My Unusual (Alternate) Dual Battery Setup

[2nazt]

I'm having my fun tomorrow mounting the new batteries, switch and grill and then taking the ski out because I have off and the wife will be working! Ordering all my wire tomorrow from tinned marine once I mock up everything on the boat! Oh and switch out a bilge pump that burned out last outing.

 

[Bruce]

As for tinned wire, I installed off the shelf cables from Tractor Supply three summers ago. They are holding up great.

 

[2nazt]

Being only in Saltwater I worry from other horror stories. Would be way cheaper though.

 

[Bruce]

Being only in Saltwater I worry from other horror stories. Would be way cheaper though.

Mine have 26 days in salt. Not 26 salt water trips but 26 24 hour periods in salt.

 

[2kwik4u]

Going to revive a somewhat old thread here.

Wife has OK'd another upgrade of the stereo system this year. It will be a mild upgrade with (4) new speakers, (1) amp, and (1) 10in sub. Currently only have the factory stock head unit, Wetsounds Stealth 10 Ultra soundbar, and the rest of the factory loads.

With the new stereo I would like to upgrade the power reserves on the boat, but want to keep it as SIMPLE as possible. We currently run a single smaller battery and have never had any issues. I'm considering moving to two slightly larger batteries, and wiring them such that they are in parallel. The thought is that I don't care which battery I pull from at any given time, I just want a larger pool of energy to start with. I already have a single battery on/off switch, and this serves us well to keep stray loads down. We will be carrying a Li-Po jump pack with us, and on a single engine, reserve power is not really an issue.

The goal would be to get a good solid 8hrs of stereo run time at moderate volume levels, be able to restart and get the boat back on a trailer. Only a few times a year will the boat be left in the water overnight, and in those instances I can run an extension cord to the dock to recharge if needed. When at home the boat stays plugged in to a battery tender type device to keep the batteries topped off.

SO......my questions

@Bruce Can it be as simple as purchasing and mounting another battery next to my exisiting battery and connecting the posts togethor (in parallel)? That would be an ideal "simple upgrade" for me. How do I check that my tender is acceptable for the larger capacity? My thought is it will simply take longer to top off than before because the pool is larger. Correct?

@swatski You mentioned upgrading some time back in this thread (it's like 3yrs ago now). What did you end up doing? You have a pretty good read on getting the most value for your mods. I'm curious if you ever put the LVD in place.

Thanks to all!

 

[Bruce]

@Bruce Can it be as simple as purchasing and mounting another battery next to my exisiting battery and connecting the posts togethor (in parallel)? That would be an ideal "simple upgrade" for me. How do I check that my tender is acceptable for the larger capacity? My thought is it will simply take longer to top off than before because the pool is larger. Correct?

When running batteries in parallel (or in series) it is best to use similar aged identical batteries.

Depending on budget I would go with two new lead acid deep cycle batteries for the lowest cost, two new AGM deep cycle batteries for longer life or two new lithium batteries for the longest life and greatest usable capacity.

Lead Acid and AGM batteries should not be discharged below 50%. Lithium batteries can be discharged to 80%. A 100 amp hour group 31 Lead Acid or AGM battery provides 50 usable amp hours while the same capacity Lithium battery provides 80 usable amp hours.

My batteries provide 100 amp hours of usable capacity. That is around 1,200 watt hours. If I wanted to play music for 8 hours straight I would need the music system to draw an average of less than 12.5 amps or 150 watts. My systems peak draw is around 65 amps or 780 watts. I likely could run for 8 hours if I was very disciplined with the volume control but I not sure that I have that level of discipline.

I recently realized that my pair of AGM batteries has 5 summers on them and are still going strong.

 

[2kwik4u]

@Bruce Thank you sir.

Guess I need to get into researching what kind of power draw I expect from my Amp/HU/Bar while running.

Is stereo equipment power draw linear? i.e. does 75% volume mean 75% of peak power draw?

 

[Bruce]

@Bruce Thank you sir.

Guess I need to get into researching what kind of power draw I expect from my Amp/HU/Bar while running.

Is stereo equipment power draw linear? i.e. does 75% volume mean 75% of peak power draw?

Draw is quite variable depending on the music played.

Class D amplifiers will draw while playing with little waste.

You can use an amp clamp to determine the average draw while playing music.

Most if not all amplifier ratings are higher than the current they draw.

 

[FLJetBoater]

One interesting discovery is that that key switches are powered through the house load wiring. So you must have power to the house circuit to start the boat.

Is this the case in the 2014's? I recently bought a 2014 Yamaha 242 LS.

Last weekend, I had the boat out for quite a while at an island. Went to leave and the engines would not turn over. I was a bit shocked, as there is a DVSR between the house and start - how could the start have died?? I turned on the emergency parallel (it was off before) and it fired right up. I was never able to figure out what happened. By the time I got back both batteries were 100%. However, now I'm wondering if the emergency parallel actually sent power TO the HOUSE for the key switches, not from the house TO the START for the engines, which would 100% explain what happened.

 

[subysti]

@FLJetBoater if by the time you got back to the dock both batteries were at 100% I would say either a bad/loose connection, corrosion or bad batteries. These boats do not charge batteries well so unless it was a 6-7 hour drive back there is no way the engines would fully recharge a dead battery. What was the reading on both batteries when it would not start?

 

[FLJetBoater]

@FLJetBoater if by the time you got back to the dock both batteries were at 100% I would say either a bad/loose connection, corrosion or bad batteries. These boats do not charge batteries well so unless it was a 6-7 hour drive back there is no way the engines would fully recharge a dead battery. What was the reading on both batteries when it would not start?

I can't see it being bad batteries. I've been out a dozen times since, and zero issues with the batteries. It wasn't a 6-7 hour trek back, maybe 2 hrs, 30 mins at full throttle rest at no wake speeds. Unfortunately, I didn't have anything on me to check the voltage on the batteries when it wouldn't start.

But, how dead would a house battery have to be for the switches to stop working? Maybe not 100% dead. It's a dual engine so there's double the stator and I have not had to charge my batteries at all since then, and they're both at 100% right now (was last on the water yesterday).

 

[subysti]

House battery shouldn't have anything to do with the engines not starting unless somethings wired wrong. Thats the point of the house battery, it runs all the electronics so your starting battery never gets drained. Maybe wires got switched if batteries were removed at some point? How do you know the batteries are at 100% now. Have you checked with a DVM? Sounding more like a bad connection / grounding issue. I'd remove the battery connections and clean with a good battery terminal cleaner and the insides of the terminals. It may not look like there is corrosion but a film can build up and reduce the amperage getting through to start the engines.

 

[FLJetBoater]

House battery shouldn't have anything to do with the engines not starting unless somethings wired wrong. Thats the point of the house battery, it runs all the electronics so your starting battery never gets drained. Maybe wires got switched if batteries were removed at some point? How do you know the batteries are at 100% now. Have you checked with a DVM? Sounding more like a bad connection / grounding issue. I'd remove the battery connections and clean with a good battery terminal cleaner and the insides of the terminals. It may not look like there is corrosion but a film can build up and reduce the amperage getting through to start the engines.

There was someone who stated in an earlier message that the house battery powers the ignition switches. I don't know enough about electronics to know whether or not that would mean a dead house battery would prevent you from starting the engine? I think the switch sends a low voltage signal to the starter, which then fires but draws current from the starter battery. If the ignition switch can't provide that low voltage signal, the engine wouldn't start?

I have a 15AMP charger that I bought. When I hooked it up to the batteries it says that they are already at 100%.

 

[FLJetBoater]

My diagram may be confusing. My starter and stators are on the supply side of the LVD (before the LVD). Only the house (accessory) loads are on the load side of the LVD. This way my engines start normally regardless of the LVD's state.

From my perspective the two 20 amp fuses on the load side of the LVD limit the current through the LVD to 40 amps. The only reason to add a fuse between the switch and LVD would be if you were concerned about the LVD itself shorting and drawing more current than the switch could handle. I believe that scenario would be best handled by large fuses between the batteries and switch.

The Blue Seas m-LVD has a continuous amp rating of 65A. How likely would you be to exceed this in a 2 amp setting?

The wetsounds syn-dx6 I'm getting for the cockpit speakers has 3 30A fuses in it which tells me that it could draw up to 90A. Realistically, it's probably 900W @ 90% efficiency is drawing about 1000W. Music is usually a 50% draw, so 500W / 12V = 41A at full volume. I think for now, I'd probably be OK with the m-LVD but adding a set of towers & sub + new amp would more than double the wattage draw. I'll have to use an amp clamp to get a realistic draw before I add the 2nd one in there.

Should I just throw on a 60A inline circuit breaker before the m-LVD for now? If it's getting anywhere close to the 40A load from the single amp, would I need an LVD before each amp? Assuming they'd probably both just shut off at the same time anyway?

 

[Bruce]

@FLJetBoater, the m-LVD is rated for 115A for 5 minutes at a time.

I have two KAC-M3004 amplifiers and a 100 watt underwater LED. Combined they are over 52 amps max draw. I have never had a problem running that load for hours.

If your AMP(s) was / were constantly drawing 50 amps you would run down a group 31 battery every hour. At 90 amps a group 31 battery would last ~30 minutes.

Battery capacity is likely to be an issue before the m-LVD's capacity becomes one.

 

[FLJetBoater]

@FLJetBoater, the m-LVD is rated for 115A for 5 minutes at a time.

I have two KAC-M3004 amplifiers and a 100 watt underwater LED. Combined they are over 52 amps max draw. I have never had a problem running that load for hours.

If your AMP(s) was / were constantly drawing 50 amps you would run down a group 31 battery every hour. At 90 amps a group 31 battery would last ~30 minutes.

Battery capacity is likely to be an issue before the m-LVD's capacity becomes one.

That’s a bit scary to me actually. Those amps are 300W max. 600W for both @ max volume.
90% efficiency = 665W / 12V / 50% music draw = 27A. The 100W light would draw another 8 or so for 35A total. How are you getting 52A of draw? Or did you just straight divide the 700W by 12v which is 58A and use that as the max? But then you’re saying even with that max you can run for hours so they clearly aren’t drawing that much power?

 

[Bruce]

@FLJetBoater, the spec sheet lists the amps draw as 22. I estimated as 22 + 22 + 8 = 52.

You could connect all the electronics that you want to use, set them all to the level you would use and use an amp clamp to get a reading of the current draw.

I did check current after installing the amps in my boat and was comfortable with it. I have no problem running the amps and a refrigerator all day long with two group 31 batteries so as you point out the average draw is far less than the peak.

 

[FLJetBoater]

@FLJetBoater, the spec sheet lists the amps draw as 22. I estimated as 22 + 22 + 8 = 52.

You could connect all the electronics that you want to use, set them all to the level you would use and use an amp clamp to get a reading of the current draw.

I did check current after installing the amps in my boat and was comfortable with it. I have no problem running the amps and a refrigerator all day long with two group 31 batteries so as you point out the average draw is far less than the peak.

Ah ok. I didn’t look at the amp draw just at the possible watts, which was 75x4 =300 / 12V = 25. But good to know.

I think that is the only realistic approach, to hook everything up and put a clamp on and see what the draw is like.

For batteries, I’m debating whether to leave the starter as is and just replace the current house (old regular cell starter type battery) with 2 group 31s, or whether I should just buy 3 batteries and run a single bank with the m-LVD on the house side. The northstar nsb-agm31m can provide 1150cca which should be way more than required.

 

[Bruce]

Our engines are started by small batteries in waverunners. I would not worry about cranking capacity at all.

If you need the capacity go for three. If two are enough there is no need for a dedicated starter battery.

 

[FLJetBoater]

Our engines are started by small batteries in waverunners. I would not worry about cranking capacity at all.

If you need the capacity go for three. If two are enough there is no need for a dedicated starter battery.

If I go with 3 batteries in a single bank I'll probably run battery -> bus bar. Off the bus bar one line to each starter, one line to house side. Where should I circuit protect? Before the bus bar? If so, how many amps? If after, do I only need it on the house side or does the engine side need a circuit breaker as well?

Edited: nevermind, found the answer. Circuits from battery to starter are not protected but could draw significantly more power than the busbar ratings. So, I'll run straight from battery to starters and then from battery to busbar for the house and protect that side with a 150A circuit breaker before the busbar.