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Old 08-27-2012, 09:03 PM   #1
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Solar regulator and alternator sharing ground.

Hello! I was wondering if anybody might be able to help me with some information. I'm midway through putting together my camper van and had a question about grounding the solar regulator and alternator.

What I would like is for the alternator to be charging my house battery while I am driving, then while parked I will use the solar panels to top them off. I currently have just the solar panel hooked up to the house battery and it is working fine. I want to hook up the alternator to the input of the solar regulator. Can I just bring in a positive wire from the alternator itself and ground the negative of the solar regulator to the chassis? Is it alright for the two systems to be sharing a (chassis) ground?

I'm thinking that the positive wire from the alternator will just have a simple switch (or maybe relay, if I can find a cheap locking magnetic one). I will just manually shut the switch off when I am not driving. I would use a diode/isolator but I'm a little worried about the voltage drop.

So to sum up, can I connect the negative side of the solar reg. input to the chassis ground?

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Old 08-28-2012, 09:24 AM   #2
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Re: Solar regulator and alternator sharing ground.

Your van should only have one ground for the 12V systems, and it is shared.

When you mention connecting the alternator output to the solar regulator input, do you mean to the solar regulator output? Why would you want alternator power going through the solar controller? There is enough power there to destroy the solar controller.

The alternator output is regulated and doesn't need a 2nd controller.

I don't know what your van is, SMB, homebrew, stock, or other, but if it is an SMB, it should have a battery separator or isolator to charge the house batteries from the alternator and the starting batteries from the solar system. So the connections may already be in place.


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Old 08-28-2012, 10:18 AM   #3
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Re: Solar regulator and alternator sharing ground.

Just connect the house battery + to the starter battery + through some from of isolator, and connect the house battery ground to the chassis (if it's not already done). That will do exactly what you want.
The idea of the isolator is to separate the house and starter batteries when the alternator is not charging, so your house "appliances" only drain the house battery and you can always start the vehicle.

Isolator can be a simple relay that you switch on while driving, RV style isolator that's uses diodes (not my personal recommendation), or a intelligent relay like the BlueSea ML-Series

Don't connect the alternator to the charge controller input, you'll kill the charge controller.
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Old 08-28-2012, 01:15 PM   #4
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Re: Solar regulator and alternator sharing ground.

Something to keep in mind, some solar charge controllers are fussy with how they are wired so check the manufacturers documentation to be sure. Some of them have to be connected directly to the battery positive and negative terminals to work (sense) correctly and some have restrictions on wire length and size from the controller to the battery. No matter who makes them they are designed for solar type voltage (a wide voltage range with very low amps) input, not an alternator power output (minimum voltage range and very high amps) so do not hook your alternator to the solar controller.

There are many excellent threads here on the forum about charging systems and batteries you might want to brush up on them before you do any work or buy any parts. You cannot just hook your alternator to your solar charge controller as SheepShagger stated. Even is you use a manual switch (not recommended by the way) it has to be able to handle a lot of amps when the battery is low and the alternator is trying to charge it fast. I would pick a relay (my personal choice) designed for dual battery charging (meant to be constant on not momentary like a starter relay) or isolator kit and read about the recommended wire size for the distance needed as recommended by the manufacturer and use that as a guide line for your installation. Since you are using solar you don't really need a latching relay if you are thinking of saving a little bit of power. I have been using a factory Ford dual battery relay (F8UB-14088-AA) for all most two years with no problems at all.

Always be sure to use the recommended wire size and fuses for any electrical systems you do to your van.

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Old 08-29-2012, 03:16 PM   #5
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Re: Solar regulator and alternator sharing ground.

Hey thanks for the responses. Yes it is a homebrew van I'm putting together, most the cabinets and everything are built, just working on the electrical now. I've got 160w of panels installed with a 200aH battery bank and a Morningstar 10A solar controller.

Yes I did mean the output of the solar regulator, I don't know why I wrote down input. What I ended up doing was grounding the negative terminal of the battery to the chassis with some #2 wire, then splicing in a #6 wire that goes to the negative of output of the controller. I'm assuming that while the alternator is charging the battery, the solar controller will sense that and just go into float mode?

So what I planned on doing then is simply wiring from the positive terminal of the starter battery to the house battery bank. My alternator is rated at 105amps, so I'll get an appropriately sized relay to be hooked up to the ignition "ON". ( They have some pretty cheap 200A ones on Amazon for this purpose.) I wanted to stay away from diodes and isolation because of the voltage drop, and the more advanced separators (like the blue sea one) are out of my budget for now.

Maybe its better if I just get a cheap isolator and use that for "bulk" charging the batteries from the alternator while driving, then rely on the solar to top them off with the proper voltage? Would the diode voltage drop really matter then if I have the solar? I have a limited budget for this project right now.
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Old 08-29-2012, 03:47 PM   #6
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Re: Solar regulator and alternator sharing ground.

Originally Posted by diegotheslinger
I'm a little worried about the voltage drop.
I'm unclear why this is an issue. The wheels don't fall off and the van doesn't catch fire because of a voltage drop- True I wouldn't buy the dead cheapest Isolator, but I wouldn't spend time building around voltage drop either.

I would got separator over isolator too, in fact I'd get a separator before solar or something else that's easier to add later (not part of the core power system). Still until 2003 most all Sportsmobiles were built with an Isolator so you don't absolutely need a separator and I think you'll be fine with a decent isolator.
and then
everything changed
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Old 08-29-2012, 09:15 PM   #7
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Re: Solar regulator and alternator sharing ground.

So it sounds like you are going in the correct direction, though you're first explanation got me off track. For your house battery just try to tie most of the grounds to the frame in the same location. So yes .you can use an appropriate sized relay and join the the positive side of the two batteries in parallel. The grounds will be connected via frame.So when it comes to a choice of a separates, isolator, relay, switch it would really come down to your needs.preference and usage model. It sounds like you have the correct idea with just using a relay to connect the batteries when the van is running. You can connect to the "Run" circuit on the key. When the key is in "run" the batteries will be connected. As Jamie said earlier, you don't really have to worry about power loss when running so, a magnetic latch relay is not a necessity.The only other concern would be the heat of a continuous duty solenoid. If that is not a problem where you plan to install, it will work fine. When looking for a high current solenoid make sure it rated continuous duty, and try to get one with silver alloy contacts,

It then comes down to options, if you only want it come on in run, then wire the "run" to one side of the coil and ground to the other. You might put a switch on the ground, in case you want to disable it for some reason. (located preferably somewhere that wont, get bumped).

Also I do believe you won't have a problem when the solar and the alternator are charging at the same time. I know the two Morningstar specs that I have read said so, but you should check your documentation to make sure. They have more then one 10 amp capable version I did not know which one is yours.

Good luck, have fun.

PS I have a Trombetta 200 amp solenoid, that you can have for shipping charges. It is the solenoid . PM if interested.

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Old 09-05-2012, 03:32 AM   #8
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Re: Solar regulator and alternator sharing ground.

Thanks for the responses, I think I am going to go for a relay disconnect on the alternator. (mostly cause this seems like the cheapest/most reliable option) I hooked up all the solar yesterday and it seems to be charging the house battery alright. I'll be getting some gauges together soon so I can get some idea on how well its charging.

I made up a quick schematic sketch of the circuit, there are probably some errors I overlooked but it is approximation of what I'm doing. Alot of it is already installed, I'm just waiting on a few more components.

"The only other concern would be the heat of a continuous duty solenoid."

If space permits I'll probably try to install it in the engine compartment next to the battery.

"PS I have a Trombetta 200 amp solenoid, that you can have for shipping charges. It is the solenoid . PM if interested."

I will do that, i appreciate the offer!

Thanks again everyone, I've learned alot from this site in the last few weeks! I'll put some pictures up of the build progress once I transfer them to my computer.
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Old 09-05-2012, 08:57 AM   #9
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Re: Solar regulator and alternator sharing ground.

If you're worried about heat consider a Blue Sea magnitic latch relay

IMO it's better anyway...better built, operates better, pulls less load, full manual controls, and is rated for 500 amps. Somewhat expensive though.

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