How many amps per hour driving?

davidathomas42

davidathomas42

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I know it’s subject to size of alternator and day/night wipers on a/c etc etc.

But as a rough estimate has anyone done any tests on how much power an hour of driving will throw in your leisure battery?

I’m sat off grid currently for my 2nd night after an hours drive from this morning pulling 3amps with TV on and a few lights. Battery showing 12volts down from 12.8 parking up a few hours ago.

Just seems a bit low given a plus temperature and a brand new battery. 115amp size.

2 nights ago was on EHU so should have been fully charged. I have a single solar panel too.
 
There are too many factors to even guess. If you have a B2B charger, however, it is easier. It will put as many amp hours into your battery as it is rated in amps. At least until the bulk phase ends when it is nearly full. If you have a split charge, it could charge at anything from 1A to 60A, depending on multiple factors.
 
Have you checked that the battery is actually being changed?
 
Won’t the regulator in the alternator discharge any excess power once the batteries are charged to stop them being overcharged?

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Yes, very variable, but to pluck a figure out of the air I'd say 20A would be typical if the battery needs charging. By the way, it's either '20A' or '20 Ah per hour', not 'amps per hour'. Although many will get half or double that.

So if the draw is 3A, an hour's driving should give you enough for nearly 7 hours. How did you find the 3A figure? If it's an amps meter, does it show the input amps to the battery when the engine is running?
 
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I doubt an hours drive will put much into the battery, most battery monitors will read lower than the battery is during use....it may read 12v now but would probably jump back up a long way when you switch everything off
 
Pausim said:
Also depends on how well wired the motorhome is. Far too many have long runs of thin wire and the charge is limited by the resistance.
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It’s a Bessacarr 640 2011 so I guess ok standard but not awesome
 
With a Schaudt EBL119 - i think you get something like 18A when driving - however with a lead Acid / AGM habitation battery, the ability of hte battery to absorb current tails off significantly once you reach about 80% and the final 20% can take some time.
with a lithium battery and a 50A B2B, i get 50A through the charge profile…from empty to full

so to put 100Ah back into a AGM Battery using the EBL would take something 6-8 hrs driving vs 2 hrs with a 50A B2B

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When you parked up and looked at the 12.8V the battery was probably still settling down from receiving a charge. A true measure of the charged voltage would be seen after resting for 0.5 to 1 hour. 12.6 perhaps 12.7V depending on gauge accuracy would be a fully charged lead-acid.

Remember too that for lead-acid / AGM type batteries you can use around 50% of your 115Ah.

As many have said, the standard relay charge on your van may not give you as much as you expect. My vans standard Sargent PSU thing only does 12A max, and I suspect I never got that due to resistance and other stuff. Hence a B2B as I upgraded the pathetic 75Ah supplied hab battery to lithium. Even if I were to get 12A on the 75Ah I'd have needed at least a 3 hour drive to get close to putting that 50% use back.
 
davidathomas42 said:
It’s a Bessacarr 640 2011 so I guess ok standard but not awesome
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That's the problem you have a Brit built van notorious for undersize wiring.
If the battery is down a bit you will get 10 maybe 15 amps on startup after about 10 min as the battery voltage rises it will drop to around 5 - 7 amps. Takes a least a 300 mile drive to fully charge couple of leisure batteries.

If you don't want to go to expence of a B2B you could increase the size of the wiring to both sides of the split charge relay. Depending on length of cable run use 16mm sq or 25mm sq cable, you will probably need to change the relay for a higher power one.
Doing that will increase the initial charge current to around 25 amps dropping off to 12-15 amps.
 
Lenny HB said:
That's the problem you have a Brit built van notorious for undersize wiring.
If the battery is down a bit you will get 10 maybe 15 amps on startup after about 10 min as the battery voltage rises it will drop to around 5 - 7 amps. Takes a least a 300 mile drive to fully charge couple of leisure batteries.

If you don't want to go to expence of a B2B you could increase the size of the wiring to both sides of the split charge relay. Depending on length of cable run use 16mm sq or 25mm sq cable, you will probably need to change the relay for a higher power one.
Doing that will increase the initial charge current to around 25 amps dropping off to 12-15 amps.
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Don’t mind any costs really that make the van better. I purposely spent £30k on a van with a budget of £50-60k so I could get a layout I really wanted and then do upgrades to systems and interiors etc. so far dropped £7k in the van with a healthy budget left. I want the van to be perfect for me and still cost less than a new one that needs everything doing.

That’s a long way of saying what’s B2B in a nutshell then?
 
davidathomas42 said:
That’s a long way of saying what’s B2B in a nutshell then?
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Battery to Battery charger allows you to charge the battery at a high current, you can get them in various sizes 30 amp, 45 amp, 60 amp & 80 amp.
I wouldn't go above 45 amp unless you are sure you have an uprated Alternator, I think the standard Ducator Alternators vary between 90 amp to 110 amp but converters often fit uprated ones, Hymer for example fit a 160 amp.

Manufacturers to look at for B2B, Votronic, Victon, Sterling, Votronic & Victron are the better ones.
 
busbuddy said:
most battery monitors will read lower than the battery is during use....it may read 12v now but would probably jump back up a long way when you switch everything off
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This! To get a true reading, use the battery for a while. Then switch everything thing off and allow it to settle. Then check the voltage. You will find it will rise a surprising amount after a short period of non usage over a reading taken when in use.

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davidathomas42 said:
That’s a long way of saying what’s B2B in a nutshell then?
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I bought one of these.
Basically they lie to the alternator and keep the batteries charging way above the Fiat starter battery regulator cut off

sterling-power.com

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We had this problem. Solar panels and ehu no problem. But no charging when driving. Long (very!) story short, it came down to corroded cables between alternator and starter motor. Had them replaced (£120, they are 1.2m long and thick) and now happily charge at 20-30A when driving (and the fridge works!).
 
Robert P said:
We had this problem. Solar panels and ehu no problem. But no charging when driving. Long (very!) story short, it came down to corroded cables between alternator and starter motor. Had them replaced (£120, they are 1.2m long and thick) and now happily charge at 20-30A when driving (and the fridge works!).
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I'll have to have a look next time the batteries are low and see what the altinator is putting in with the engine running and driving. I checked this week when I got back what the EHU was throwing in and it started just over 10amp which I guess will be the limit anyway from a 13amp house plug. after 4 or 5 hours it was pulling 5amps then later that night 1.75amps there about's which I guess was the past 80% charge state slowly topping off.

Fridge seems to operate ok while driving (y)
 
davidathomas42 said:
checked this week when I got back what the EHU was throwing in and it started just over 10amp which I guess will be the limit anyway from a 13amp house plug. after 4 or 5 hours it was pulling 5amps then later that night 1.75amps there about's which I guess was the past 80% charge state slowly topping off.
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Where were you measuring that? If it was 10A going into the battery then it's quite a lot lower than I would expect for a fairly low battery.

For information, a 13A house plug is at 240V from the house mains. It can supply 13 x 240 = 3120 watts. Converted to 12V power, it's still 3120W, but the amps is 3120 / 12 = 260A. So it would have no difficulty supplying 10A, 20A or even 200A to the battery if required.

I don't know what brand of EHU charger your Bessacarr has, but I'd imagine it is a 3-stage intelligent charger, probably 15 or 20A. It should push out its full rated output, whatever that is, from the start until the battery is about 80% full. If it doesn't there's something wrong somewhere.

Can you measure the battery voltage while it's charging, with a multimeter. You need to know if the full voltage is getting to the battery, or if it's being lost somewhere along the wiring.
 
Just another endorsement for a B2B. Even a 20-30min. run gives us enough re-charge for a day or two in our two 90Ah batteries.

We never use EHU and move every 2-3 days.

Since we fitted it 6-7 years ago I have never really thought about battery use - peace of mind.

I do not know why MH builders do not -

a) order big alternators when ordering the van chassis

b) do not fit B2B as standard

because the standard van alternator/regulator/engine battery set-up was never designed to cope with charging domestic batteries, which are required to feed several 12v systems over a long period, as opposed to van systems which are mostly required to produce the heaviest draw(lights, heater etc) when the engine is running.

Geoff

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It might help you to measure the current going into either the leisure battery or vehicle battery with a clamp type meter before you decide on your course of action.
This may provide useful diagnostics.
 
Lenny HB said:
Most German manufacturers do.

Vans with smart alternators have then or the leisure battery wouldn't charge. Mercs from around 2014, Fiat from around Sept 2019.
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Our 2021 pilote (fiat) had the new smart alternator but no B2B , drove 4 hrs & leisure batteries flat , when driving the fridge was draining all the power out , they retro fitted a 25a B2B , seems pilote hadn’t realised the affect the smart alternator was going to have , must have been hundreds slipped through
 
Robert P said:
We had this problem. Solar panels and ehu no problem. But no charging when driving. Long (very!) story short, it came down to corroded cables between alternator and starter motor. Had them replaced (£120, they are 1.2m long and thick) and now happily charge at 20-30A when driving (and the fridge works!).
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Good point (y) On my Fiat X250 van, the cable route is Alternator > Starter motor > Contact board > Starter battery +'ve.

The Starter motor is located on the front face of the engine, so exposed to the elements. Corrosion (or leakage to earth) where the two cables join at the Starter motor is possible.

Also, the earth return between chassis/engine block (braided strap) is known to corrode. I've replaced mine with a battery cable from Halfords.

A sign of problems in this area can be if the starter motor is sluggish in operation.
 
I have a later bessacar but to be honest, didn't want the hassle of keeping an eye on the power situation. So had a chat with Vanbitz and
took it down to them and had the whole system upgraded and an additional 150watt solar fitted with lithium batteries, no issues since.

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3-way fridges pull a lot of amps whilst on 12 volts. If the fridge is running, there can often not be a hell of a lot left for the leisure battery.
 
Guigsy said:
3-way fridges pull a lot of amps whilst on 12 volts. If the fridge is running, there can often not be a hell of a lot left for the leisure battery.
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Look at the lable on the fridge and check the rating for 12v. I have the dometic large fridge and that is 172w on 12v. That equates to 14A needed to run it. Does not leave much power for battery charging from the engine. Most van now seem to assume that EHU is normal, water and van heating run off 240v, fridge runs off 240v and now an electric ring is also being included.
 
SSILVO said:
I have a later bessacar but to be honest, didn't want the hassle of keeping an eye on the power situation. So had a chat with Vanbitz and
took it down to them and had the whole system upgraded and an additional 150watt solar fitted with lithium batteries, no issues since.
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Your reading seems perfectly reasonable - a battery of that size drawing 5 Amps from fully charged, would realistically be totally flat (10.7volts) in 10 hours.
 
snoozer said:
Look at the lable on the fridge and check the rating for 12v. I have the dometic large fridge and that is 172w on 12v. That equates to 14A needed to run it. Does not leave much power for battery charging from the engine.
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Agreed, my fridge is the same, and draws 14.4A. But a (non-smart) alternator will supply up to 90A even for a small one, mine on the Hymer is uprated to about 160A,I think. It regularly supplies 69A to the 70A B2B, as well as charging the starter battery and running the lighting, wipers etc. There's plenty of headroom for powering a 30A B2B even on a standard alternator. The problem is usually the thin wiring that restricts the amps to the leisure battery.
 
How do I know if our Carthago has a 'uprated' or 'smart' alternator? Do I just ask it hard questions? :giggle:

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