How Big A House Battery?

[bigsapper]

I ordered a 100Ah LifePo4 for a house battery. Thing is huge and ways almost 25 lbs. How big a battery do I really need? I think the longest we've sat at anchor is about 3 hours and just running the factory radio and a Garmin 4 fishfinder.

Ok, did some quick research and math...
I = P/V

Garmin 43cv:
500w/12v = 42a

Jensen JMS32:
160w/12v = 13a

42a+13a=55a

So I should be able to get away with a 50Ah battery?

 

[FSH 210 Sport]

If the load is 55 A, in theory that’s less than two hours of use out of a 100Ah LiFePO4 battery.

Are you sure about the load of your Garmin? Usually these units are fused at 5A. 5A at 13.6 V is roughly 68watts.

 

[bigsapper]

That's the published spec for both devices. Probably "max" but not sure how to measure typical "run time".

 

[84rzv500r]

I run 3x400w amps and the head unit for 7-8 hours on a pair of 100Ah LiFePO4 Ampere Times in parallel.... doesn't drop the voltage more that 1/10th of a Volt...
this is at modest listening levels....

to measure Amps in DC ya have to inline the meter or get a Fluke with a Hall effect clamp IIRC...

 

[FSH 210 Sport]

That's the published spec for both devices. Probably "max" but not sure how to measure typical "run time".

What size is the fuse that feeds the Garmin unit?

 

[lazergeek]

Here is the current draw from Garmins website for that model. The 500 w is in the Sonar section so not applicable to electical draw.

 

[lazergeek]

With the correct Garmin draw of 2 amps your at 15amps total per hour so with your your 100amp battery discharging to 20% you will get 5-6 hours at max draw. 25 pounds for a 100 amp battery is still less weight then your lead acid start battery.

 

[fatboyroy]

i have garmin 743xsv and stock radio. Been on fishing trip with radio and fishfinder running 6 hours straight on stock house battery and did not get low battery warning. 100AH battery is a lot, but if you have the means, you could never have enough power, the more the better.

 

[bigsapper]

Thanks for clarifying that for me. Looks like I can easily get away with a 50Ah battery.

 

[FSH 210 Sport]

Yeah but why would you?

The typical 100 Ah LiFePO4 battery weighs 30#. The lead acid equivalent weighs roughly 60# and only has 45Ah of capacity, while the LiFePO4 has 80Ah at an 80% discharge.

Your lead acid start battery, if it’s a group 24 weighs about 45#.

Just be sure your battery charger is correct for the LiFePO4 battery

 

[bigsapper]

https://www.amazon.com/gp/product/B08G3STB1N/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[FSH 210 Sport]

So, here’s the next thing you will possibly need to do.

If you have the oem dvsr or other vsr you will probably need to make it either a manually activated dvsr or one that is activated by the ignition hot. Here’s why, the LiFePO4 batteries resting voltage is 13.6 volts which is .4 volts above the dvsr engagement point.

You do not want the dvsr to parallel your LiFePO4 battery when the engine is off. Otherwise it will start discharging into your lead acid battery due to potential difference between the two batteries.

See my LiFePO4 battery upgrade thread here:

https://jetboaters.net/threads/conversion-to-lifepo-batteries.35834/

 

[bigsapper]

Thanks for the link. I've parked this project until I can do more research. Just discovered I'll probably need to upgrade the charging system (alternator).

 

[lazergeek]

Thanks for the link. I've parked this project until I can do more research. Just discovered I'll probably need to upgrade the charging system (alternator).

There is not much you can do on the engine charging side. The boats have stators not alternators so limited output from the motors. Most just add a Norco to charge from the house and call it good.

 

[Beachbummer]

The engine's electric output is not terrible, but you need run time to recharge. If you putter for 20 minutes and listen to music for 6 hours it will catch up. Alternator or stator.

It's a good idea to recharge as suggested, specially if engine time is short and listening time is long.

Best of luck!

 

[BoatElectricians]

I ordered a 100Ah LifePo4 for a house battery. Thing is huge and ways almost 25 lbs. How big a battery do I really need? I think the longest we've sat at anchor is about 3 hours and just running the factory radio and a Garmin 4 fishfinder.

Ok, did some quick research and math...
I = P/V

Garmin 43cv:
500w/12v = 42a

Jensen JMS32:
160w/12v = 13a

42a+13a=55a

So I should be able to get away with a 50Ah battery?

I ordered a 100Ah LifePo4 for a house battery. Thing is huge and ways almost 25 lbs. How big a battery do I really need? I think the longest we've sat at anchor is about 3 hours and just running the factory radio and a Garmin 4 fishfinder.

Ok, did some quick research and math...
I = P/V

Garmin 43cv:
500w/12v = 42a

Jensen JMS32:
160w/12v = 13a

42a+13a=55a

So I should be able to get away with a 50Ah battery?

You are using 55Amp x 3 hours = 165AH
Order a 2nd battery ?

The project is more complex:

No not connect your currently installed Lead Acid batteries, nor your alternator DIRECTLY to the lithium battery use a Dc/Dc converter beside the lithium batteries.
Battery charger for the lithium batteries has a different characteristics

in addition, your alternator MUST NOT be disconnected from the lead acid battery, while the alternator is running, that will burn the alternator.
Lithium batteries have ann internal BMS ( Battery Management System) that self disconnect the battery if over/under charged, and over/under temperature specs.

Lead acid batteries do not self-disconnect, they remain connected to the alternator.



Miami BoatElectricians