3 x 105ah domestic, 1 x 95ah Engine. Sealed Lead acid. Do I really need 10-20% of battery capacity or is a 20a Victron charger enough ?

[aidancoughlan]

A question of charging, do I really need the "recommended" 10% of battery capacity ? Is a new 20ah charger enough to replace the old 20a charger for a 315ah domestic battery bank overnight , assuming not discharged below 50% ?

• The batteries in both banks (Numax XDC31MF domestic 105ah x 3 , VARTA 95ah starter ) are approximately 5 years old - installed when I bought the boat & appear to be in good condition - no problems.
• Both banks are "sealed" lead acid batteries
• They have been on regular shorepower charging most of their life via a Truecharge 20ah inherited with the boat (1990's Vintage, before Xantrex appear to have taken them over).
• There is also a Hitachi 80amp alternator (without smart regulator on the engine)
• The boat has just moved to a mooring this year (3 hours away), and there is no solar or wind charging capability on board
• I have had & anticipate relatively frequent marina overnights during the summer (at least once every 3-5 weeks or so for weekend visits, without any significant battery loads in between). I charge the batteries on shorepower on those occasions - and anticipate access to shorepower over the winter.
• So far, this doesn't seem to have caused any problems in the few weeks in between shore-power charging , the batteries seem to hold charge in between just fine.

Although we are mostly weekend sailors - we have just spent several weeks on board on our annual cruise, and discovered on day#1 that the Truecharge 20a has finally given up the ghost. That said, the batteries seem to have survived OK under load for two weeks without shorepower charging.)

• During the cruise we moved around and had daily engine runs most days (average 3-5 hours engine use per day).
• Our usage is approximately 2-6ah under sail depending on whether we have plotters, AIS , radar etc. switched on.
• We run the fridge (4/5amps) while the engine is running, and perhaps for a few hours in the evening.
• Our usage at night is frugal - cabin lights, phone charging etc - especially when at anchor or on moorings.
• We never saw the battery voltage go under 12.4 volts (circa 60% charged?) at any stage (usually checked late in the evening maybe 4-5 hours after last running the engine)
• On our last day, after resting overnight (10-12 hours) the house/engine banks were at 12.8V and 12.9V respectively (circa 90% charged?). It remains to be seen if they drop between last weekend and this coming weekend after resting further.

However, I want to replace the old 20A Truecharge relatively quickly (ie. this weekend if I can) to keep the the batteries topped up from now until end of season, and over winter. This raises some questions about the replacement charger

• Do I really need a minimum of 10% , which would indicate a 30a charger (or 40a if counting engine battery also) ? A 20ah charger would be simplest (re-use existing wiring, the "input" cabling route is unknown at present)
• Is a 20ah charger enough to charge a 315ah domestic battery bank overnight , assuming not discharged below 50% ? 20ah x 8 hours would be 160ah or 240ah over 12 hours - is that the way to gauge it ?

My current thinking is

• Go for a 20a Victron IP22 Blue smart charger in the short term : we seem to have survived on the Truecharge 20a after all, and this will minimise wiring issues. https://jtmpower.ie/products/victron-blue-smart-ip22-charger?variant=40738545893572
• Follow this (over winter) with a solar panel of some sort (for use next season to keep the batteries topped up between visits to the mooring) - maybe something like this Victron https://jtmpower.ie/products/solar-charger-for-campervan-or-van-batteries-package
• Follow this with a second Victron IP22 charger next season / over winter if we add the planned Electric Windlass (I understand two 20a Victron chargers can be "networked" to act as a larger 40a charger).
• To improve charging capability while at anchor / cruising away from marinas - consider adding an alternator smart regulator (Adverc, Sterling ? ... is there an equivalent Victron product /advantage to to keeping all the kit the same?).

I'm sure there's a flaw here somewhere , what might the flaws be , or does this seem reasonable given our usage & recent experience?

 

[Tranona]

The way you describe your usage pattern a 20A charger OK, but if you are buying new then suggest you go for a 30A. On my last boat I had 285Ah bank and a 40A charger, but even with a 50% discharged bank never needed more than 20A. Remember if you are starting at 50% you are limited by the declining acceptance rate as the batteries get near to full. No need to worry about the start battery or the windlass as while they draw high current it is for very short periods and few amps then the alternator fully charges them in minutes. In the boat I am refurbing I have a 190Ah AGM house bank, 32Ah start AGM and 105Ah bow battery for windlass and bow thruster. Apart from engine alternator charging is 15A mains to house bank, trickle charger to engine start and B2B (30A) from start to bow.

For your situation on a swinging mooring a solar panel is good to keep the house bank topped up. The engine start should not need anything, but a means for connecting the house bank to the starter for emergency would be good. For cruising no need to do anything to increase engine charging as the batteries will not accept more than they can take - and that will be less than what the alternator can output. Solar is the way to go if you want to spend more time off grid.

Your batteries are probably coming near replacement (5-7 years for leisure batteries). For replacements consider AGMs which have fallen in price substantially as they are now commonly used in cars. Higher charge acceptance, lower self discharge and typically twice the life (measured by discharge cycles) for somewhere around 30% price premium. My 2*95Ah AGMs cost £230. similar capacity leisure are around £95 each. You probably don't need a 95Ah engine start. For engines up to 30tp a 65 Ah is more than enough. I chose a high output Odyssey as used in racing cars for space reasons. Expensive but past experience with Red Flash equivalents is good - the one in my Morgan is the original from when I bought it new in 2003!.

 

[Momac]

I have 2 x120Ah domestic, 110Ah starter and 65Ah bow thruster.
The Victron bluesmart 30A with 3 outputs which I fitted a year ago copes with this with no apparent issues.

Unless you require more than 30A while connected to shore power (I certainly do not) or unless you want to charge your batteries faster there isn't really a need to go any bigger .

 

[aidancoughlan]

Thanks you very much folks. You are both suggesting 30a (although Tranona reckons 20a will do if need be based on my current usage).

At the moment I am still inclined to go with 20a, just for ease of replacement (ie. I don't have to replace wiring with a higher gauge). I read that with the Victron chargers, you can add another and run them in parallel (they are designed to do this) to increase the output. I will plan to do this at a later stage to give 40a (or maybe up to 60a, the cost different seems to decrease the higher you go) if I find 20a limiting, or my needs/usage increases.

If my batteries start to die soon as Tranona predicts (5 yrs+), I may look at AGM's which will require new higher output fast charging to make the most of them - and associated cabling. Maybe I will review it then.

 

[Tranona]

Thanks you very much folks. You are both suggesting 30a (although Tranona reckons 20a will do if need be based on my current usage).

At the moment I am still inclined to go with 20a, just for ease of replacement (ie. I don't have to replace wiring with a higher gauge). I read that with the Victron chargers, you can add another and run them in parallel (they are designed to do this) to increase the output. I will plan to do this at a later stage to give 40a (or maybe up to 60a, the cost different seems to decrease the higher you go) if I find 20a limiting, or my needs/usage increases.

If my batteries start to die soon as Tranona predicts (5 yrs+), I may look at AGM's which will require new higher output fast charging to make the most of them - and associated cabling. Maybe I will review it then.

Not sure why you think you will need new cables to go to a 30A charger, nor change your charging to go to AGMs. charger profile is essentially the same and your existing alternator will charge the AGM OK. That is one of the benefits that come with AGMs - big step up in performance and life without major changes to existing charging.

 

[PaulRainbow]

Little difference in cost between a 20a and 30a, more than 30a would be unnecessary. No need to fit bigger cables (unless they are undersized now. A Victron Bluesmart 30a will be the best option.

 

[Momac]

If my batteries start to die soon as Tranona predicts (5 yrs+), I may look at AGM's which will require new higher output fast charging to make the most of them - and associated cabling. Maybe I will review it then.

The Victron Bluesmart has a AGM setting
You would need separate chargers unless you change every battery to AGM

 

[PaulRainbow]

The Victron Bluesmart has a AGM setting
You would need separate chargers unless you change every battery to AGM

You can use the same charger for a mix of AGM and SLA batteries, the charging voltages are fairly close.

 

[aidancoughlan]

Not sure why you think you will need new cables to go to a 30A charger, nor change your charging to go to AGMs. charger profile is essentially the same and your existing alternator will charge the AGM OK.

Yep, understand the bit about AGM's not needing a different charger - I just noted that AGMS (If I change to them) will accept charge faster , and could perhaps benefit from a larger charger during a few hours at the dock.

Little difference in cost between a 20a and 30a

Yes, I noticed that - even higher the incremental cost is relatively small. Cost wasn't my reason for avoiding higher than 20a.

Not sure why you think you will need new cables to go to a 30A charger,

No need to fit bigger cables (unless they are undersized now.

Hmm, OK. Maybe I've jumped the gun on that one. I don't have the detail of the original cable sizing, but I assumed they (may) have been sized for the original 20a charger. I thought it dangerous to upgrade to a larger charger without upgrading the "input" cable - which goes an unknown route thorough the boat I think behind headlining, bunks etc. As I mentioned, my main reason for sticking with a 20a was to avoid any re-cabling hassle in the short term. I might wait till I visit the boat this coming weekend and attempt to determine the AWG/size of the current cables & run length to see if they were originally sized to cope with a larger charger than the original. Am I missing something - I am assuming that a larger charger will require larger cables (unless the original cables were over-specc'ed or specc'ed generously). I am happy to pay the marginal cost for a bigger charger - as big as will operate safely on the existing cables. I just don' t want the hassle (in the short term mid-season) of re-wiring.

You would need separate chargers unless you change every battery to AGM

You can use the same charger for a mix of AGM and SLA batteries, the charging voltages are fairly close.

Yep, aware of the potential mis-match - potentially a benefit of two smaller chargers (one configured for AGM, the other for lead acid etc.), but I am likely to stick with the one type of battery on both banks for simplicity. interesting what PaulRainbow says though, it may be fine with a mix of SLA (engine) and AGM (new domestics) if I change them.

I guess the key question right now is for me to answer - is my cabling sufficient for an upgrade to a 30a charger or higher. I can't understand how you can be sure I won't need to change cabling.
Maybe I will hold off for another week before purchasing a charger (and hope the batteries will be OK in the meantime) - and go for the bigger one if I think the cabling will cover it.

 

[PaulRainbow]

Yep, understand the bit about AGM's not needing a different charger - I just noted that AGMS (If I change to them) will accept charge faster , and could perhaps benefit from a larger charger during a few hours at the dock.

You do not need a separate charger just becasue one system is SLA and one is AGM, millions of boats are built with this setup, it's common to have AGM bow thruster batteries and SLA domestics, for example.

Hmm, OK. Maybe I've jumped the gun on that one. I don't have the detail of the original cable sizing, but I assumed they (may) have been sized for the original 20a charger. I thought it dangerous to upgrade to a larger charger without upgrading the "input" cable - which goes an unknown route thorough the boat I think behind headlining, bunks etc. As I mentioned, my main reason for sticking with a 20a was to avoid any re-cabling hassle in the short term. I might wait till I visit the boat this coming weekend and attempt to determine the AWG/size of the current cables & run length to see if they were originally sized to cope with a larger charger than the original. Am I missing something - I am assuming that a larger charger will require larger cables (unless the original cables were over-specc'ed or specc'ed generously). I am happy to pay the marginal cost for a bigger charger - as big as will operate safely on the existing cables. I just don' t want the hassle (in the short term mid-season) of re-wiring.

The "input" cable will be 240v shore power, no need to touch that. Cabling from the charger to the batteries is almost certainlu OK, but if it isn't, you just get a small voltage drop, nothing dangerous will happen in this case. Boat cables are generally not precisely matched to the loads they are expected to carry, it would be ridiculous to even attempt such a thing. Cable sizes tend to be 1.5mm, 2.5mm, 4mm, 6mm, 8mm, 10mm, 16mm, 25mm, 35mm etc.

If you fit the 30a charger and find the voltage drop is more than ideal you can still use the charger and uprate the cable at the end of the season.

How far is the charger from the batteries ?

 

[superheat6k]

Little difference in cost between a 20a and 30a, more than 30a would be unnecessary. No need to fit bigger cables (unless they are undersized now. A Victron Bluesmart 30a will be the best option.

Since I fixed my Bluesmart 30a just over a week ago my electricity consumption has reduced from ~ £3.50 per week to just £0.30. So for the £200 I paid, payback will be achieved in ~14 months. That excludes the fact my batteries will now likely last twice as long from the gentle treatment they will now receive.

This weekend with lights on during the evening I did not observe the amps draw rise above 6a on the usage record as recorded on the blue tooth interface. I was on shore power and the fridge has a 240v / 12v option so I switched this to 240v setting.

 

[aidancoughlan]

The "input" cable will be 240v shore power, no need to touch that.

Ah, OK !!! - I think this is what I was missing. I assumed (without thinking it through) I would need to upgrade the AC cabling in the boat to the charger (the "input cable"). My rationale was that if I doubled the charger AMP rating (eg. from 20a to 40a) , I would need to double the size of that cable. I realise now though that at 12volts, the 30 amp charger will consume 360 Watts at full tilt. However, 360 Watts on 240-volt will be only 1.5 Amps?. A standard 16AMP shore-power lead in UK/Ireland seems to be 1.5mm2 or 2.5mm2 so I guess there is plenty of spare capacity already on that side. I will check, but feel certain the AC cable into the existing battery charger was easily 1.5mm2 if not 2.5mm2.

Cabling from the charger to the batteries is almost certainly OK, but if it isn't, you just get a small voltage drop, nothing dangerous will happen in this case. Boat cables are generally not precisely matched to the loads they are expected to carry, it would be ridiculous to even attempt such a thing. Cable sizes tend to be 1.5mm, 2.5mm, 4mm, 6mm, 8mm, 10mm, 16mm, 25mm, 35mm etc. If you fit the 30a charger and find the voltage drop is more than ideal you can still use the charger and uprate the cable at the end of the season. How far is the charger from the batteries ?

There were two + outputs and a negative from the Xantrex 20a charger. My hunch /recollection from looking it is that it was 1.5mm2 wire (ie. the regular lighter shore power cable) from charger to batteries.
The distance is approx 1.5 metres (one way) from charger to battery . ..

• This gives a voltage drop of about 6.35% (= 0.762 volts drop) at 20 amps.
• If I upped it to a Victron Bluesmart 30a charger, and used the same cables - it suggests a voltage drop of around 9.5% (=1.14 volts) at 30 amps.

These figures from 12voltplanet calculator here.

I think my concern here might just be another mis-understanding on my part. I was assuming it would be like a load on the cable from a battery to a device it is powering - enough current flowing to satisfy the load, and running into trouble (resistance/heat) if the cable is under-sized. I was thinking of the battery as the "load" (with potentially sizable power demand depending on how discharged it was) , and the battery charger as the source of the power. I assumed a larger charger would automatically mean a larger amount of current flowing through the cable. I get the feeling now (from PaulRainbow's post above) that this is not necessarily the case and that the battery charger current output will be limited by both the battery (based on what the battery will accept), and the cable - such that under-sizing the cable (if that happened) would not be a risk factor, just an introduction of an inefficiency in the charging system. Is that the case?.

Apologies if I have finally cottoned on, and it has taken some time for the penny to drop !. I will definitely go for the 30a charger if the understanding above is correct and it doesn't represent a new risk in the existing (1.5mm2) cabling to the batteries - and I will consider upsizing it later for efficiency reasons if needed. For now, I just want to renew my means for charging the batteries overnight whenever I get to shore-power, the efficiency is secondary.

Apologies also if I have got it totally wrong and am barking up the wrong tree !!

 

[PaulRainbow]

Ah, OK !!! - I think this is what I was missing. I assumed (without thinking it through) I would need to upgrade the AC cabling in the boat to the charger (the "input cable"). My rationale was that if I doubled the charger AMP rating (eg. from 20a to 40a) , I would need to double the size of that cable. I realise now though that at 12volts, the 30 amp charger will consume 360 Watts at full tilt. However, 360 Watts on 240-volt will be only 1.5 Amps?. A standard 16AMP shore-power lead in UK/Ireland seems to be 1.5mm2 or 2.5mm2 so I guess there is plenty of spare capacity already on that side. I will check, but feel certain the AC cable into the existing battery charger was easily 1.5mm2 if not 2.5mm2.


There were two + outputs and a negative from the Xantrex 20a charger. My hunch /recollection from looking it is that it was 1.5mm2 wire (ie. the regular lighter shore power cable) from charger to batteries.
The distance is approx 1.5 metres (one way) from charger to battery . ..

• This gives a voltage drop of about 6.35% (= 0.762 volts drop) at 20 amps.
• If I upped it to a Victron Bluesmart 30a charger, and used the same cables - it suggests a voltage drop of around 9.5% (=1.14 volts) at 30 amps.

These figures from 12voltplanet calculator here.

I think my concern here might just be another mis-understanding on my part. I was assuming it would be like a load on the cable from a battery to a device it is powering - enough current flowing to satisfy the load, and running into trouble (resistance/heat) if the cable is under-sized. I was thinking of the battery as the "load" (with potentially sizable power demand depending on how discharged it was) , and the battery charger as the source of the power. I assumed a larger charger would automatically mean a larger amount of current flowing through the cable. I get the feeling now (from PaulRainbow's post above) that this is not necessarily the case and that the battery charger current output will be limited by both the battery (based on what the battery will accept), and the cable - such that under-sizing the cable (if that happened) would not be a risk factor, just an introduction of an inefficiency in the charging system. Is that the case?.

That is correct. If it's 1.5mm cable it is undersized, i would replace with 6mm cable as soon as convenient.

 

[aidancoughlan]

Thank you so much @PaulRainbow - I've noticed your input on other similar batteries & wiring threads in the past , and I'm grateful to you for patiently sharing your expertise here.

• I do understand the very basics of DC wiring, but my use of it is infrequent enough that I don't recognise cable sizing fluently by sight, and every foray into this is slow & researched before I do anything. I think I was probably incorrect and mis-led you above when I suggested the cables to the batteries were 1.5mm2. From recollection (I am just working from memory until I get back to the boat), the rough size (in diameter) of the cable/insulation was roughly like a lighter shore power lead (ie. like a 1.5mm2 shore power lead), but of course the shore power lead has three cores, these have only one - so they are probably much larger than what I suggested. I will check when I am back on the boat.
• I have always kept away from AC (hence my confusion about the AC power lead earlier).

Thanks for clarifying the mis-conception about the risk in the charging cable to the battery versus inefficiency - I wouldn't have had a clue about that !.

 

[pcatterall]

With your usage pattern my first action would be simple small solar panel.

 

[aidancoughlan]

Just to close this out... I picked up a Victron 30a bluesmart charger in anticipation of it being a direct replacement.
When I got back to the boat....

• The batteries were at 12.6v (after resting for the week) so we hadn't depleted them too much after our fortnight aboard with just engine charging.
• The cables from charger to batteries on the old Truecharge 20a were indeed beefy enough 6mm (not 1.5mm2 as I had guessed badly from memory)... any bigger and the charger ports may have struggled to accept them.

I replaced the original (using the same cables), gave the batteries a good charging over the weekend before going back on the mooring. No problems, and the Victron seems a nice little unit. The original charger was wired directly to AC, so I put a socket box (with USB ports) there instead and plugged the new charger (which comes with a UK plug) into that.

I will plan on installing solar panel & regulator over the winter as I am likely to stay on mooring next year.

Many thanks for the help & advice received here on the forum.

 

[PaulRainbow]

Just to close this out... I picked up a Victron 30a bluesmart charger in anticipation of it being a direct replacement.
When I got back to the boat....

• The batteries were at 12.6v (after resting for the week) so we hadn't depleted them too much after our fortnight aboard with just engine charging.
• The cables from charger to batteries on the old Truecharge 20a were indeed beefy enough 6mm (not 1.5mm2 as I had guessed badly from memory)... any bigger and the charger ports may have struggled to accept them.

I replaced the original (using the same cables), gave the batteries a good charging over the weekend before going back on the mooring. No problems, and the Victron seems a nice little unit. The original charger was wired directly to AC, so I put a socket box (with USB ports) there instead and plugged the new charger (which comes with a UK plug) into that.

I will plan on installing solar panel & regulator over the winter as I am likely to stay on mooring next year.

Many thanks for the help & advice received here on the forum.

Thanks for the update Aidan

 

[superheat6k]

So whereas the Victron has resolved the excess power draw, I think the old charger has cooked the Port battery, as despite having decent terminal voltage, as soo as any load is applied the voltage drops to just a few volts.

Quite an interesting fault finding process ...

Following a bumpy passage down the western Solent yesterday, arrived at Yarmouth - Port engine would not shut down. I stopped it myself my manually lifting the solenoid lever.

But neither would the engine re-start.

Then found a partially loose negative connection at the port battery.

Then still no power, so cleaned all the battery connections to the port battery. This didn't work either, except the stop solenoid now works, just no start.

Opened the panel to the electrics behind the helm station to discover two DC trips - one of which was down, so reset and all systems restored.

So then this morning I had to move berth in Yarmouth and after a session using both stern and bow thruster yet again no engine stop control. OK the thing had tripped again. Neither was the stern thruster working beyond a clicking noise.

So I then reset the trip and the thruster was restored - but the stern thruster draws its power from the port battery and does not need to pul power through the trip, however only with the batteries in 'All' would it work - so its pulling power through from the Stbd bank.

So time to look more closely and the Port battery is goosed. Puts out 14.0 v with no load, when in fact the Victron is providing the power.


The batteries are three Varta LFD230 12v 230AH 1150 CCA. These are arranged two in permanent parallel forming the Stbd and d
Domestic bank. The third is a lone battery on the Port bank, so is isolated for engine start only when not on shorepower.

So I have the following question ...

The Port is only connected in parallel with the stbd bank when the engines are running, and both banks have separate charger feeds from the Victron charger. Can I use any similar 220 - 240 AH for the Port, as this is only being used for Port engine start and the stern thruster ?

Thanks.