Electric Water Pump - Power Draw

[LD334]

I'm considering fitting a Davis Craig EWP80 kit, including an electric fan. It looks like the ampage is 7.5A for the pump and similar for the fan.
The car is fitted with an alternator from a Mk 2, all of the smaller bulbs are LED and I've fitted halogen headlamps. I'm wondering if there are any electrical upgrades required?

[mole42]

I run a 220W (18Amps) fan and two Cibié 55W spots off the 18ACR alternator with no modifications. All the other lamps are standard, except the reversing lights which are LED.

No problems for me, but the fan and the lights are not used for very long periods and rarely together!

[greystag]

electric water pump

I'm considering fitting a Davis Craig EWP80 kit, including an electric fan. It looks like the ampage is 7.5A for the pump and similar for the fan.
The car is fitted with an alternator from a Mk 2, all of the smaller bulbs are LED and I've fitted halogen headlamps. I'm wondering if there are any electrical upgrades required?

are you sure thats the correct pump I run there pump and controller and it is an ewp 115, recommended for a v8 , come back to me if I can help.
Regards Terry

[Stagsongas]

I'm considering fitting a Davis Craig EWP80 kit, including an electric fan. It looks like the ampage is 7.5A for the pump and similar for the fan.
The car is fitted with an alternator from a Mk 2, all of the smaller bulbs are LED and I've fitted halogen headlamps. I'm wondering if there are any electrical upgrades required?

LD334,

Required is not quite how I'd put it, but it is more about how you feel about the potential risk. My personal thinking is that the more load there is on the Battery after the engine and alternator have been stopped, the more likely it is for me to get that awful 'Click' when hoping to start the engine once more.

With the fan and EEWP running on after engine stoppage (as they do), and doing so for more time on a hot day, it may be asking for more than the standard Battery can cope with, especially if it is not right up to par. I've fitted a much larger Battery to compensate. There is no doubt higher output alternator is also a good move, but that can only put in as much power a Battery can store, and if it's a small one (like the Stag has) it will not be the same as having a standard alternator charging up a larger Battery with more capacity to store that power. That's why I've gone for the larger Battery first.

Don't mistake me for saying that upgrading the Battery is the only thing to do, there is no doubt that upgrading both the Battery and the Alternator is the best way of ensuring there is enough power to run the car and all it's add-ons, and to provide comfort that the fan and EEWP can run on as long as they like and you'll still be able to crank the engine to go home after a good day out.

Naturally, as we tend to add more things that use power in our cars these days (Sat-Nav, Phone Chargers, ICE etc. etc.) the original system has far less margin, and for me an increase in both power generation and storage is one way to ensure the car gives better reliability, even if only by it being ready to start every time without any worries.

Or you could just take a flyer and do nothing.....but you have doubts on that as you've raised the question!

Regards

Steve

[mjheathcote]

There is no doubt higher output alternator is also a good move, but that can only put in as much power a Battery can store

That is true with no load, but under load with the engine running the alternator takes the load up to its power output, then the battery makes up the shortfall and starts discharging.

So with pumps, fans, lights on etc, with the standard setup the standard alternator can't take all the load, the battery starts discharging, and the voltage drops. What is going in is less than what is going out.
Fit a higher output alternator, and it can cope, the battery does not discharge.
What is going in meets what is going out.
The only benefit for a larger battery is when you have load and the engine is not running, pump and fan running purely off the battery.

[Staggard]

That is true with no load, but under load with the engine running the alternator takes the load up to its power output, then the battery makes up the shortfall and starts discharging.

So with pumps, fans, lights on etc, with the standard setup the standard alternator can't take all the load, the battery starts discharging, and the voltage drops. What is going in is less than what is going out.
Fit a higher output alternator, and it can cope, the battery does not discharge.
What is going in meets what is going out.
The only benefit for a larger battery is when you have load and the engine is not running, pump and fan running purely off the battery.

+1

[mjheathcote]

+1

Yes and why racing cars replace the heavy high capacity battery for a small capacity light weight one.
When its started (sometimes with jump leads on single seaters) the battery is hardly required, the alternator does all the work.

[Staggard]

Yes and why racing cars replace the heavy high capacity battery for a small capacity light weight one.
When its started (sometimes with jump leads on single seaters) the battery is hardly required, the alternator does all the work.

Racing bikes don't have a battery at all. most are started on rollers

[mjheathcote]

So I would upgrade the alternator first, battery second!

[Staggard]

So I would upgrade the alternator first, battery second!

Absofeckinglutly

[mjheathcote]

http://www.wosperformance.co.uk/media/uploads/files/2/wosp-web-brochure.pdf

See page 14.

You could say Wosp are the king of alternator porn!

[marshman]

Steve does raise a very valid point. A "standard" 072 battery has capacity of up to 70 AH. This is at what is known as the 20 hour rate, i.e. a rate of discharge that will exhaust the battery in 20 hours. So in the case of an 072 a current draw of just 3.5A over 20 hours. However, if you discharge a car battery over about 35% this is regarded by the manufacturers as a deep discharge and damages the battery (reduces its capacity and shortens its life) and if this is followed by a rapid, high current charge - i.e. from your alternator - it is likely that further permanent damage will result. So your 70AH capacity battery really has a usable capacity of about one third of that stated so about 23AH. Now if your electric fan takes say 15 amps or so (some take more and some take less) and your electric water pump takes 7.5A (taken from a post in this thread) you have a current drain of approaching 23A. The battery can supply this for an hour. BUT you turn up to a show on a nice hot summers day, park up and switch off the engine. The fan and pump do their job and run for maybe 10 - 15 minutes if it is really hot. You then sit there all day, radio playing, doors open so interior lights on, then at the end of the day start the car. I would wager that the total discharge of the battery under these conditions is more than 35%, the alternator will fast charge the battery which adds to the damage the deep discharge has done. The battery will appear to be fine but each time you do this you significantly shorten the life of the battery until one day its capcity is reduced to the point the car does not start. It is also worth noting that a lot of battery specifications are measured at 25 deg C, The under bonnet temperatures are a lot hotter than that which will derate the battery further.

With regard to the alternator output a standard 18ACR output is iirc about 45amps. The electrical load could be made up as follows:

4A ignition
7.5A water pump
2A petrol pump
10 A radio
15A cooling fan
20A main beam lights

Total 58.5A which is 13.5 more than the alternator can supply, so as has been said the difference comes from the battery, which will supply this for around 2 hours. BUT how often would you drive for 2 hours straight, at night, in temperatures that require the cooling fan to be permanently on? The scenario of going to a show and draining the battery is more likely for the majority of classic car owners/users. Yes if you upgrade you in car entertainment, fit cibie mega lights etc. you need to upgrade the alternator but you also need to check and possibly upgrade the wiring as well.

Conclusion? Don't just dismiss the requirement for a larger capacity battery over a higher output alternator. As with so much in life it depends on individual circumstances. Correctly sized, charged and looked after modern car batteries last many years, they usually only die because they are abused, often unknowingly, by their users.

All the above is my personal opinion with a few scattered facts from various sources. No batteries or alternators were abused in writing this post

Roger

[flying farmer]

I am running an EWP on my Rover V8 engined Toledo. Don't bother with anything bigger than the basic EWP 80, it cools the Rover engine with 207bhp, and my Stag engine with 246bhp perfectly adequately. I also did over 100 miles on flat out on a track day at Castle Combe in my stag engined TR yesterday which also uses an EWP 80.

The problem I have found with the electric controller is it does not like low voltage. When the volts drop below about 12V the controller lights up like a Christmas tree and goes into fault mode so it automatically turns on to continuous pumping rather than the 10 seconds in every thirty that it normally runs at when working at normal temperature.

The mode of operation on the original controllers (don't know about the very latest ones) is to run 10 seconds in every 30 at normal temp, then it steps up to 20 in 30 and finally 30 in 30 as the temperature rises to fixed levels above the set point.

When you turn on main beam with the standard alternator, unless you are above about 2500rpm the voltage drops and the pump switches to full time pumping. This also occurs in traffic on dipped beam when idling.
On my V8 Toledo it all worked fine with the original 80 amp Rover alternator (My Toledo has a 4 headlamp Dolomite set up). Unfortunately that died so I temporarily fitted my original MK2 Stag alternator that I removed as it was inadequate with all the efi set up and the electric pump. It was even more inadequate on the Toledo as that runs the proper EWP controller rather than a fixed resistor that draws about 4 amps rather than the 7.5 amps that the pump at full power requires.

I ended up fitting a 60 amp uprated Stag alternator to the Toledo because it was cheaper than replacing the original Rover 80 amp unit.

On the basis of this I would say leave the battery alone unless it needs replacing anyway. All my cars except the Toledo run a Toledo size battery (about the smallest available) as they are cheaper and lighter much than the Stag sized battery. My Toledo does use a Stag sized battery, but that is only because the battery is in the boot and the voltage drop down the cable necessitates a larger battery.

The after shut down running of the pump only lasts about 30 seconds and so doesn't draw much from the battery.

You may get away with the standard alternator, keep an eye on the volt meter. It won't be a problem during daylight, but may become one if you do a lot of short journeys at night.
Neil

[Stagsongas]

The only benefit for a larger battery is when you have load and the engine is not running, pump and fan running purely off the battery.

Precisely Mike, thanks.

That's exactly the part of the problem my post was written to address. Aside from things like an active alarm system, an EEWP and Electric Fan are amongst modifications that take power from the Battery when the Alternator is not charging, resulting in a discharge, perhaps to the point where the Starter won't operate. There is no doubt that a Battery with larger capacity will cope with that discharge for longer than a smaller one could.

Regards

Steve

[Stagsongas]

Steve does raise a very valid point. Roger

Nice piece Roger, but I'm afraid no point is valid on this forum unless it's made by the same old core group of closed minds and hidden agendas.