Choosing A Charger
*For this article we are installing a: Sterling ProCharge Ultra Battery Charger
*The information in this article, other than specific to the Sterling ProCharge Ultra, can generically apply to all marine battery chargers. Key words here being “marine battery chargers“.
How Do I Size A Charger?
Adding A Remote Display
Just Say NO to Dip Switch Chargers
In today’s day and age there is less than zero excuse for a marine battery charger manufacturer to not offer more than three settings. Typical of far too many chargers all you get is three settings FLOODED, AGM & GEL.
Unfortunately the voltage behind the words are very often not appropriate for your batteries. Dip Switch chargers, or as I often refer to them as “Dip Shit” chargers are an extremely poor choice in today’s market where recommended battery voltages are all over the map. Dip Switch chargers also very often lack temperature compensation. If your battery charges at 14.8V at 80F it CAN NOT charge at 14.8V at 100F!!
Battery Type is very often an Irrelevant Setting!
“RC, clearly now, you’re just a big freaking lunatic?”
I know that statement seems bold but please focus on what I am going to explain. What is relevant to your batteries are the battery manufacturers recommended absorption and float voltages.
As a boat owner, and battery manager, you need to stop looking at the words on a chargers pre-set Dip Switch list and instead look at the VOLTAGES behind the words.
AGM, GEL, Flooded, FDC etc. are words, and they mean absolutely nothing without knowing the VOLTAGES those words represent. One manufactures voltage for AGM will not always be the same as the next. For this reason you should only focus on the VOLTAGES the words represent. If the charger maker does not tell you the voltages, that the words FLOODED, AGM or GEL represent, WALK AWAY!
For some AGM batteries you will be much better served using the FLOODED setting rather than the AGM setting and vice-versa. Your batteries DO NOT charge by words they charge based on VOLTAGE. A charger should always be chosen to match your battery manufacturers recommended charging voltages. A charger offering a full user defined custom setting will always be able to match the manufacturers recommended absorption & float voltages where a charger with just two or three choices very often will not. If your charger can match the battery then battery life and performance will suffer.
VOLTAGE is the key, not the words.
Ignore the WORDS and focus on the VOLTAGES
Just take a big red marker and cross out the Battery Types. Now that you’ve done that, find the voltage settings that match your batteries. Even with 11 pre-sets to choose from how well did you do..? Now imagine you only had two or three settings?
Let’s choose a charge profile for Lifeline AGM Batteries:
Manufacturer suggested charging voltages:
AGM Batteries – Which “AGM” Preset works?
Lifeline AGM’s = 14.4V & 13.4V = AGM Preset #1
Odyssey TPPL AGM’s = 14.7V & 13.6V = Neither AGM Preset
Firefly AGM = 14.4V & 13.2V = Neither AGM Preset
Mastervolt AGM = 14.4V & 13.2V = Neither AGM Preset
Full River AGM = 14.7V & 13.7V = Neither AGM Preset
Rolls AGM = 14.7V & 13.7V = Neither AGM Preset
East Penn/Deka = 14.6V & 13.6V = Neither AGM Preset
US Battery AGM = 14.4V & 13.4V = AGM Preset #1
Trojan AGM = 14.4V & 13.5V = Neither AGM Preset
This list, of manufacturer suggested voltage guidance, is why you should always buy chargers that have a custom setting. Even with 11 pre-sets only 1 out of 9 “AGM Pre-Sets” work for the Lifeline AGM’s. Once again please do not focus not on the words, but rather on the voltages.
Which flooded preset works for Trojan or Deka flooded batteries?
Trojan Flooded = 14.8V & 13.5V = Neither Flooded Preset is Idea
Deka Flooded = 14.7V & 13.8V = Neither Flooded Preset is Ideal
What do all these batteries have in common? They all ideally need a user customization voltage profile.
Just say NO to dip-switch chargers…
11 Pre-Sets and One User Programmable Charge Profile
The Sterling PCU packs a lot of features into this small form factor charger. Right out of the box it has 11 preset charging profiles. On top of the 11 presets it also has one custom profile that can be tailored for a battery not already met by the preset options.
There are very few battery chargers, at any price, that currently allow the user to build their own charging parameters. A very cool feature for those who may need it, like the owners of Lifeline batteries.
As an example Lifeline battery, the AGM battery manufacturer, wants to see 15.5V, temp compensated, for 8 hours to “condition” (equalize/desulfate) their batteries. Many other competitors chargers have an equalization setting of 16 volts for 1 hour or 16 volts for 4 hours or 15.5 volts for an hour etc. etc.. With the Sterling Pro Charge Ultra you can custom build a “conditioning” cycle that matches the Lifeline battery manufacturer suggestions or any other manufacturers suggestions if not already covered by the 11 preset. All equalization charges should be TEMP COMPENSATED so be sure your charger has a temp sensor if you’re going to be equalizing.
If you click the photo to make it larger you’ll see the 11 presets, and their voltages, plus the custom user profile.
Just Say NO to Egg-Timer Chargers
Seems like we’re saying no to a lot of things, and with good reason. First, let me state the obvious.
The ideal charge algorithm, for marine battery chargers, has not yet been implemented
In order to have an ideal recharge the charger really needs to know what is a house load and what is going to the battery. Seeing as battery chargers only know output current, or more accurately the percentage of its power supply being used, as well as voltage, they can’t have any idea what is flowing into the battery and what is flowing to house loads. This makes implementing a voltage only algorithm difficult at best. Some chargers use smarter algorithms and some use fairly dumb egg-timer type algorithms.
The Sterling ProCharge Ultra uses a number of factors to adjust and adapt the duration of the absorption cycle to what it believes the battery needs. In terms of charge algorithms it works pretty well. A simple explanation is that the ProCharge Ultra examines the duration spent in bulk and can then add or subtract time spent in the absorption stage. This type of algorithm is certainly smarter than a simple egg-timer. While not perfect, it does a better job at keeping the batteries healthy than do many egg-timer based chargers.
In an ideal recharge a battery charger would not drop to float voltage until the battery bank had attained the 99.5% to 100% SOC point. Almost all battery chargers out there, for marine use, drop to float before the battery bank has attained 100% SOC. While this makes them “safe“, for the manufacturers lawyers, it also means that in order to get back to 100% SOC it just takes a bit longer. At a dock this is not a huge deal, if we are getting into the mid to upper 90’s before the float transition. Once the charger drops to float this dramatically extends the time it takes to get to 100% SOC. The absorption cycle is perhaps the most important stage of charging and if it is too short, due to an egg-timer, the batteries can become chronically under charged and suffer the effects of sulfation.
Unfortunately far too many chargers out there work on the simple “egg-timer” principal. Here’s how an egg-timer charger usually works.
- Battery Charges In Bulk Stage Increasing Bank Voltage
- Battery Bank Attains Absorption Voltage Limit
- Once Absorption Voltage Limit is Attained a Fixed Timer Starts
- When Egg-Timer Ends the Charger Drops to Float
What if the batteries were already full when you booted the charger up and it now has a 4 hour egg-timer to burn through?
What if you began charging at 50% SOC and only gave the batteries a 1 hour absorption cycle? Even the best AGM batteries still require well over 3 hours of absorption charging, under ideal conditions, to get anywhere near 100% SOC from 50% SOC, even when being changed at rates as high as 40% of Ah capacity or 40A for a 100Ah battery.
What if the batteries are 50% discharged and it takes 5+ hours in absorption to attain 98-99% SOC and your charger has a 1 hour egg-timer?
One manufacturer even uses this egg-timer algorithm:
- Battery Charger is Turned On
- Four Hours Later the Charger Drops to Float Regardless of SOC
Oh and they call this “smart”..
Egg-timer algorithms are not smart, and in many cases can be unhealthy to batteries. Egg-timer chargers are the lowest form of “smart” you can actually get.
This 20A charger comes standard with three outputs which can be fed to three different banks. The output is distributed by demand not divided equally as some chargers are. So if a start battery was at 99% state of charge and your house bank was at 60% state of charge the house bank will be seeing the vast majority of the charging current and the starter would be seeing 1-2A or less.
For owners who have a charge distribution system in place, such as an Echo Charger, Duo Charger, VSR (voltage sensitive combining relay), or in the US often referred to as an ACR (Automatic Combining Relay), the outputs can be “jumped” together as shown to create a simple “single output” charger.
Technically with this charger you don’t need to “jump” the unused outputs if using it as a single output charger. The US distributor feels, and I agree, that it is a wise idea to equally load the output FET’s so I chose to jumper than to even load the outputs. The two red jumpers are jumping output 1, 2 & 3 to load all the output FET’s equally. This essentially makes the charger a single output 20A charger rather than a three output 20A charger. All current in this installation will feed to the house bank and the starting bank will be charged via a Blue Sea Systems ACR relay. You would do the same with an Echo or Duo Charger.
This particular boat has an ACR / Automatic Combining Relay so the charger is being used as a single output. Keep in mind that nearly all chargers, with the exception of some very expensive ones, still only have ONE output setting, in terms of charge profile, so dividing it up is not really necessary unless you don’t have an ACR, Echo Charger or Duo Charger type of battery bank charge distribution.
Also note the location of the green fuse. This is the charger output fuse and it well located and easy to change if necessary.
The two heat shrink ring terminals are just illustrating where you can connect the neg and positive battery leads to.
It should be noted that on 30A and larger Sterling Pro-Charge Ultra chargers they use large studs as opposed to a small terminal strip for the DC output. I really wish the 20A model had these studs too but it does not. For that reason alone I would suggest considering the 30A or larger model if you can.
Choose A Location & DC Wire Sizing
The location your charger is mounted in plays a critical role in its life span & longevity. Care should be taken to follow your manufacturers instructions of orientation, access to air, moisture or battery gas exposure.
1- Mount the charger in a location were it can run cool and air can move around it. An engine space is often a poor location because the engines, and engine bay, remain warm long after the engine has been shut down. Many also have water heaters that can keep the temps in these small areas higher than average. While on many vessels you don’t have a choice in this matter, due to space constraints, always look for a location outside the engine space before installing there. If the charger has a fan be sure to mount the inlet and outlet in areas where they will have unobstructed air flow. If necessary, or prudent for your charger, you can cut ventilation holes in lockers, and then cover the holes with pre-made ventilation grills to allow air flow. Ventilation for your charger does not have to look bad. There are many grill options available from teak to stainless steel.
2- If your hull is a dark color it is best to avoid mounting the charger directly to the inside of the hull. Topside hull temps, in direct sun, with dark colors, can easily exceed 140F! I have one customer who’s AGM’s were dead every two seasons use, about 100 cycles, like clock work. He had done everything suggested by the manufacturer including installing solar for his mooring sailed boat to keep them at or near full charge. It was not until I measured the battery compartment temps at 133F, located behind the cabin settee seat back, that we figured out his failure mode. Just as heat is bad for batteries it is also bad for the charger. A cool running charger is a happy charger. If your chargers fan runs constantly it may be trying to tell you something..
3- Battery chargers should not be mounted in a battery compartment/space despite being ignition protected. Corrosive battery gas can damage the metals in the charger and lead to shorter life or corrosive damage. All lead acid batteries, WET, GEL and AGM have the potential to vent corrosive gas. Just because your battery is a VRLA design does not mean it won’t vent corrosive gas if over temped or over charged. A battery compartment is an absolute last resort location for a charger.
4- Try to find a location that is dry and will not have the possibility of water dripping on the charger. If there’s even a slight potential of water exposure a drip shield should be constructed to protect the charger. The drip shield should prevent water from damaging the charger, but also allow for proper cooling. This is not always an easy task so mounting in a known dry spot is always the best approach. Generally speaking, higher in the boat is often better than lower in the boat for a charger mounting location. Areas closer to the bilge, or with direct ambient access to the moist bilge air, tend to be more humid and corrosive environments.
5- Try to mount the charger as close to the battery bank/banks as possible without mounting in the battery or engine compartment. Shorter wire runs mean less installation cost, less voltage drop can make for better charger performance over the long haul.
6- The area on your vessel where the charger is mounted should be clean and free of oils, vapors or other sorts of contamination. While UL 1236/ABYC chargers are “ignition protected” it is not recommend to install them where any gas vapor can accumulate. This includes LPG, gasoline, hydrogen gas or where stored solvents could spill & leak.
The DC wiring is a very critical part of a chargers performance. Most manufacturers want to see a maximum voltage drop of between 1% & 3%. Voltage drop is determined by the amperage flowing through the cable over the round-trip length of the circuit. This means you add the full length of the negative and positive wires, plus the max amperage that will flow, to determine your voltage drop.
This 20A charger was wired up for less than a 1% voltage drop using 6GA wire. I personally prefer as little drop as possible. Realistically I could have easily wired this with 10GA wire and been at 2.75% voltage drop but Sterling ideally wants to see less than that and I don’t always stock 8GA wire, so 6GA it was.
A 3% voltage drop at 14.6V is roughly 0.44A of lost voltage between the charger and battery bank. This can potentially leave you with a charging voltage at the battery of just 14.14V. With DC charging sources bigger wire is almost always better.
Just say YES to On Battery Temp Sensing
This is the Sterling ProCharge Ultra’s on battery temp sensor. The supplied sensor is 10′ long, but it can easily be extended with a typical 6P2C male to female RJ11 phone cable or with an RJ11 in-line coupler.
The sensor is using the two middle terminals as would the typical red & green two wire phone cord. Here’s a hint though, if you need to extend the temp sensor you’re likely going to need much larger gauge positive and negative output cables. Try to keep the charger as close to the batteries as you can without physically being in the same compartment.
Temperature sensing of your batteries is very important to the longevity of a bank, especially with valve regulated lead acid batteries such as AGM, TPPL AGM or GEL. The hotter the climate you are in the more important temperature compensation is. Temperature compensation is more critical as temperatures rise rather than fall but both are important. As the battery temperature goes up, the battery charging voltage must come down. As battery temperatures drop the charging voltage can go up.
STORAGE WARNING: For batteries in long term winter storage, in colder climates, I am a proponent of physically unplugging the temperature sensor from the RJ11 port on the charger. I do not like to have unattended batteries having the voltage compensated UP while they are sitting there doing nothing all winter. They only need enough voltage to maintain 100% SOC and a standard float voltage will do this. It is important, if you want to do this, to physically unplug the sensor from the charger itself not just remove it from the battery terminal. Removing the sensor from the battery, but leaving it plugged into the charger, will still result in voltage being compensated UP, all winter.
In cold climates where you are physically using the batteries regularly compensating UP is good. For storage, I am not a big fan of it. In my opinion the best option for cold weather storage is to fully charge the batteries and then physically disconnect them from the vessel, chargers and from one another. This is the safest storage option. Unattended chronic float charging is just an “oops” waiting to happen.
Battery Temperature Sensor Location
In this picture you can see the location of the battery temperature sensor.
It is important to mount the sensor directly to the battery post or battery case so it senses the temperature of the bank correctly. A temperature sensor should be mounted to the battery which has the most potential to get warmer than the others. For example, if your battery compartment backs up next to an engine room bulkhead the battery closest to that bulkhead would get the temp sensor.
Any terminal mounted temperature sensor also needs to be connected directly to a negative terminal, and not the positive terminal. The temperature sensor has the ability to fry the charger if connected to the + terminal and also the potential to be accidentally shorted. A battery temperature sensor can not be fused and still sense temp correctly. If following the applicable safety standards, such as the ABYC standards, a temperature sensor can not be connected directly to a + post.
Always keep in mind, when stacking terminals on a battery post, that the highest current potential terminal is always placed on the bottom. In this case the two 2/0 negative cables go below the temp sensor ring terminal. There is also a limit of four terminals per battery post. Use buss bars if you need more than four items on a battery post.
ABYC standards now also prohibit wing nuts on battery terminals if any wire connected to the battery is larger than 6GA AWG. Use standard nuts with locking washers or nyloc nuts if you have enough thread left for the nylon in the nyloc nut to thread over.
Charger Feed Wiring
Close Up With Covers Removed
Parallel Batteries – Optimal Hook Up
Parallel Batteries – Less Optimal Wiring
Negative DC Wiring
Wire The Temp Sensor & AC Wiring
Wiring Up The DC Side
Test & Program Your Charger
Let’s Keep This Site Running!
Like what you saw or read? Would you like to see more articles like this? Is so feel free to donate, support the site and keep it growing. I am trying my hardest to keep this information FREE. If you liked it, learned from it or I saved you some money feel free to make a small donation, that’s all I ask.