battery charging

[KokaNostra]

Hello everyone.
If there is a battery up front for a trolling motor, and that battery has a two bank charger. That charger should be able to be hooked up to the motor battery for charging also, yes? I know the alternator charges the back battery, If the charger has two banks why not hook up the other battery just in case?

 

[lowe1648mt]

Battery charger

That's what it's made for. Should cause no problems. Just be shure to check the water in both batts once in a while. Even an automatic charger can boil a battery dry.

 

[Full_Monte]

Welcome to the forum! I have been through this recently with a three-battery system...one in the bow and two in the stern. It's worthwhile, I think, to put in a battery charger that charges all the batteries on board with one plug. I used #12 marine gauge wire I got on eBay. The system makes charging batteries a non-issue for me.

 

[Mav186]

Great question KN (great name too!),
I just spoke to my service dept manager on wed about this very issue. I'm having a 24v I-Pilot system installed in the near future and asked if they could install put a 3-bank charger (instead of a 2-bank) to charge all batteries at one convienent plug. I was told that they advise against it because of the greater distance the main battery has to the chargrer vs. the 2 bow mount batteries. Basically he said the front batteries would be maintained perfectly, but the battery placed all the way in the stern, would not be maintained as well because the charger will be placed so far away (due to cable length and voltage drop). However, this may not be an issue if the cable were to be replaced with thicker gauge??? I don't know...all I do is let the smoke out of every wire I touch!!laugh hyst

 

[MMDON]

Battery charging should never be done on anything less than #8 marine wire and preferably #6 if you are going to run any distance with it. I have a 4 bank charger using 2 banks to charge my 2 front batteries for the 24 volt electric motor and a bank each for the accessory battery and the main. I've run the same blue tops for 6 years now without a problem. My batteries are 16' apart from front to rear on my 21' Tjet. The whole system plugs into a plug on the bow. It shouldn't be a problem if wired correctly.

 

[Full_Monte]

I respectfully disagree with the wire size recommended. The larger the wire, the lower the voltage drop...true...but we're talking about current here. The current carrying capacity of my #12 wire is about 25 amps, but I am charging at 15 amps per battery. So, my wire is up to the task. I run the charger in the bow and run the wires to the two rear batteries independent of each other. The MK instructions say to use this size wire, so anything larger is an expensive overkill IMO. The current-carrying capacity of wires of various types can be found online or in any wiring manual.

 

[MMDON]

You are correct. MinnKota specs 14AWG 6'

My bad. I do see some of that smaller wire melting when there are problems as posted on other boards . . .

 

[Full_Monte]

I found it interesting when I installed my MK345 charger (22lbs), that the wires coming out of the charger were #14 gage, and had an inline 30 amp fuse on BOTH the positive and negative wires. While I didn't change the fuses to a lower value, I think the ampacity of the 14ga. wire is about 15-20 amps, so a 30 amp fuse seems dangerous to me. If anyone can explain this to me, I'd appreciate it.

 

[skookum9]

The 30amp fuses should be of no danger at all. They are there to protect the equipment, not the conductors. The conductors are sized to fit the maximum anticipated current draw, although probably lighter than I personally would choose should it be something I were to build. You could certainly reduce the size of the fuses that are inline but you may find that this might incline the system to burn your fuses at a much higher rate. These fuses were probably selected by the manufacturer to avoid something I refer to as nuisance tripping. Those lighter conductors can handle a higher amperage for a short duration and if the unit ever exceeded the desired amperage, it would likely go enough beyond to fry those fuses quickly. I probably wouldn't worry about the 30amp fuses but if I were to change them out, I doubt that I would go any lighter than 20amp to replace them with.

Typical wire to ampacity sizing is as follows,
14ga = 15amp
12ga = 20amp
10ga = 30amp

There are exceptions to these standards but this is the general rule of thumb as per the National Electrical Code.

 

[Full_Monte]

Great question KN (great name too!),
I just spoke to my service dept manager on wed about this very issue. I'm having a 24v I-Pilot system installed in the near future and asked if they could install put a 3-bank charger (instead of a 2-bank) to charge all batteries at one convienent plug. I was told that they advise against it because of the greater distance the main battery has to the chargrer vs. the 2 bow mount batteries. Basically he said the front batteries would be maintained perfectly, but the battery placed all the way in the stern, would not be maintained as well because the charger will be placed so far away (due to cable length and voltage drop). However, this may not be an issue if the cable were to be replaced with thicker gauge??? I don't know...all I do is let the smoke out of every wire I touch!!laugh hyst

That service dept. manager should look for another job as he is totally unknowledgeable about the one he has now.

 

[skookum9]

Actually, voltage drop is a serious concern, especially when talking about DC voltage. I would still expect the charger to be sufficient to charge all three batteries without fail, as long as the conductors were sized right. If voltage drop is ignored, the results can be damaged conductors, damaged batteries, damaged charger and can even result in an electrical fire that could consume the boat and whatever shelter it is parked inside of. I'm not sure what makes you think this is an unreasonable concern.

 

[Full_Monte]

I think it's an unreasonable concern because the instructions enclosed with battery chargers discuss the remote wiring of batteries on the boat and how it should be done. Admittedly, there are some caveats, and the instructions cover these. With all the multiple bank chargers being sold, many are being installed with extendable leads for bow-and-stern batteries. I find it difficult to believe that many battery chargers are being sold that cannot be used in the bow-and-stern applications common in fishing boats. I find it odd that a service person would have the opinion that it won't work when people are installing these things every day.

 

[skookum9]

As long as the conductors are adequate for the job, there should be nothing wrong with installing a system like this. Not having seen the vessel in question or the equipment the tech was confronted with, I cannot know what the circumstances were. But voltage drop is real and can have adverse effects. I would expect the owners manual for the equipment to have a recommended maximum distance per conductor size advisory, and I would try to follow this. Just my thoughts.

 

[knotatwork]

The 30amp fuses should be of no danger at all. They are there to protect the equipment, not the conductors. The conductors are sized to fit the maximum anticipated current draw, although probably lighter than I personally would choose should it be something I were to build. You could certainly reduce the size of the fuses that are inline but you may find that this might incline the system to burn your fuses at a much higher rate. These fuses were probably selected by the manufacturer to avoid something I refer to as nuisance tripping. Those lighter conductors can handle a higher amperage for a short duration and if the unit ever exceeded the desired amperage, it would likely go enough beyond to fry those fuses quickly. I probably wouldn't worry about the 30amp fuses but if I were to change them out, I doubt that I would go any lighter than 20amp to replace them with.

Typical wire to ampacity sizing is as follows,
14ga = 15amp
12ga = 20amp
10ga = 30amp

There are exceptions to these standards but this is the general rule of thumb as per the National Electrical Code.

I know of those ratings to be in a conduit or raceway laying in free air they have a much higher value

 

[skookum9]

I'd like to know what your source is on that increase in value when in free air. As I said, there are some exceptions, but I've never heard of anything about free air wiring changing their ampacity. I'd strongly recommend the standards published in the National Electrical Code. Those standards are recommended as a MINIMUM standard. They are given to keep people from getting themselves into trouble. If it's your boat then I guess it's your option but understand that you are taking unnecessary risks to your equipment. Not to mention, in some cases such as being off shore, risking even your life. If you indeed do have a source for the information about free air changing the ampacity of wire, please post it so I can know where to search it out. I'm sure my inspectors would love to learn about it, and I know I would.

 

[650cent]

NEC table 310.15(B)(17) gives ampacity of single conductors in free air, but I don't think I would apply it to boat wiring.

Bill

 

[SuperD]

My understanding of the smart battery chargers is that they shut themselves off when the resistance and heat get to a certain point because the charger believes the battery if fully charged. Using small wire for long runs gives the charger false signals and you won't get good charges. I'm just say'in.

 

[skookum9]

Bill,
Unfortunately, I left my '08 code book at work and haven't yet ordered my '11 book, so I'm going to have to wait until Monday to be certain but I think the code reference is superceded by another code. First, the code book I checked on tonight is an old one and is not accurate but what I found was this. It is tables 310-17, and 310-19 that both reference free air specs but with a note implied by an asterisk. This note sends one to 240.3, which while in reference to OCP, clearly specs these smaller wires to the standard accepted amerages. Not that it really matters because as you said, not a good idea in this case anyway. And as SuperD accurately points out, it will likely cause charging system issues. I do thank you for a good code book chase, the practice always does me good.

 

[Mav186]

My understanding of the smart battery chargers is that they shut themselves off when the resistance and heat get to a certain point because the charger believes the battery if fully charged. Using small wire for long runs gives the charger false signals and you won't get good charges. I'm just say'in.

Thanks Sup D...That was exactly what my Service manager was talking about too. The fact that false signals back to the charger would not properly maintain the rear batteries to the same degree of the bow batts. The leads are specifically calibrated based on the length of the leads...any modification to these leads can result in false signals and improperly maintained batts. The bank chargers I was looking to purchase did not have long enough leads to run to the stern. I had a pair of 2 bank chargers installed...a 5 amp trickle charger for the main and spare batts in the stern, and a 10 amp for the bow batts for the 24v bow mounted electric motor. The lay-out is very convienent and is working out very nicely. tooexcited

 

[SilverFox]

One thing not being mentioned here is the difference between house wiring and marine. What the NEC says about AC conductors is one thing, and what ABYC (Amercian Boat and Yacht Council) is another. It's an apples and oranges comparison.

Here's a link to a good read and some nice charts for marine grade wire ampacity - http://www.boatus.com/boattech/cable.htm

I have to agree with the issue of extending charging leads, especially with different lengths involved. This is far more critical in a 12vdc circuit. I would not install batteries any further than the leads allow unless the charger mfr states it can be done, and even then, only if all batteries attached to that charger are at the same relative distance away.

Mav you did it right, and that's exactly how I'd have approached the same problem. In my case, the my bow mount is powered by a pair of batteries in the stern via the factory wired plug in the bow. This is one area I will be upgrading in the future, replacing the factory run 10awg with 6awg since I'm running a 75# thrust trolling motor up there.