This illustration will better show how to connect charger sources and loads. Connect "across" the bank and it will cause the batteries to charge & discharge more evenly and uniformly.
This is the recommended diagram by every battery manufacturer I know of from Trojan, Lifeline, Deka/East Penn, Odyssey to Rolls Battery and just about everyone in-between.
Parallel Batteries - Incorrect Wiring
I have used my battery tester many times in scenarios like this and in every example I see the bank unevenly balanced and the batteries show it under testing. I have a battery tester than can show me the differences in a bank of batteries wired like this, and it does matter. Do not just connect your charge sources or loads to one end of a bank.
But, you don't need to take my word for it this is what Odyssey Battery (EnerSys) has to say about properly connecting batteries in parallel:
QUOTE = ODYSSEY BATTERY
"Typically the positive and negative leads to the load are taken from the same battery; usually the leads from the first battery are used. This is not a good practice. Instead, a better technique to connect the load is to take the positive lead from one end of the pack (the first or last battery) and the negative lead from the other end of the pack."
Negative DC Wiring
The bottom negative wire on that buss bar is for the battery charger. If your boat is equipped with a battery monitor the chargers DC negative wire should be placed on the "load" side of the monitors shunt as is shown here.
As always the DC negative wire should be the same size as the DC positive wire. Using a DC negative buss bar is an easy way to keep the battery posts clean and free of clutter.
Wire The Temp Sensor & AC Wiring
In this photo I have plugged in the temp sensor and am testing the charger to see if it recognizes the temp sensor. It did. With the Sterling Remote Panel the charger will tell you the battery, charger and transformer temp to within 1 degree. A pretty cool feature.
The AC wiring should be sized based on the manual for your charger. For this charger it calls for 14/3 AWG AC colored wire. The input for the AC wiring is marked L - N - G or BLACK/HOT, NEUTRAL/WHITE & GREEN/EARTHING GROUND.
Your charger should ideally have it's own dedicated breaker in the AC panel sized to protect the AC wire you're using. It is not suggested to share a breaker with any other device for a fixed mounted charger. This one uses a 15A breaker and 14/3 AWG AC color coded wire.
Always install your AC & DC wiring to acceptable color code standards. For AC and a single phase charger like this it is:
Black = HOT
White = NEUTRAL
Green = GROUNDING/EARTH
Red = POSITIVE
Black or Yellow = NEGATIVE
Green = BONDING or EARTHING
It is not advised to run AC & DC wires together in the same bundle unless sheathed separately. Try to keep your AC/DC wiring runs separate or sheath the AC wires to keep them isolated from the DC wiring.
Wiring Up The DC Side
In this picture I have mounted the charger to a back board which will get mounted to the boat. The wires are affixed to the board with sufficient strain relief to prevent inadvertent loading of the attachment point to the charger. The ends of the wires are crimped with ring terminals using the proper tool and then sealed with adhesive lined heat shrink. I also coat the lugs with a terminal grease to prevent oxidation/corrosion at the lug/terminal strip interface.
One of the more critical aspects of charger installations, that I nearly always see violated, is the green case/chassis ground wire shown. If I had to guess I would say that nearly 85% of the installations I see are either not case grounded or the case ground wire is to small.
This green grounding wire grounds the chargers metal frame to the vessel and allows your over current protection devices to work properly, if there is an internal fault that shorts to the case.
Chargers and inverter/chargers are equipped with grounding connections for both the AC
side and DC side of the device. Proper Earthing is there to prevent shocks from the AC side, and to minimize or prevent fire hazard from DC side.
About eight times out of ten the AC Earth connection is the only one I see being used. So, what if there were a fault in the DC side of the system? Can the AC ground wire handle that? The answer to that question is almost always a resounding NO!
A fault in the DC side can supply enough current to overwhelm and overheat the AC green grounding wire. It can even do this well before tripping a fuse or breaker. It is a must do requirement that the case be bonded/grounded/Earthed with a green wire of not less than one size smaller than the DC conductors!!
This green wire gets sized for the DC side of the charger. The green AC ground will not satisfy the ABYC case ground requirement on an AC/DC battery charger. Follow me on this one. If there is a fault on the DC side of the charger the AC green wires size may not be able to handle this fault and could be undersized in having to handle that fault. This is why the requirement for the chargers case ground is for no less than one size smaller than the DC output wires.
The ABYC standard suggests that the case ground for chargers needs to be no less than one AWG gauge size smaller than the DC output wires. So, if you have 6 GA DC wire then you need no less than an 8 GA case ground wire. Even if your wire is already technically "over sized" your surveyor or insurance company may not know this so it is always best to wire it equal to or no less than one AWG size less than the DC output wires.
This green wire is routed from the charger to the ships DC ground buss which normally is earthed or grounded to the engine block..
Test & Program Your Charger
It is always a good idea to check with your battery manufacturer and obtain the recommended ABSORPTION, FLOAT and EQUALIZATION voltages. You will then program your charger to your batteries using the preset charge algorithms. Some chargers offer very little in the way of "smart" charge programs, sometimes four or less, and others, like this Sterling, offer plenty of options. As mentioned the Sterling PCU chargers also offer a user defined program that you can self program. Very cool for those applications that need it.
You can always choose to use GEL or AGM settings on wet cell batteries but a good quality charger will not go into equalization mode, and should not, while in AGM or GEL mode. If charging WET batteries with a GEL or AGM program you'd need to switch back to a WET program to equalize your batteries. In contrast you should NOT use AGM or WET settings on GEL batteries.
Just a note on equalization. Sulfation is like cancer of the battery, once it has set in it is only a matter if time before the battery passes on to battery heaven. Equalization is like Chemotherapy. It helps prolong the life but only prolongs the inevitable for some time. DO NOT over equalize your batteries as it can cause plate decay and lead to shorter life if over done. The best thing you can do for your batteries is keep them at or near 100% state of charge as often as possible. If on a mooring this will require wind or solar as an alternator simply won't do this and the batteries will sulfate prematurely.
I much prefer to equalize batteries ONE AT A TIME and monitor the progress with a hydrometer or, what I use, a sight refractometer. A good charger with temp sensor should monitor the temp but it never hurts to have a digital infrared thermometer on hand while equalizing. Please DO NOT equalize batteries unattended! It is very wise to be there during equalization. If you are unfamiliar with equalization PLEASE research this before hitting the button. To equalize one at a time simply disconnect the batteries not being equalized.
Thoroughly test your charger before leaving it to do it's thing. I personally don't like "unattended" charging even with the best built chargers in the world. This is just MY personal preference, so consider it, but don't take it as gospel. For unattended charging I use solar. It works for us, but may not for you.
Unfortunately for many boaters in warmer climates, with WET cell batteries, the ambient temps require that chargers be left on and most often "unattended". This is due to the exacerbation of battery self discharge in warmer temperatures. Heat kills batteries, cold helps prolong life.
Sulfation and self discharge greatly accelerate the warmer battery temps are, so do keep your batteries topped up as often as you can. In a perfect world all chargers would perform flawlessly for 20+ years. Sadly for the boating public we don't live in a perfect world and many a charger has taken out a perfectly good bank when it decided to pack it in, I see it OFTEN. When owners leave a charger on constantly when the charger fails it often takes the batteries out with it. This simple charger failure now becomes an entire new bank and a new charger as opposed to just a charger. If you don't need your charger on constantly consider NOT leaving it on and unattended, if you don't absolutely need to. Balancing unattended charging & its potentials for failure modes, versus the potential for self discharge and the resulting sulfation is one you'll have to tackle on your own.
Good luck with your installation!!
After numerous requests from readers, who were wishing to support this site through the purchase of a charger, I have now worked with Sterling Power USA to add the Sterling ProCharge Ultra chargers to the site.
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