Battery charging from shore power

[Jerry]

It turns out I got lucky and will be on a dock my first year with the boat. This leaves me with available shore power and wanting to put a charging system in to keep the batteries topped off from the available shore power.

Can I get a couple suggestions what to use for this and how to wire it?

My boat came through with 2 - 35 Amp AGM batteries and has a BEP Marine 714-100A-DS dual sensing VSR that PCI is starting to supply with the boat. Switch supposedly charges the battery it is not set to (2 if set to 1) when 1 is full (13.7 V).

I would think because of time at the dock I do not need a very large charger but I do want something that will not hurt the batteries when left connected.

Thanks for any help.

[Dan]

If you're planning on doing any longer trips, you'll definitely want a larger house bank. As for shore-power based chargers, I have been recommending the Iota chargers, as they're very well made, and quite reasonably priced. You can get them at: http://store.solar-electric.com/bach1.html

AGM batteries have a higher current acceptance rate than wet-cell batteries, so the 30-amp charger or so would probably be okay, and would give you decent recharging capabilities when you upgrade to a larger house bank. BTW, don't mix AGM and wetcell batteries when you go to buy your new house bank.

Another option would be to get a small solar panel. I've written about solar power on boats on my blog.

[Ron]

Jerry -

Regardless of the size of the charger (and too big is probably not a good idea), you've got to make sure that it's "multistage" (3 stages) where the final stage will "float" it. Note that this does not mean "trickle". I use a 1.25 amp "Delran Battery Tender" to take care of my 2 (standard size) AGM's. Similar setup as yours - it's normally plugged in when at my dock or on the lift.

I've been using these Battery Tenders for many years - probably have 10 of them now. I use them to keep car batteries topped off. Other hobby is restoring 50's and 60's sports and muscle cars. Some of these batteries must be over 10 years old now and they stlll start up instantaneoulsy - even if the car is started only once or twice a year.

[Jerry]

Ron,

How do you have it wired? I am wondering if I should just wire in parallel with the Outboard alternator since I have the sensing VCR in the circuit. I am just not familiar with DC wiring.

Dan,
30 Amp charger seems a bit of overkill for any size batteries when the charger is going to be plugged in overnight while in a slip. Can you give me a little more of your reasoning? I have read your solar wright up an may do that next year.

Thanks,
Jerry

[dcsailing1]

Here is what we did: A “smart” 20 amp three stage AC battery charger handles, senses and charges, up to 3 separate batteries. It will “float” charge any full battery. Since we added some high amp consuming loads, radar and an electric anchor windless, we made some other modifications to the stock 12volt layout. If there is any interest in these mods I will be glad to share.

[Dan]

Jerry—

You've got to remember how batteries charge. All rechargeable lead-acid batteries, whether they're AGM, Wet Cell or Gel, will charge fairly quickly to about the 85% of charge capacity... once they hit 85%, the current acceptance rate drops very dramatically, going from bulk charging to absorption charging... once the batteries are fully charged, the intelligent chargers will go in to float mode.

Batteries tend to have problems if not charged fully on a regular basis or if overcharged constantly. If the batteries are left in a state of discharge for an extended period of time—the lead plates that make up the internal structure of the batteries start to sulfate...where the lead is converted to lead sulphate crystals, which generally do not convert back to lead. This reduces the batteries actual capacity. Do this often enough, the batteries die. If the batteries are overcharged, they can boil off electrolyte. In the case of wet cells, this means that they need to be monitored more often and have water added more often—in the case of AGM or Gel batteries, the electrolyte can be boiled dry, killing them.

When you're out cruising on a Telstar, if you are relying on a shore-power charger to keep your batteries topped off, you need to have a fairly decent sized charger, since you may be using the batteries fairly heavily while anchored out. Then when you get back to a marina slip, say for a single night's stay, you have to have the ability to put back most, if not all, of what was used while anchored out. The outboard motor has a very, very limited charging capacity, and if you've got your boat equipped with a refrigerator, navigation lights, cabin lights, stereo, etc... you'll be using more than the outboard can put back into the batteries, unless you're motoring constantly.

Also, as a general rule, lead-acid batteries last far longer if you do not discharge them too deeply. Ideally, you'd only discharge them to the 50% depth of discharge level. This ends up giving you the most battery power for the money spent as a general rule. If you discharge a battery deeply on a regular basis, say to 80% DOD, then you can reduce the number of charging cycles that the battery is capable of handling by a significant percentage.

Typically, you should calculate your battery bank size by doing an energy budget. I generally recommend you do one for when you're typically at anchor and one for your usage when underway, and then take the higher number of the two as the basis for your energy budget. You do this by taking the amperage a piece of equipment uses and multiplying by the number of hours you would typically be using it. Then you add up all the numbers to get the total number of amp-hours you use per day. I'd point out that the most accurate way to do this is to add a battery monitor, like the Victron BMV 600, which will keep track of your actual usage.


image courtesy of jamestown distributors.

Once you have a rough budget, you have to decide how many days you want to go between charging the batteries. That gives you a basis for sizing your battery bank. Say your daily amp-hour usage comes out to 50 amp-hours and you decide you want to be able to go two full days between battery recharging, since you will generally anchor out for a weekend... leaving Friday evening and getting back to the slip on Sunday evening. That means you need 100 amp-hours of battery capacity. However, since you only want to discharge your batteries to the 50% DOD level, that means you need 200 amp-hours of battery bank.

Now, Sunday evening comes around, and you're back at your slip. You plug the boat into the shorepower system. Wet cells can generally accept about 20-25% of their amp-hour capacity in amps during the bulk charging phase, AGMs can accept a lot more generally. I don't like gels, and won't discuss them, since I believe they've got the worst characteristics of the three types. You have to put back 100 amp-hours.

If you have a 1.25 amp trickle charger, it is going to take a really long time... over 80 hours, since lead-acid batteries self-discharge, with wet cells losing as much as .5% per day on a hot summer day. If you have a 30 amp charger, like the Iota 30 I mentioned... you'll go from 100 amp-hours (remember the batteries are at 50% and you have a 200 amp-hour bank) to 85% charged pretty quickly... say in about 2.5 hours (30 amps x 2.5 = 75 amp-hours). To get from the 85% DOD level (170 amp-hours) up to 100%, may take another eight hours.

Now, if you're cruising for a week, and stop in the marina every other night, you'll probably be fine with a 30 amp charger. With a 15 amp charger, your batteries will slowly drop lower and lower, and you'll end up killing them prematurely, since the first stay at a marina, they'd get up to say 90%, then the next two days would drop them to the 40% level... and the next marina stay would only bring them to 80%...then the next two days would drop them to 30%...etc, until you're stuck someplace with dead batteries.

IMHO, a good battery monitor is one of the wisest and best investments you can make on a boat, if you plan on doing anything more than just weekending on it.

Dan,
30 Amp charger seems a bit of overkill for any size batteries when the charger is going to be plugged in overnight while in a slip. Can you give me a little more of your reasoning? I have read your solar wright up an may do that next year.

Thanks,
Jerry

[wingman]

Ok, here is the alternative view.

Eliminate the refrigerator, the GPS (except a handheld that plugs into the output on the chart table), the stereo (except the boom box that you take when you REALLY must have the outside world intrude), The solar panels that block wind AND add weight, and any other electrical equipment that is not necessary to make the boat go fast in deep (enough) water. You will be surprised how long those two puny batteries last. Remember that pull starter is very reliable even if both batteries are totally dead!

Using actual paper (laminated book type) charts is a lot more interesting than looking at a PC while sailing and was the way sailors sailed for thousands of years before GPS. Heck, I look at PC all day at work, I want nothing to remind me of that while sailing. I will admit that I use the handheld GPS for distance racing and for tuning, but not for fun.

As for recharging the batteries at the dock, we use a portable charger when necessary, which is very rarely if you sail at least once a week and thus run the engine enough to replenish the juice required for the instruments. This means less weight on the boat which equates to faster sailing!

The Telstar is a simple and cheap boat to sail, but, like any boat, the more stuff you put on it, the more time you spend working on the boat and the less you spend sailing. Also, the slower you go. If you want to go slow and have lots of toys, buy a used 40' monohull for $30K! It will not even notice all the extra weight. Especially while you sit at the dock in 90 degree heat and sweat out wire runs.

John

[Ron]

I've sailed (no motor) for 10 to 12 hours with the fridge set to "cool", stereo blasting with Jimmy Buffet on all 4 speakers, all instruments and the chartplotter on, autopilot and remote on, vhf on, etc. Never had a problem restarting with the two small agm's. Would they last till the next day if I anchored at that point? Probably not, but I'd be almost home again at that point. The amount of capacity that you need depends on what you expect to use. A 2 week trip into the boondocks is another story. My 1.25 amp Battery Tender, plugged into the AC socket and wired to the 2 way switch, is all I need.

[rbw]

I am about to install a 30 A shore power inlet, panel, circuit breaker on my Telstar 28. Can anybody tell me the best location for the inlet and the panel. At what location on the boat were these factory installed, for instance? Thanks for the info.

Cheers,
Rick Williams
"Trout Lily"

[Ron]

The shore power inlet is on the starboard side, and just forward of the first stanchion for the aft pulpit. The breakers are above the chart table. I'd take a picture for you, but the boat is now folded, mast down, strapped to my boat lift, and covered for the summer season. I'm using a 10 amp Guest battery charger to charge or float the 2 AGM's. Its got two 5 amps circuits.

I just checked and found an old photo showing the location of the Marinco 110v inlet.