2008 Hunter 36 here. Not interested in the expense and work of converting to lithium batteries. Currently have a single lead acid group 24 as starting battery, and house bank of 2 Group 31, also old school lead/acid. Considering adding more to the house bank. Currently located in port cockpit locker but no real room for more and the boat already lists a degree to port. What are the trade-offs of locating part or all of the house bank perhaps under a settee forward? To get it done would require nothing more than some new longer cabling of the proper AWG. Without measuring I suspect that would be 2 AWG
basic battery connections question
- Thread starter George Braun
- Start date
Assuming the new batteries would be wire in parallel to form a bank of 4 batteries, there is a lot of wiring that will need to be modified. When batteries are wired in parallel all of the connecting wires must be of the exact same length in order to charge and discharge them correctly. If the wires are of different lengths, the batteries with shorter connections to the charging sources and loads will charge and discharge faster than the more distant batteries. This has the potential to become a real rats nest of fat cables. There are ways to mitigate this, however, they entail some significant rewiring and system design changes.
Charging will also be an issue. How big is your charger? Is it a three stage smart charger? Currently you have about 200 ah of capacity doubling that will halve the charging current available to recharge the batteries. If you have a 40a charger, with 2 batteries each get 20a which is OK, with 400a each battery will only get 10a. Charging times will significantly increase. If your current charger is only 20a or 30a, it will take even longer. The alternators' output will also be divided between all the batteries, sharply reducing charge times.
In short, there will be significant rewiring to do to maintain an efficient system and longer charge times. The only upside will be greater capacity. Whether this is worth it really depends on how you use the boat and how you intend to use it.
Charging will also be an issue. How big is your charger? Is it a three stage smart charger? Currently you have about 200 ah of capacity doubling that will halve the charging current available to recharge the batteries. If you have a 40a charger, with 2 batteries each get 20a which is OK, with 400a each battery will only get 10a. Charging times will significantly increase. If your current charger is only 20a or 30a, it will take even longer. The alternators' output will also be divided between all the batteries, sharply reducing charge times.
In short, there will be significant rewiring to do to maintain an efficient system and longer charge times. The only upside will be greater capacity. Whether this is worth it really depends on how you use the boat and how you intend to use it.
For the reasons above plus others not mentioned, you would be better served using the 2 new batteries in a second separate bank charged independent of the old pair. This will provide a good compromise and the extra capacity desired with the least complications.
I agree with Don. Creating a second, independent bank is not only simpler, it allows redundancy. In the event of a failure in one bank, you can switch to the other bank and continue normal operation while fixing the fault in a unhurried manner rather than under pressure.
I can't speak to the technical issue but I have three group 27 agms in my house bank in the bottom of the port locker on my Hunter 356. Also a group 27 lead acid starter battery. I have charged both banks from the charger, once, but I usually rely on 200 watts of solar to the house bank.
The 2 bank system has advantages and disadvantages. It requires more conscious management of charging and the low charge rate when all 4 batteries are being charged remain.
Here's a good article on the system, sometimes referred to as the 1-2-Both switch system.
1/2/BOTH Switch Considerations
1/2/BOTH Battery Switch Considerations - Ever wonder how to make the 1/2/BOTH switch easier to use, let this article explain how to do that.
marinehowto.com
I'm going to be the contrarian here and say that the OP is a good candidate for converting to lithium, and that while the expense delta is not zero, it's not excessive either.
Given:
1 FLA start battery
2 FLA Grp 31 house batteries that weigh enough to cause a list. The OP doesn't say, but his bank is likely ~210AH, or 105 AH usable when new. He expressed a desire for more storage. He cannot easily expand the bank due to space limitations.
Options:
It's no longer the case that LFP is a lot more expensive, especially when you consider longevity. Replacing the house bank and charging from the start battery with a DC-DC charger is a pretty common solution.
Given:
1 FLA start battery
2 FLA Grp 31 house batteries that weigh enough to cause a list. The OP doesn't say, but his bank is likely ~210AH, or 105 AH usable when new. He expressed a desire for more storage. He cannot easily expand the bank due to space limitations.
Options:
- Extend the existing bank using some questionable or expensive wiring practices to a third battery
- Add 2 new batteries as a second bank.
- Ditch the FLA group 31's and replace with a pair of 100AH LFP batteries
It's no longer the case that LFP is a lot more expensive, especially when you consider longevity. Replacing the house bank and charging from the start battery with a DC-DC charger is a pretty common solution.
Op has about 180-200 Ah, of which about 100ah is usable. (Agm or flooded?)
A 280Ah .lithium pack costs $800-$1000
A dc dc 50A charger is another $300.
How much would adding 200ah of agm, plus re wiring both banks or new battery switch plus lost storage space cost?
Boost in capacity, less weight, minimal re wiring.... most agm chargers can charge lifepo4, so long as float voltage is 13.5 to 13.8v....or just let the dc-dc charger deal with dc and ac charging sources.
I know what I'd do....lithium can be done in stages.
A) LIFEPO4 with dc-dc as only charging source from starter batt
B) external alternator regulator, alternator now charges house batt, dc-dc reporposed to charge starter battery. New ac charger for house batt (maybe...)
A 280Ah .lithium pack costs $800-$1000
A dc dc 50A charger is another $300.
How much would adding 200ah of agm, plus re wiring both banks or new battery switch plus lost storage space cost?
Boost in capacity, less weight, minimal re wiring.... most agm chargers can charge lifepo4, so long as float voltage is 13.5 to 13.8v....or just let the dc-dc charger deal with dc and ac charging sources.
I know what I'd do....lithium can be done in stages.
A) LIFEPO4 with dc-dc as only charging source from starter batt
B) external alternator regulator, alternator now charges house batt, dc-dc reporposed to charge starter battery. New ac charger for house batt (maybe...)
LiFePO4 prices are not as high as quoted unless you insist on name brand - which from what I can see gains very little. The cells are sourced the same, the BMS is a 3rd party wired in, and a case is constructed around the battery. On Amazon, a 150AH LiFePO4 12V with Bluetooth (don't buy without) is less than $300, or $600 or less total for the bank. A Renogy 40A DC-DC charger is $140.
The costs for LiFePO4 came down so much that lead acid didn't make sense for me anymore. And my back and shoulders thank me very much for the switch.
Fred W
Stuart/ODay Mariner Sweet P
That price was for a mid-range brand, using a proven BMS with bluetooth and grade A cells..... SOK, etc..., not a rebranded bottom of the barrel here one day, gone the next label. Built from the factory, not assembled by the user! I have seen Renogy equipment fail on RVs often, I would not recommend it to a friend in a marine application where a loss of power would be very unpleasant!
Renogy for the most part rebrands other people's electronics, the one's I've opened up didn't have conformal coatings... to each their own of course.Agree that the cost of lifepo4 has come down so much that it doesn't really make economic sense to replace with lead, unless you just need a battery to sell the boat....Less weight, more time at anchor without an engine, longer lifespan, faster charging, price per usable Kwh almost matching or cheaper than lead. One doesn't have to change everything at once, a DC-DC charger is a great way to step into it step by step.
I included more than just batteries in my estimate. Upgraded fusing is essential. Likewise, cabling should also be given close inspection and evaluated against current ABYC standards. Drop-in batteries are often not, because there's always more to a safe installation. Here's a good primer on the topic: Drop-In LiFePo4- Be an Educated Consumer
My point was - and remains - the OP can convert for considerably less $$ than advertised. The arguments against the low ball estimate:
The OP doesn't want to make the change until his current batteries give out. I guess he is younger and sprier than I am, and can lift and place 60lb batteries with impunity. I can't.
Fred W
- cells may not be Grade A. I have yet to see any LiFePO4 battery advertised with less than Grade A cells. A few claim A+ cells. I would be suspicious of a battery that did not claim Grade A cells. As for A+ vs A, what does that mean in real life? No one is saying.
- I pointed out the Renogy DC-DC charger as that came up 1st in my Amazon search, and Renogy is a known brand name. A brand disdained by some, but others are quite happy with.
- BMS - the no-names use a stock BMS from another party, with few reported failures. The name brands design their own BMS. The BMS is the most likely failure point of a modern LiFePO4 battery. The result is the middle tier has the most problems with BMS failures or "features" that don't work correctly. LiTime is an example of this.
- Wiring is wiring. Either his wiring is adequate for the planned situation, or it is not. Any needed wiring upgrades are the same cost for either type of battery. The extra needed for a LiFePO install are fast acting circuit breakers, which I would want on multiple batteries of a lead acid install, too.
The OP doesn't want to make the change until his current batteries give out. I guess he is younger and sprier than I am, and can lift and place 60lb batteries with impunity. I can't.
Fred W