SO 35 - Additional batteries

[irlontop]

The So35 seems to come with 2x 100ah leisure batteries and then 1 starter battery, 

They are located in the aft starboard cabin on the SO35 (2cabin version)

It looks pretty tight in there, has anyone modified it to fit 3 house batteries? or even 2 larger batteries, I think the current space is 250 x 170 x 225high.

[puravida35]

My previous boat was a 2005 SO35 2 cabin layout with the extra battery option from factory. I might be mistaken, but I seem to recall an extra battery was placed under the floor of the port storage locker (in the space that would have been the 3rd cabin).

[Don Reaves]

I replaced the two houses batteries in my S0 35 with a couple of golf cart batteries. The 6 V batteries have quite a bit more capacity than the original batteries, and they fit in the same boxes. They are a little taller but not too tall for the available space.

[irlontop]

Thanks Don, 

Any idea what AH golf cart batteries you went for. 

Was there any maintenance on the golf cart batteries? topping up water etc? 

Thanks again, 

[Don Reaves]

The golf cart batteries I bought most recently (second set) can be seen using this link. The amp-hour rating is given for various loads, so I'll let you decide which one to use. At 5A, it's 157 AH.

These are wet cells with caps. You need to keep the electrolyte up just like for other wet cells.

Don

[iancymru]

On my SO33i I have 3 house batteries, the boat standard fit was 1 house batt. and 1 start batt. These we stowed to stbd. under the bunk in aft cabin, they were both 80amp batteries. I opted for the optional second house battery which was factory fitted under the aft bunk but offset to port against the port cockpit locker this was the same type 80amp battery as per the others. I decided I needed more battery power and got a third house batt. the same as the others which fitted just next too and aft of the second house batt. to port, I screwed a batt. box to the wooden frame below the bunk and drilled a hole through to run the wire, its pretty tight and no room for the battery box lid. Its not ideal as I have different lengths of wire between the three house batteries but the 3 x 80amp works for me but in the UK do not run the fridge for too long without the engine running. Ideally I would like to have had 2 x 100amp batteries for the house but its tight on space height wise under the bunk close to the centreline.

[MalcolmP]

Bit off core topic, but related.

As well as my 39i I also have a campervan with an single 90aH or so domestic house or habitation battery, which I had been planning to add an additional to double capacity.

BUT camper forums say that because of likely low capacity wiring, undersized mains battery charger as well as likely poor cabling from the standard engine alternator then there is a high risk that simply doubling the battery capacity will result in the new batteries never becoming fully charged. More conceningly is that the alternator wiring could become overheated, as may the mains charger as neither are designed to try to charge up double the battery aH capacity.

Any views?

[rene460]

Hi Malcolm, if you had not said campervan, it would look like the same question often asked about boats. Obviously a terminology difference in your neck of the woods, it sounds like you are talking about a motorised vehicle we would call a motor home, rather than one towed behind a standard vehicle, but the issues are very similar. I totally agree that one typical battery is not enough to run accomodation overnight for anymore than lighting and a radio, perhaps charging a phone or two. As soon as you try and run a fridge, you need the extra battery.

First, automotive wiring is nearly always based on wire overheating limits and not voltage drop, and anything beyond the engine bay starts to see that drop if there is much current drawn. You are probably not only charging the battery, but also running the fridge. A compressor fridge draws about 4 amps when running and perhaps runs about fifty percent of the time. An absorption fridge, as fitted to most land based caravans or motor homes is much worse, usually about 10 amps and not interrupted any time by a thermostat. Definitely only suitable for running when the engine is running, and you would not be the first to flatten the car battery over a longer lunch stop.

Typically here we have an auto electrician fit an extra quite heavy wire (up a gauge or three from the standard) with a heavy duty fuse and a voltage sensitive relay to only connect to the fridge when the engine is actually running. You would also run your house battery charger from this wire.  It is a quite separate addition to the normal trailer wiring.

When it gets to charging from the car you may need a dc-dc battery charger to boost the available voltage to the roughly 14 V needed for battery charging, and use it for both house batteries. Much the same as some owners have fitted on their boats for bow thruster batteries.

For the mains charger, it should be possible to find the specifications on current capacity of the installed unit, to confirm if it is enough. Otherwise you could replace it with a modern multistage charger of sufficient capacity. The best RV chargers are designed as a stand-alone regulated power supply, which does not even need a battery to power your equipment when plugged in. However the simpler systems have a normal charger connected to the battery to keep charging while you are using the 12V.   Main disadvantage to this is that you must have a battery to stabilise the voltage otherwise you may damage sensitive devices. And just like a boat, a solar panel or two on the roof, possibly backed up by an additional portable panel that you can move to face the sunshine you are parked, will extend your off grid time enormously. Oh, and when you are parked for any time, run that absorption fridge on gas, but not while driving.

Just my suggestions based on 40,000 km of caravan towing in this country. But exactly like a boat, except for those absorption fridges.

Rene460

[MalcolmP]

Hi Rene460

Thanks for detailed reply, all your assumptions are correct. Small RV equals motorhome/camper here in UK.

Absorption fridge, but that also runs on propane or mains and automatically disconnects from 12v when engine is not running.

I will be fitting solar which at least will be good in Spain, but much less so in UK 🤨

The wiring I can see to the domestic battery is very lightweight so will upgrade as much as possible, especially the earth. When the engine is running think there is only 12.4v or so getting to that battery so must be quite a loss in the wiring. I will check later what I am getting to the starter battery and also the voltages when on the battery charger.

The charger itself looks pretty Mickey mouse, no maker info apparent, but I would be surprised if more than 10 amp.

I am pondering if one simple solution would be when I add the second house battery to also fit a change over switch, IE both/1/2/off type. Then never use the both setting but simply regularly switch between 1 and 2.

Whilst I recognise that relies on me remembering to do that, at least should not overload the alternator or wiring.

I will also look at upgrading the mains charger, but the factory unit is multifunctional and integrates all the fuses as it is used as the distribution board, so not that straightforward....

[rene460]

Hi Malcolm, I had read that the newer fridge units had that automatic disconnect on the 12V when the engine is not running, but mine must be a cheaper model. Hence the VSR in the car engine bay.

Interesting that you mention the mains charger incorporating fuses and distribution, it sounds very similar to the one in my van. It is a Setec brand unit and I have the manual covering the 20 and 35 amp models if it is of any help. I could scan it and send it to you. Mine certainly accepts an input from the car, but no step up circuitry to help with any voltage drop from the engine, or other charge controls for when connected to the car 12V system. The manual says it expects 13.8 V input.  A new wire from the battery, with appropriate fuse would help eliminate that voltage drop.

I think I would add a separate simple mains charger for the second battery rather than the three way switch, but I guess I would eventually miss switching over and end up with a flat battery. Especially during storage when a periodic top up or at least a trickle charge is a good idea. Our previous boat was trailerable, and the battery suppliers always recommended a top up each three months. I installed a power point over the boat in the carport and never had battery problems.

Just one other thought, your original question was about whether the battery would ever be fully charged with the low voltage available from the car. However, it is not really very important. The main charger is actually the mains charger, which should have some sort of intelligent cycle. The car system is really only to keep the batteries topped up while driving, and if you normally camp in formal camp grounds with site power available, it is hardly necessary. The fridge should run from the car only when set to 12V, not from the house battery. At least that is the way they are normally wired here. Our battery is only charged from the mains charger or the solar panel, it is not connected to the supply from the car. I doubt that the solar panel would ever charge it up fully if it was really down, as it is mounted horizontal on the roof, so is only near optimum angle to the sun for a few hours each day. As we know from our boating experience, it is quite hard to get enough power from solar to supply the fridge, but the advantage of that absorption fridge is that you run it on gas when camped if you have no mains power available. So the solar or car alternator only has to top up to supply lights and phone charging. With LED lighting, it is not much.

Certainly a motor home or caravan is a great life, it’s a pity they don’t float very well. I guess you pass through very different countryside to what we see on our travels.

Rene460

[MalcolmP]

Apologies all for drifting this thread from SO35 towards RV Campers, as an admin I know I should know better...that said it is still directly relevant to keeping batteries in good order whichever vehicle or boat.

Many thanks again Rene460 for your professional knowledge on this.

I did some checking on voltages, and it seems the wiring and the charger may not be as poor quality as I initially feared.

Domestic

14.10 v on mains charger

14.0v on alternator

Dropped to 13.8v after 1 hour

Starter battery 12.4v after standing overnight in cold say 2 degree's

14.2v with engine running

The domestic and starter batteries are at least 4m apart so not too much voltage drop.

I do use the camper, off grid quite a lot especially in France and Spain, so cannot rely on 240v regularly. The solar will help, have yet to measure physically what can fitted.

I am still thinking that have a selector switch will allow me more flexibility in keeping 2 batteries for domestic use in as good order as possible depending on what power options is available.

Malcolm

[rene460]

Hi Malcolm, it sounds like you are in good shape, despite your initial fears.

Just shows you can’t take as Gospel everything you read on a forum!

Keeping batteries in good shape sounds pretty relevant to me, even if strictly slightly off topic for this thread.  Sometimes looking at a topic from a slightly different point of view reveals additional understanding.

Also, you deserve the highest praise for your moderation efforts, this has always been a very friendly place to hang out.  The odd friendly diversion just shows we are real people.  Only Siri stays right on strict topic, and we can all do without that.

So, well done and thank you for a great forum.

rene460

[irlontop]

Nov 27, 2018 14:57:34 GMT Don Reaves said:

The golf cart batteries I bought most recently (second set) can be seen using this link. The amp-hour rating is given for various loads, so I'll let you decide which one to use. At 5A, it's 157 AH.

These are wet cells with caps. You need to keep the electrolyte up just like for other wet cells.

Don

Thanks Don, 

Did you replace with 2 x 6v golf cart batteries?

I'm trying to find some space to fit 4 of them, proving a bit more difficult. 

on another subject, did you have any solar on your SO35? 

Thanks

[Don Reaves]

I have only 2 6V golf cart batteries, and no solar. I typically day sail and do short cruises to places that have power. So far, I haven't needed solar.

[ForGrinsToo]

I replaced the two parallel 75 Ah (for 150 Ah nominal, but you can only use 75 with lead-acid technology) with two 220 Ah 6 V in series for a 50% increase in capacity. They still fit into the original battery well on the 36i. Yeah, that's a modest increase but sufficient for our needs. Generally, we're running the engine 1 - 2 hours/day (entering and leaving anchorages) and getting as much out of a 110W solar panel as we can with angle of heel and shading. So one thing to do is look carefully at 6V while another is to go to LiFePO4 which have much greater usable capacity in a similar size, but you'll need to change the charging profile. That's likely our next step.


Geoff