as fridge or air compressor. I consider this an output even though is is wired to the same common posts as the Red connector from the truck.