Battery Charger Recommendations

[Timccarpenter]

I've found that my old Xantrex battery charger has failed. I'm replacing the charger that charges two 27 group, 88Ah deep cycle batteries. Is it correct that I need a charger that outputs 10-20% of the total Ah of both batteries? That would be almost 40amps. Is that right? My old charger was 10amp (maybe that is why it is failing?). Also, recommended affordable chargers?

[kmacdonald]

IOTA chargers.

[GILow]

Originally Posted by Timccarpenter

I've found that my old Xantrex battery charger has failed. I'm replacing the charger that charges two 27 group, 88Ah deep cycle batteries. Is it correct that I need a charger that outputs 10-20% of the total Ah of both batteries? That would be almost 40amps. Is that right? My old charger was 10amp (maybe that is why it is failing?). Also, recommended affordable chargers?

I had the same question/confusion a few years back. It appeared, from what people were writing at the time, that I’d need a massive charger for my 675AH Trojan battery bank. (6 x T105s).

I thought at first the big charger was to prevent the batteries sulphating up or something, but I came to the conclusion that the reasoning behind the bigger chargers was some kind of assumption that you would not have enough TIME to recharge the batteries if you had a smaller charger. There was a mindset that you’d need to replace all of the charge in the bank in some really short time.

For me, that was not an issue, being practically 100% solar, so I went ahead and bought a Victron 25 amp charger for the times I am at the dock and the solar isn’t coping. Six years later my Trojan T105s are still like new.

Happy to be corrected if there is some other issue, but otherwise I cannot recommend the Victron smart chargers enough. Coupled with one of their cheap and practical Smartsense battery sensors you have practically infinite control and smarts plus a great level of future-proofing as well. Should you change to Lithium or something else down the track it’s just a few seconds works to log into the charger and set the new parameters.

[Tin Tin]

It is more complicated than this but to simplify it down. You have 88*2 = 176AH. Assuming discharge to 50% that leaves 88AH to charge up. A 10A charger will take 88/10 = 8.8hrs and longer - say 10hrs to fully charge - so any stuff like fridge running through the day will push this out further - so may be 12 hrs.


Double the charger and so half the time, to a point. A 40A charger might do 88A to say 90% within 2-3 hrs (20A to each battery = 27% of AH capacity). AGM will only accept charge within certian limitations so a 88A charger will not do it in 1 hr. (A LifepO4 battery is a different matter)


There are plenty of 40 A chargers on the market, get one that is suitable for marine use (so protected circuit boards from salt/moisture etc), tinned wires and so on. A cheap autmotive one will work, question is how long.

[more]

Originally Posted by Timccarpenter

My old charger was 10amp (maybe that is why it is failing?). Also, recommended affordable chargers?

no your charger not fail becouse you make some matematic.
hi charge 10A if on other side 50ah baterry or 500000000 ah batery.
he fail becouse some component inside eletronic die,maybe fuse,maybe rust in microprocesor legs,maybe condenser valid 0,1 $
who know what you can do. becouse this is 10A xantrex put in recycling box and buy
victron ip22 15/30A charger for 120$ perfect charger.if need more A for charger buy 2-3-4 pices

[more]

Originally Posted by kmacdonald

IOTA chargers.

this and similar chargers is maybe good for charging battery from 2000 meter from sea or other water. and humidity under 60%.
victron ip22 is best in world design charger so good and efficiency he don't have fan for cooling. best charger for peopel who time to time go in marina or run generator some time.or for peopel who always in marina with lead flood batery
not recommended for peopel with always conectet in marina with charger on with agm,lithium ,gel battery.
to agresiv charging 14,4V for setup 13,48-14V is user defined and every time you disconnect charger from shore you have small chance he dont remeber setup and automatic return for lead setup.
i never see this combo but this peopel yes.
https://community.victronenergy.com/...iguration.html

[GordMay]

You’re correct, the general rule of thumb is that battery chargers should be no more than 10% ➛ 20% of the Ah rating of the battery.

The general rule of thumb, for sizing a lead acid battery charger, is a maximum of C/5 [20%], or Capacity [in amp-hours] divided by 5.
So, a 30 -➛ 40 amp charger is probably the right size for a 176 Ah battery bank
[(2 x 88] ÷ 5 = 35.2].
Add additional charger capacity, when fixed DC loads [L] are present.

When the time allowed for charging is factored in [per GILow#3, & Tin Tin #4], the following formula is often used:
[(AH x K)/T] + L = I
where:
AH is the ampere-hour capacity of the battery
K is the battery recharge inefficiency constant (1.15 for lead-acid)
T is the desired recharge time [often 24 hours, from fully discharged*]
L is the number of amperes consumed by the fixed load
I is the ampere rating of the battery charger


* NFPA 110, the Standard for Emergency and Standby Power Systems, paragraph 5.6.4.7 (2) states that:
“The charger shall be capable of returning the fully discharged battery to 100 percent of its ampere-hour rating, within the time specified* in Table 5.6.4.2" (24 hours (NFPA Level 1 installations).

[GILow]

Yeah, everyone is marching down the formulas route, and the “how many hours to charge from 50%” thing.

But I reckon neither are important. If the battery is down to 50% when you get to the dock (very unlikely), then who really cares how many hours it will take to recharge if, like most boats, it will remain at the dock for days or even weeks.

My battery bank has lived almost exclusively on solar, with a 25 amp backup for the time at dock, and it’s perfectly fine. A big shore charger is not a necessity, it’s a mild convenience at most, a waste of money in all likelihood.

[GordMay]

Originally Posted by GILow

Yeah, everyone is marching down the formulas route, and the “how many hours to charge from 50%” thing.

But I reckon neither are important. If the battery is down to 50% when you get to the dock (very unlikely), then who really cares how many hours it will take to recharge if, like most boats, it will remain at the dock for days or even weeks.

My battery bank has lived almost exclusively on solar, with a 25 amp backup for the time at dock, and it’s perfectly fine. A big shore charger is not a necessity, it’s a mild convenience at most, a waste of money in all likelihood.

Indeed.
As I said: "... the general rule of thumb is that battery chargers should be no more than 10% ➛ 20% of the Ah rating of the battery.."

[GILow]

Originally Posted by GordMay

Indeed.
As I said: "... the general rule of thumb is that battery chargers should be no more than 10% ➛ 20% of the Ah rating of the battery.."

Yes, I understood that. But for newbies it's very confusing and almost needs to be highlighted in the way that you have here.

[derfy]

Know that the "battery charger" like a Xantrex performs three distinct functions...1) charging the house battery from shore (or your generator) AC power, 2) providing AC power to the boat's AC Panel from the battery (the inverter function), and 3) switching AC power to the AC Panel between the battery (invertor) and the shore (or generator) power.

You will want to know the specifications for all these functions when your replace your Xantrex.

Your house battery might be charged from 1) the Xantrex, and/or 2) your engine alternator, and 3) your solar panel/wind generator charge controller

The amount of current delivered to your house battery during charging is controlled by the Xantrex when your plugged into shore power or running your generator. When you are motoring, the charge current is controlled by the alternator's voltage regulator. When you are at anchor or sailing, the charge rate is controlled by the solar panel charge controller. Each charge source needs to be configured for your battery.

Your house batteries have a specified charge rate profile that depends on the battery chemistry/structure, state of charge, and the temperature. Generally they follow three phases of charge: bulk, absorption, and float. You will need to learn about this for your batteries and program your chargers (all of them) to follow the recommended profiles. Most chargers have pre-programmed profiles, and can be tweaked.

You may want to consider, when choosing your Xantrex replacement 1) the requirements to charge your batteries, 2) the requirements for AC power on your boat fed by the Xantrex and battery, 3) AC power fed thru the Xantrex from shore or the generator, 4) the amount of standby power consumed by the inverter (drain on your battery in addition to the house AC loads), 4) the possibility to upgrade Lithium Iron Phosphate batteries in the future. Profiles and voltages are different for lithium.

I replaced my old iron core Xantrex with a new solid state Xantrex XC Pro Marine 2000. It's ok, it works, the controls are a little flakey (I push the on/off button several times to get it to work) and I have had to reset it a couple of times. It survived a direct lightning hit to my mast that killed all other electrical devices. I wish I had gotten a 3000.

Know that wiring 12v chargers is very tricky. You are dealing with very high current and must have clean, properly sized connections: wire, swages, terminals, etc, accurately torqued, using conductive grease such as NO OX ID. Don't handle surfaces with your bare fingers. Else you will get voltage drop, power dissipation in the contacts, corrosion, and risk of fire. My boat has ~100 Amps of current flowing through these connections during peak charging. Just 1 Milli-ohm of resistance will cause a 0.1 volt drop across one connection. Several of these in series and you have lost a half a volt between the charger and battery - way too much. You are also dumping 10 watts into each 1 Milli-ohm terminal interface. (Power = I^2 * R) It will be warm to the touch.

Good luck and do it right. Welcome to the world of boat ownership and electrical engineering 101.

[Exile]

Originally Posted by GordMay

Indeed.
As I said: "... the general rule of thumb is that battery chargers should be no more than 10% ➛ 20% of the Ah rating of the battery.."

Originally Posted by GILow

Yes, I understood that. But for newbies it's very confusing and almost needs to be highlighted in the way that you have here.

Agreed! It's a max not a min, and something not well understood in my experience. Except for LithPO4 that is, which can apparently take as many amps as can be provided (within reason).

Interestingly (to me anyway), is that my now 14 year-old Xantrex 50-amp charger only (no inverter combo) will charge each of my 3 (8D) batts one at a time based on sensing their respective states of charge. Each battery is rated at 255ah so that's right about at the 20% mark (when new). The new Xantrex chargers (TrueCharge2) don't have this feature, and I have thus far been unable to find any (marine-specific standalone chargers) that do. The closest I've found are 60-amp chargers that would charge all 3 at the same time. So that's 765ah being charged by a max of 60 amps or at only about 8%. Of course, some mfgs (e.g. Xantrex, Sterling) allow you to combine two of their chargers together which is probably what I would wind up doing.

Again, I'm talking about standalone marine chargers here and not combo charger/inverters. The latter seem to be available with higher amp chargers. Anyone come across anything different?

[twofingerpoi]

My original Sentry charger fried my two 4D house (2 x 190Ah) and Group 27 start lead acid, so I upgraded to AGM start and LiFePo4 house (280Ah) with Victron IP43 and BMV712 shunt with Orion XS which I can manage from the Connect app on my iPhone.

https://www.victronenergy.com/charge...t-ip43-charger
https://www.victronenergy.com/upload...charger-EN.pdf
https://www.victronenergy.com/displa.../bmv-712-smart
https://www.victronenergy.com/panel-...victronconnect

[CarinaPDX]

Consider the possibility that in the not-so-distant future you might want to convert to LiFePo4 batteries. It makes sense to buy a charger now that is designed to charge them safely, as well as the current lead acid batteries. Unfortunately lithium chargers are pretty thin on the ground: AFAIK Victron is the only one, but others claim to have a lithium setting - which is almost never actually appropriate. You will need a charger with a remote on/off, a programmable absorption voltage, absorption time, and crucially a current charge cut-off setting. Voltage alone is not enough - it is quite possible to overcharge (in the sense that it is being held too high for too long for the health of the battery) a LiFePo4 battery at a fairly low voltage; when the battery stops accepting charge (i..e. low current) then the charger needs to switch to "float" (not really a float but let that pass for now), regardless of voltage.

Greg