Adding a second battery

[dahlke]

Obelix and I are almost ready to go cruising Looking forward to uploading a lot of cruising images and "log entries" There is just one little project to finish first. Adding a second battery with a separating relay (correct term?). My motor is the original MD6A with a generator AND dynastart. There are currently 3 thick cables on my one battery. I believe one (+) goes the generator and one (+) to the dynastart the third cable is "ground" (-).

I've tried to clean up the original wiring a bit (not done yet). The box on the right (green) in the below image is all the items that should be supplied from the house battery (lights, GPS, music and so on). The box on the left (blue) is everything related to the motor (electric diesel pump and instruments). Right now the "+" to both boxes comes from the generator. It was this way before I started messing about. Isn't that odd? Wouldn't a "+" directly from the battery be a more reliable option?

As I would like to add another battery and "separate" the two using a separating relay am I correct in thinking that I need to add a new "+" and connect this one directly to the box on the right (green)? What about ground (-)? Do I need to add a new ground (-) cable?

There is no "main fuse" in the system would adding one be a good choice?

Image from the manual (of the separating relay)

Skærmbillede 2014-06-02 kl. 18.16.10.png (46.45 KiB) Viewed 55841 times

http://www.biltema.dk/BiltemaDocuments/ ... 30_man.pdf

[prjacobs]

I don't know if this is of any help, but I'll tell you what I did:
2 batteries connected to a battery switch, allowing choices of #1, #2, both, or off.
1 set of leads from the battery switch "out" directly to the engine (#4 cable as they are very short)
1 set of leads from the battery switch "out" directly to the 2 fuse panels (#10 wire.)
Solar panel charge controller that keeps the batteries isolated from each other.

This allows one source of current to the engine and the fuse panel, with the ability to select either or both batteries. I usually leave the switch on "Both" unless I'm anchored, then I'll switch to one battery to keep the other in reserve for starting the engine. When running the engine I have to remember to put the switch back to "Both". And when I leave the boat the switch is off, giving great peace of mind to the guy who did his own wiring

[dahlke]

Thanks Peter My memory being what it is I would differently forget to flip that switch to "both"

This is what I'm planing to do. I'm 90% sure it's correct - fingers crossed

I would like to be able to keep an eye on my power consumption so I'm adding a Nasa BM1 (http://www.nasamarine.com/proddetail.ph ... -1_Battery).

Obelix_electric_with_BM1.png (17.85 KiB) Viewed 55834 times

[Sanlen]

Mads,

I see som problems with your drawing:

• 1. The negativ lead from the starter battery to Nasa BM-1 is of no use - the BM-1 is only for one battery bank.
  2. The solution requires that the charging function of the Dynastart has been disabled - it can easily be done at the big relay in your first picture. I did this on my old MD6 and it worked fine. Otherwise you can connect the alternator directly to the house battery and skip the relay if you keep the charging function of the Dynastart (not recommended as it gets warm and wears out).
  3. Your drawing lacks a main switch to the house battery.
  4. In general it is better to have the main switches on positive leads.

[dahlke]

Thanks for your comments Jan - I appreciate it very much I'm quite the novice when it comes to this sort of stuff

1. Maybe I have misunderstood the manual (the two images below is from the manual http://www.nasamarine.com/images/file/BM1+-BM2+.pdf). I was trying to follow the directions in the second image. If I can only monitor one battery I would prefer to monitor the house battery. What do you recommend I do?






2. Sorry if this is a stupid question Why would the charging function of the Dynastart need to be disabled? How did you disable the charging function yours while still keeping the starter function?

3. Ups, you are 100% correct I will be sure to add another switch or perhaps one of those "fancy" on/off/combine switches (http://www.bluesea.com/products/6011/m- ... itch_-_Red)

4. Another question that may fall into the "stupid question" category Why is it better to have the main switches on the positive leads?

[Sanlen]

Thanks for your comments Jan - I appreciate it very much I'm quite the novice when it comes to this sort of stuff

I've learned the hard way (and I hopefully remember some from school)

1. Maybe I have misunderstood the manual (the two images below is from the manual http://www.nasamarine.com/images/file/BM1+-BM2+.pdf). I was trying to follow the directions in the second image. If I can only monitor one battery I would prefer to monitor the house battery. What do you recommend I do?

If your monitor is a BM-1 and not a BM-2 you should follow image one. Positive lead should connect to your charging relay (and electrical panel), negative lead to the engine (and electric panel). I would recommend that you install a main switch on the positive lead between the battery and the electrical panel.

2. Sorry if this is a stupid question Why would the charging function of the Dynastart need to be disabled? How did you disable the charging function yours while still keeping the starter function?

No questions are stupid The two charging systems will interfere and probably cause problems. SInce the Dynastart has a very week alternator it is better to disable that function. The Dynastarts are also prone to overheat when they are acting as a alternator. You disable the charging by removing the lead that connects "DF" on the charging relay with "DF" on the Dynastart.

3. Ups, you are 100% correct I will be sure to add another switch or perhaps one of those "fancy" on/off/combine switches (http://www.bluesea.com/products/6011/m- ... itch_-_Red)

I personally prefer separate switches - my experience is that the combined ones tend to fail over time.

4. Another question that may fall into the "stupid question" category Why is it better to have the main switches on the positive leads?

I have learned that it is better since the engine acts as ground point and you also use ground points in your electrical system (negative bridges) - then the risk for short circuits is minimized if you switch off the positive lead. It is also better in terms of galvanic corrosion - if you or your boat neighbour have powerleaks into the water then your throughhull fittings and other parts are less affected. Maybe someone with more electrical knowledge can explain this better

[dahlke]

Thanks for your comments Jan - I appreciate it very much I'm quite the novice when it comes to this sort of stuff

I've learned the hard way (and I hopefully remember some from school)

Ugh, that sounds expensive

1. Maybe I have misunderstood the manual (the two images below is from the manual http://www.nasamarine.com/images/file/BM1+-BM2+.pdf). I was trying to follow the directions in the second image. If I can only monitor one battery I would prefer to monitor the house battery. What do you recommend I do?

If your monitor is a BM-1 and not a BM-2 you should follow image one. Positive lead should connect to your charging relay (and electrical panel), negative lead to the engine (and electric panel). I would recommend that you install a main switch on the positive lead between the battery and the electrical panel.

Thanks I must have missed that in the manual.

2. Sorry if this is a stupid question Why would the charging function of the Dynastart need to be disabled? How did you disable the charging function yours while still keeping the starter function?

No questions are stupid The two charging systems will interfere and probably cause problems. SInce the Dynastart has a very week alternator it is better to disable that function. The Dynastarts are also prone to overheat when they are acting as a alternator. You disable the charging by removing the lead that connects "DF" on the charging relay with "DF" on the Dynastart.

If I understand you correctly I simply need to disconnect one wire. I found the "DF" mark on the charging relay and found the other end of the wire on the Dynastart using a mulitmeter. The wire has been disconnected in both ends. Is that relay all I need to do? You weren't kidding when you said it was easy

3. Ups, you are 100% correct I will be sure to add another switch or perhaps one of those "fancy" on/off/combine switches (http://www.bluesea.com/products/6011/m- ... itch_-_Red)

I personally prefer separate switches - my experience is that the combined ones tend to fail over time.

Is there a specific kind/brand of switch (separate) you would recommend?

4. Another question that may fall into the "stupid question" category Why is it better to have the main switches on the positive leads?

I have learned that it is better since the engine acts as ground point and you also use ground points in your electrical system (negative bridges) - then the risk for short circuits is minimized if you switch off the positive lead. It is also better in terms of galvanic corrosion - if you or your boat neighbour have powerleaks into the water then your throughhull fittings and other parts are less affected. Maybe someone with more electrical knowledge can explain this better

Thanks, I will move my switch to the positive leads

[Bob McGovern]

Jan: So it is okay to disconnect the Dynastart's battery charging lead & use the DS as a pure starter? That won't burn up the voltage regulator (or maybe it doesn't have a voltage regulator)? Cuz you aren't supposed to run an alternator w/out a load; that will generally kill it fast. (That's why you always stop the engine with the fuel cutoff BEFORE turning off the ignition key, & never turn a battery main switch to OFF while the engine is running.) If yes, that is really useful information, cuz I've been leery of the Dynastart as a battery charger since learning of it. There's good reason automobiles don't use magneto generators/dynamos any more.

Mads: AC and DC power are not quite the same, but they are similar enuf in this regard. At some point (with AC, only one place in the entire system), the neutral or negative wire or battery post is lead to earth (ground). This can be via the motor/prop shaft, metal thru hulls, grounding plates, or a copper rod pounded into your garden 2m deep. Thus, the electrical potential between neutral/NEG and local environment is held at zero -- no spark will jump between them, and if you hold a neutral wire in one hand, no current will pass thru your body.

Therefore, all the electrical potential exists between the hot/POSITIVE leg and the neutral/NEG/ground/water. It's that downhill flow you want/need to interrupt. That's why your switches and fuses go on the hot/POS side. Generally as close to the battery as can be.

[dahlke]

Seeing as I can't go sailing (waiting for my "new" headsail) I've been scouring the internet for anything related to dynastarters in order to get a basic understanding of how they work I haven't succeeded yet but by coincidence I came across a thread about disabling the charging part of a dynastart (http://www.ybw.com/forums/archive/index ... 64126.html)

"You can safely disconnect the DF and D+ connections and use it simply as a starter. There's no solid state stuff inside to get damaged as there is in the Alternator"

Though I would post it here for the benefit of anyone reading thru this at some point in the future

[dahlke]

I've updated my little drawing (moved the main switches). This looks correct, right? One switch on the lead to the starter (formerly known as dynastarter ) and one on the lead to all the household loads.

Turns out the Nasa BM1 if wired according to figure 2 (earlier in this thread) can actually display the voltage of the starter battery (press V&A button). As Jan mentioned above the BM1 can only monitor ONE battery but the current version of the BM1 (the older version(s) didn't have this feature) is apparently also able to display the voltage of the starter battery (and only the voltage - nothing fancy).